Merge remote-tracking branch 'remotes/origin/vb_undo_redo'

60 files changed, 2799 insertions, 578 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ba264c8c3..9d6d754e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -344,6 +344,10 @@ if (NOT GLEW_FOUND)
 endif ()
 include_directories(${GLEW_INCLUDE_DIRS})
 
+# Find the Cereal serialization library
+add_library(cereal INTERFACE)
+target_include_directories(cereal INTERFACE include)
+
 # l10n
 set(L10N_DIR "${SLIC3R_RESOURCES_DIR}/localization")
 add_custom_target(pot
diff --git a/deps/CMakeLists.txt b/deps/CMakeLists.txt
index 8b41c853d..f6a80f3ca 100644
--- a/deps/CMakeLists.txt
+++ b/deps/CMakeLists.txt
@@ -89,6 +89,7 @@ if (MSVC)
         dep_libcurl
         dep_wxwidgets
         dep_gtest
+        dep_cereal
         dep_nlopt
         # dep_qhull # Experimental
         dep_zlib    # on Windows we still need zlib
@@ -103,6 +104,7 @@ else()
         dep_libcurl
         dep_wxwidgets
         dep_gtest
+        dep_cereal
         dep_nlopt
         dep_qhull
         # dep_libigl # Not working, static build has different Eigen
diff --git a/deps/deps-unix-common.cmake b/deps/deps-unix-common.cmake
index 3614e9444..e323460a6 100644
--- a/deps/deps-unix-common.cmake
+++ b/deps/deps-unix-common.cmake
@@ -19,6 +19,16 @@ ExternalProject_Add(dep_gtest
     CMAKE_ARGS -DBUILD_GMOCK=OFF ${DEP_CMAKE_OPTS} -DCMAKE_INSTALL_PREFIX=${DESTDIR}/usr/local
 )
 
+ExternalProject_Add(dep_cereal
+    EXCLUDE_FROM_ALL 1
+    URL "https://github.com/USCiLab/cereal/archive/v1.2.2.tar.gz"
+#    URL_HASH SHA256=c6dd7a5701fff8ad5ebb45a3dc8e757e61d52658de3918e38bab233e7fd3b4ae
+    CMAKE_ARGS
+        -DJUST_INSTALL_CEREAL=on
+        -DCMAKE_INSTALL_PREFIX=${DESTDIR}/usr/local
+        ${DEP_CMAKE_OPTS}
+)
+
 ExternalProject_Add(dep_nlopt
     EXCLUDE_FROM_ALL 1
     URL "https://github.com/stevengj/nlopt/archive/v2.5.0.tar.gz"
diff --git a/deps/deps-windows.cmake b/deps/deps-windows.cmake
index 0b3fcb13c..9092f330b 100644
--- a/deps/deps-windows.cmake
+++ b/deps/deps-windows.cmake
@@ -115,6 +115,20 @@ if (${DEP_DEBUG})
 endif ()
 
 
+ExternalProject_Add(dep_cereal
+    EXCLUDE_FROM_ALL 1
+    URL "https://github.com/USCiLab/cereal/archive/v1.2.2.tar.gz"
+#    URL_HASH SHA256=c6dd7a5701fff8ad5ebb45a3dc8e757e61d52658de3918e38bab233e7fd3b4ae
+    CMAKE_GENERATOR "${DEP_MSVC_GEN}"
+    CMAKE_GENERATOR_PLATFORM "${DEP_PLATFORM}"
+    CMAKE_ARGS
+        -DJUST_INSTALL_CEREAL=on
+        "-DCMAKE_INSTALL_PREFIX:PATH=${DESTDIR}\\usr\\local"
+    BUILD_COMMAND msbuild /m /P:Configuration=Release INSTALL.vcxproj
+    INSTALL_COMMAND ""
+)
+
+
 ExternalProject_Add(dep_nlopt
     EXCLUDE_FROM_ALL 1
     URL "https://github.com/stevengj/nlopt/archive/v2.5.0.tar.gz"
diff --git a/doc/How to build - Mac OS.md b/doc/How to build - Mac OS.md
index 42a71e10d..b4196909d 100644
--- a/doc/How to build - Mac OS.md
+++ b/doc/How to build - Mac OS.md
@@ -20,6 +20,9 @@ You can also customize the bundle output path using the `-DDESTDIR=<some path>`
 **Warning**: Once the dependency bundle is installed in a destdir, the destdir cannot be moved elsewhere.
 (This is because wxWidgets hardcodes the installation path.)
 
+FIXME The Cereal serialization library needs a tiny patch on some old OSX clang installations
+https://github.com/USCiLab/cereal/issues/339#issuecomment-246166717
+
 
 ### Building PrusaSlicer
 
diff --git a/resources/icons/redo.svg b/resources/icons/redo.svg
new file mode 100644
index 000000000..9109779bb
--- /dev/null
+++ b/resources/icons/redo.svg
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 23.0.4, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<svg version="1.0" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" enable-background="new 0 0 16 16" xml:space="preserve">
+<g id="redo">
+	<path fill="none" stroke="#ED6B21" stroke-width="2" stroke-linecap="round" stroke-miterlimit="10" d="M13.39,11
+		c-0.91,1.78-2.76,3-4.89,3C5.46,14,3,11.54,3,8.5C3,5.46,5.46,3,8.5,3C8.67,3,8.84,3.01,9,3.03"/>
+	
+		<polygon fill="#ED6B21" stroke="#ED6B21" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" stroke-miterlimit="10" points="
+		9,1 9,5 12,3 	"/>
+</g>
+</svg>
diff --git a/resources/icons/redo_toolbar.svg b/resources/icons/redo_toolbar.svg
new file mode 100644
index 000000000..ad073244f
--- /dev/null
+++ b/resources/icons/redo_toolbar.svg
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 23.0.4, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<svg version="1.0" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" enable-background="new 0 0 16 16" xml:space="preserve">
+<g id="redo">
+	<path fill="none" stroke="#ED6B21" stroke-width="1" stroke-linecap="round" stroke-miterlimit="10" d="M13.39,11
+		c-0.91,1.78-2.76,3-4.89,3C5.46,14,3,11.54,3,8.5C3,5.46,5.46,3,8.5,3C8.67,3,8.84,3.01,9,3.03"/>
+	
+		<polygon fill="#ED6B21" stroke="#ED6B21" stroke-width="1" stroke-linecap="round" stroke-linejoin="round" stroke-miterlimit="10" points="
+		9,1 9,5 12,3 	"/>
+</g>
+</svg>
diff --git a/resources/icons/undo_toolbar.svg b/resources/icons/undo_toolbar.svg
new file mode 100644
index 000000000..699ccd807
--- /dev/null
+++ b/resources/icons/undo_toolbar.svg
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 23.0.3, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<svg version="1.0" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" enable-background="new 0 0 16 16" xml:space="preserve">
+<g id="undo">
+	<path fill="none" stroke="#ED6B21" stroke-width="1" stroke-linecap="round" stroke-miterlimit="10" d="M3,11
+		c0.91,1.78,2.76,3,4.89,3c3.04,0,5.5-2.46,5.5-5.5c0-3.04-2.46-5.5-5.5-5.5c-0.17,0-0.34,0.01-0.5,0.03"/>
+	
+		<polygon fill="#ED6B21" stroke="#ED6B21" stroke-width="1" stroke-linecap="round" stroke-linejoin="round" stroke-miterlimit="10" points="
+		7.39,1 7.39,5 4.39,3 	"/>
+</g>
+</svg>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 61faa0571..3ee46289a 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -75,7 +75,7 @@ if (NOT MSVC)
     set_target_properties(PrusaSlicer PROPERTIES OUTPUT_NAME "prusa-slicer")
 endif ()
 
-target_link_libraries(PrusaSlicer libslic3r)
+target_link_libraries(PrusaSlicer libslic3r cereal)
 if (APPLE)
 #    add_compile_options(-stdlib=libc++)
 #    add_definitions(-DBOOST_THREAD_DONT_USE_CHRONO -DBOOST_NO_CXX11_RVALUE_REFERENCES -DBOOST_THREAD_USES_MOVE)
diff --git a/src/admesh/connect.cpp b/src/admesh/connect.cpp
index e729c8922..b86ec5055 100644
--- a/src/admesh/connect.cpp
+++ b/src/admesh/connect.cpp
@@ -132,7 +132,7 @@ struct HashTableEdges {
 	~HashTableEdges() {
 #ifndef NDEBUG
 		for (int i = 0; i < this->M; ++ i)
-	    	for (HashEdge *temp = this->heads[i]; this->heads[i] != this->tail; temp = this->heads[i])
+	    	for (HashEdge *temp = this->heads[i]; temp != this->tail; temp = temp->next)
 	        	++ this->freed;
 		this->tail = nullptr;
 #endif /* NDEBUG */
diff --git a/src/libslic3r/BoundingBox.hpp b/src/libslic3r/BoundingBox.hpp
index 26302f702..b1ebdcfbc 100644
--- a/src/libslic3r/BoundingBox.hpp
+++ b/src/libslic3r/BoundingBox.hpp
@@ -161,4 +161,12 @@ inline bool empty(const BoundingBox3Base<VT> &bb)
 
 } // namespace Slic3r
 
+// Serialization through the Cereal library
+namespace cereal {
+	template<class Archive> void serialize(Archive& archive, Slic3r::BoundingBox   &bb) { archive(bb.min, bb.max, bb.defined); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::BoundingBox3  &bb) { archive(bb.min, bb.max, bb.defined); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::BoundingBoxf  &bb) { archive(bb.min, bb.max, bb.defined); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::BoundingBoxf3 &bb) { archive(bb.min, bb.max, bb.defined); }
+}
+
 #endif
diff --git a/src/libslic3r/CMakeLists.txt b/src/libslic3r/CMakeLists.txt
index ec4d85ddb..deb0ca43b 100644
--- a/src/libslic3r/CMakeLists.txt
+++ b/src/libslic3r/CMakeLists.txt
@@ -113,6 +113,8 @@ add_library(libslic3r STATIC
     MultiPoint.cpp
     MultiPoint.hpp
     MutablePriorityQueue.hpp
+    ObjectID.cpp
+    ObjectID.hpp
     PerimeterGenerator.cpp
     PerimeterGenerator.hpp
     PlaceholderParser.cpp
@@ -188,6 +190,7 @@ target_include_directories(libslic3r PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${LIBNE
 target_link_libraries(libslic3r
     libnest2d
     admesh
+    cereal
     libigl
     miniz
     boost_libs
diff --git a/src/libslic3r/Config.cpp b/src/libslic3r/Config.cpp
index 76329ccee..9d0649a1f 100644
--- a/src/libslic3r/Config.cpp
+++ b/src/libslic3r/Config.cpp
@@ -209,6 +209,51 @@ std::vector<std::string> ConfigOptionDef::cli_args(const std::string &key) const
     return args;
 }
 
+ConfigOption* ConfigOptionDef::create_empty_option() const
+{
+    switch (this->type) {
+    case coFloat:           return new ConfigOptionFloat();
+    case coFloats:          return new ConfigOptionFloats();
+    case coInt:             return new ConfigOptionInt();
+    case coInts:            return new ConfigOptionInts();
+    case coString:          return new ConfigOptionString();
+    case coStrings:         return new ConfigOptionStrings();
+    case coPercent:         return new ConfigOptionPercent();
+    case coPercents:        return new ConfigOptionPercents();
+    case coFloatOrPercent:  return new ConfigOptionFloatOrPercent();
+    case coPoint:           return new ConfigOptionPoint();
+    case coPoints:          return new ConfigOptionPoints();
+    case coPoint3:          return new ConfigOptionPoint3();
+//    case coPoint3s:         return new ConfigOptionPoint3s();
+    case coBool:            return new ConfigOptionBool();
+    case coBools:           return new ConfigOptionBools();
+    case coEnum:            return new ConfigOptionEnumGeneric(this->enum_keys_map);
+    default:                throw std::runtime_error(std::string("Unknown option type for option ") + this->label);
+    }
+}
+
+ConfigOption* ConfigOptionDef::create_default_option() const
+{
+    if (this->default_value)
+        return (this->default_value->type() == coEnum) ?
+            // Special case: For a DynamicConfig, convert a templated enum to a generic enum.
+            new ConfigOptionEnumGeneric(this->enum_keys_map, this->default_value->getInt()) :
+            this->default_value->clone();
+	return this->create_empty_option();
+}
+
+// Assignment of the serialization IDs is not thread safe. The Defs shall be initialized from the main thread!
+ConfigOptionDef* ConfigDef::add(const t_config_option_key &opt_key, ConfigOptionType type)
+{
+	static size_t serialization_key_ordinal_last = 0;
+    ConfigOptionDef *opt = &this->options[opt_key];
+    opt->opt_key = opt_key;
+    opt->type = type;
+    opt->serialization_key_ordinal = ++ serialization_key_ordinal_last;
+    this->by_serialization_key_ordinal[opt->serialization_key_ordinal] = opt;
+    return opt;
+}
+
 std::string ConfigOptionDef::nocli = "~~~noCLI";
 
 std::ostream& ConfigDef::print_cli_help(std::ostream& out, bool show_defaults, std::function<bool(const ConfigOptionDef &)> filter) const
@@ -358,7 +403,7 @@ t_config_option_keys ConfigBase::equal(const ConfigBase &other) const
     return equal;
 }
 
-std::string ConfigBase::serialize(const t_config_option_key &opt_key) const
+std::string ConfigBase::opt_serialize(const t_config_option_key &opt_key) const
 {
     const ConfigOption* opt = this->option(opt_key);
     assert(opt != nullptr);
@@ -469,7 +514,7 @@ void ConfigBase::setenv_() const
         for (size_t i = 0; i < envname.size(); ++i)
             envname[i] = (envname[i] <= 'z' && envname[i] >= 'a') ? envname[i]-('a'-'A') : envname[i];
         
-        boost::nowide::setenv(envname.c_str(), this->serialize(*it).c_str(), 1);
+        boost::nowide::setenv(envname.c_str(), this->opt_serialize(*it).c_str(), 1);
     }
 }
 
@@ -593,16 +638,16 @@ void ConfigBase::save(const std::string &file) const
     c.open(file, std::ios::out | std::ios::trunc);
     c << "# " << Slic3r::header_slic3r_generated() << std::endl;
     for (const std::string &opt_key : this->keys())
-        c << opt_key << " = " << this->serialize(opt_key) << std::endl;
+        c << opt_key << " = " << this->opt_serialize(opt_key) << std::endl;
     c.close();
 }
 
 bool DynamicConfig::operator==(const DynamicConfig &rhs) const
 {
-    t_options_map::const_iterator it1     = this->options.begin();
-    t_options_map::const_iterator it1_end = this->options.end();
-    t_options_map::const_iterator it2     = rhs.options.begin();
-    t_options_map::const_iterator it2_end = rhs.options.end();
+    auto it1     = this->options.begin();
+    auto it1_end = this->options.end();
+    auto it2     = rhs.options.begin();
+    auto it2_end = rhs.options.end();
     for (; it1 != it1_end && it2 != it2_end; ++ it1, ++ it2)
 		if (it1->first != it2->first || *it1->second != *it2->second)
 			// key or value differ
@@ -612,10 +657,10 @@ bool DynamicConfig::operator==(const DynamicConfig &rhs) const
 
 ConfigOption* DynamicConfig::optptr(const t_config_option_key &opt_key, bool create)
 {
-    t_options_map::iterator it = options.find(opt_key);
+    auto it = options.find(opt_key);
     if (it != options.end())
         // Option was found.
-        return it->second;
+        return it->second.get();
     if (! create)
         // Option was not found and a new option shall not be created.
         return nullptr;
@@ -628,34 +673,8 @@ ConfigOption* DynamicConfig::optptr(const t_config_option_key &opt_key, bool cre
 //        throw std::runtime_error(std::string("Invalid option name: ") + opt_key);
         // Let the parent decide what to do if the opt_key is not defined by this->def().
         return nullptr;
-    ConfigOption *opt = nullptr;
-    if (optdef->default_value) {
-        opt = (optdef->default_value->type() == coEnum) ?
-            // Special case: For a DynamicConfig, convert a templated enum to a generic enum.
-            new ConfigOptionEnumGeneric(optdef->enum_keys_map, optdef->default_value->getInt()) :
-            optdef->default_value->clone();
-    } else {
-        switch (optdef->type) {
-        case coFloat:           opt = new ConfigOptionFloat();          break;
-        case coFloats:          opt = new ConfigOptionFloats();         break;
-        case coInt:             opt = new ConfigOptionInt();            break;
-        case coInts:            opt = new ConfigOptionInts();           break;
-        case coString:          opt = new ConfigOptionString();         break;
-        case coStrings:         opt = new ConfigOptionStrings();        break;
-        case coPercent:         opt = new ConfigOptionPercent();        break;
-        case coPercents:        opt = new ConfigOptionPercents();       break;
-        case coFloatOrPercent:  opt = new ConfigOptionFloatOrPercent(); break;
-        case coPoint:           opt = new ConfigOptionPoint();          break;
-        case coPoints:          opt = new ConfigOptionPoints();         break;
-        case coPoint3:          opt = new ConfigOptionPoint3();         break;
-    //    case coPoint3s:         opt = new ConfigOptionPoint3s();        break;
-        case coBool:            opt = new ConfigOptionBool();           break;
-        case coBools:           opt = new ConfigOptionBools();          break;
-        case coEnum:            opt = new ConfigOptionEnumGeneric(optdef->enum_keys_map); break;
-        default:                throw std::runtime_error(std::string("Unknown option type for option ") + opt_key);
-        }
-    }
-    this->options[opt_key] = opt;
+    ConfigOption *opt = optdef->create_default_option();
+    this->options.emplace_hint(it, opt_key, std::unique_ptr<ConfigOption>(opt));
     return opt;
 }
 
@@ -802,3 +821,64 @@ t_config_option_keys StaticConfig::keys() const
 }
 
 }
+
+#include <cereal/types/polymorphic.hpp>
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOption)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<double>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<int>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<std::string>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<Slic3r::Vec2d>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<Slic3r::Vec3d>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionSingle<bool>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVectorBase)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVector<double>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVector<int>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVector<std::string>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVector<Slic3r::Vec2d>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionVector<unsigned char>)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionFloat)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionFloats)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionInt)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionInts)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionString)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionStrings)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionPercent)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionPercents)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionFloatOrPercent)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionPoint)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionPoints)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionPoint3)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionBool)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionBools)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigOptionEnumGeneric)
+CEREAL_REGISTER_TYPE(Slic3r::ConfigBase)
+CEREAL_REGISTER_TYPE(Slic3r::DynamicConfig)
+
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<double>) 
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<int>) 
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<std::string>) 
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<Slic3r::Vec2d>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<Slic3r::Vec3d>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionSingle<bool>) 
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOption, Slic3r::ConfigOptionVectorBase) 
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVectorBase, Slic3r::ConfigOptionVector<double>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVectorBase, Slic3r::ConfigOptionVector<int>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVectorBase, Slic3r::ConfigOptionVector<std::string>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVectorBase, Slic3r::ConfigOptionVector<Slic3r::Vec2d>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVectorBase, Slic3r::ConfigOptionVector<unsigned char>)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<double>, Slic3r::ConfigOptionFloat)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVector<double>, Slic3r::ConfigOptionFloats)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<int>, Slic3r::ConfigOptionInt)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVector<int>, Slic3r::ConfigOptionInts)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<std::string>, Slic3r::ConfigOptionString)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVector<std::string>, Slic3r::ConfigOptionStrings)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionFloat, Slic3r::ConfigOptionPercent)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionFloats, Slic3r::ConfigOptionPercents)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionPercent, Slic3r::ConfigOptionFloatOrPercent)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<Slic3r::Vec2d>, Slic3r::ConfigOptionPoint)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVector<Slic3r::Vec2d>, Slic3r::ConfigOptionPoints)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<Slic3r::Vec3d>, Slic3r::ConfigOptionPoint3)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionSingle<bool>, Slic3r::ConfigOptionBool)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionVector<unsigned char>, Slic3r::ConfigOptionBools)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigOptionInt, Slic3r::ConfigOptionEnumGeneric)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ConfigBase, Slic3r::DynamicConfig)
diff --git a/src/libslic3r/Config.hpp b/src/libslic3r/Config.hpp
index a7192a558..844287efb 100644
--- a/src/libslic3r/Config.hpp
+++ b/src/libslic3r/Config.hpp
@@ -18,6 +18,9 @@
 #include <boost/format.hpp>
 #include <boost/property_tree/ptree.hpp>
 
+#include <cereal/access.hpp>
+#include <cereal/types/base_class.hpp>
+
 namespace Slic3r {
 
 // Name of the configuration option.
@@ -152,6 +155,10 @@ public:
 
     bool operator==(const T &rhs) const { return this->value == rhs; }
     bool operator!=(const T &rhs) const { return this->value != rhs; }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive & ar) { ar(this->value); }
 };
 
 // Value of a vector valued option (bools, ints, floats, strings, points)
@@ -294,6 +301,10 @@ public:
 
     bool operator==(const std::vector<T> &rhs) const { return this->values == rhs; }
     bool operator!=(const std::vector<T> &rhs) const { return this->values != rhs; }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive & ar) { ar(this->values); }
 };
 
 class ConfigOptionFloat : public ConfigOptionSingle<double>
@@ -328,6 +339,10 @@ public:
         this->set(opt);
         return *this;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<double>>(this)); }
 };
 
 class ConfigOptionFloats : public ConfigOptionVector<double>
@@ -386,6 +401,10 @@ public:
         this->set(opt);
         return *this;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionVector<double>>(this)); }
 };
 
 class ConfigOptionInt : public ConfigOptionSingle<int>
@@ -422,6 +441,10 @@ public:
         this->set(opt);
         return *this;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<int>>(this)); }
 };
 
 class ConfigOptionInts : public ConfigOptionVector<int>
@@ -472,6 +495,10 @@ public:
         }
         return true;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionVector<int>>(this)); }
 };
 
 class ConfigOptionString : public ConfigOptionSingle<std::string>
@@ -496,6 +523,10 @@ public:
         UNUSED(append);
         return unescape_string_cstyle(str, this->value);
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<std::string>>(this)); }
 };
 
 // semicolon-separated strings
@@ -530,6 +561,10 @@ public:
             this->values.clear();
         return unescape_strings_cstyle(str, this->values);
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionVector<std::string>>(this)); }
 };
 
 class ConfigOptionPercent : public ConfigOptionFloat
@@ -562,6 +597,10 @@ public:
         iss >> this->value;
         return !iss.fail();
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionFloat>(this)); }
 };
 
 class ConfigOptionPercents : public ConfigOptionFloats
@@ -616,6 +655,10 @@ public:
         }
         return true;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionFloats>(this)); }
 };
 
 class ConfigOptionFloatOrPercent : public ConfigOptionPercent
@@ -665,6 +708,10 @@ public:
         iss >> this->value;
         return !iss.fail();
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionPercent>(this), percent); }
 };
 
 class ConfigOptionPoint : public ConfigOptionSingle<Vec2d>
@@ -695,6 +742,10 @@ public:
         return sscanf(str.data(), " %lf , %lf %c", &this->value(0), &this->value(1), &dummy) == 2 ||
                sscanf(str.data(), " %lf x %lf %c", &this->value(0), &this->value(1), &dummy) == 2;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<Vec2d>>(this)); }
 };
 
 class ConfigOptionPoints : public ConfigOptionVector<Vec2d>
@@ -754,8 +805,21 @@ public:
         }
         return true;
     }
-};
 
+private:
+	friend class cereal::access;
+	template<class Archive> void save(Archive& archive) const {
+		size_t cnt = this->values.size();
+		archive(cnt);
+		archive.saveBinary((const char*)this->values.data(), sizeof(Vec2d) * cnt);
+	}
+	template<class Archive> void load(Archive& archive) {
+		size_t cnt;
+		archive(cnt);
+		this->values.assign(cnt, Vec2d());
+		archive.loadBinary((char*)this->values.data(), sizeof(Vec2d) * cnt);
+	}
+};
 
 class ConfigOptionPoint3 : public ConfigOptionSingle<Vec3d>
 {
@@ -787,6 +851,10 @@ public:
         return sscanf(str.data(), " %lf , %lf , %lf %c", &this->value(0), &this->value(1), &this->value(2), &dummy) == 2 ||
                sscanf(str.data(), " %lf x %lf x %lf %c", &this->value(0), &this->value(1), &this->value(2), &dummy) == 2;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<Vec3d>>(this)); }
 };
 
 class ConfigOptionBool : public ConfigOptionSingle<bool>
@@ -813,6 +881,10 @@ public:
         this->value = (str.compare("1") == 0);
         return true;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionSingle<bool>>(this)); }
 };
 
 class ConfigOptionBools : public ConfigOptionVector<unsigned char>
@@ -868,6 +940,10 @@ public:
         }
         return true;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(cereal::base_class<ConfigOptionVector<unsigned char>>(this)); }
 };
 
 // Map from an enum integer value to an enum name.
@@ -1006,19 +1082,73 @@ public:
         this->value = it->second;
         return true;
     }
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive& ar) { ar(cereal::base_class<ConfigOptionInt>(this)); }
 };
 
 // Definition of a configuration value for the purpose of GUI presentation, editing, value mapping and config file handling.
 class ConfigOptionDef
 {
 public:
+	// Identifier of this option. It is stored here so that it is accessible through the by_serialization_key_ordinal map.
+	t_config_option_key 				opt_key;
     // What type? bool, int, string etc.
     ConfigOptionType                    type            = coNone;
     // Default value of this option. The default value object is owned by ConfigDef, it is released in its destructor.
     Slic3r::clonable_ptr<const ConfigOption> default_value;
-    void set_default_value(const ConfigOption* ptr) { this->default_value = Slic3r::clonable_ptr<const ConfigOption>(ptr); }
-    template<typename T>
-    const T* get_default_value() const { return static_cast<const T*>(this->default_value.get()); }
+    void 								set_default_value(const ConfigOption* ptr) { this->default_value = Slic3r::clonable_ptr<const ConfigOption>(ptr); }
+    template<typename T> const T* 		get_default_value() const { return static_cast<const T*>(this->default_value.get()); }
+
+    // Create an empty option to be used as a base for deserialization of DynamicConfig.
+    ConfigOption*						create_empty_option() const;
+    // Create a default option to be inserted into a DynamicConfig.
+    ConfigOption*						create_default_option() const;
+
+    template<class Archive> ConfigOption* load_option_from_archive(Archive &archive) const {
+	    switch (this->type) {
+	    case coFloat:           { auto opt = new ConfigOptionFloat();  			archive(*opt); return opt; }
+	    case coFloats:          { auto opt = new ConfigOptionFloats(); 			archive(*opt); return opt; }
+	    case coInt:             { auto opt = new ConfigOptionInt();    			archive(*opt); return opt; }
+	    case coInts:            { auto opt = new ConfigOptionInts();   			archive(*opt); return opt; }
+	    case coString:          { auto opt = new ConfigOptionString(); 			archive(*opt); return opt; }
+	    case coStrings:         { auto opt = new ConfigOptionStrings(); 		archive(*opt); return opt; }
+	    case coPercent:         { auto opt = new ConfigOptionPercent(); 		archive(*opt); return opt; }
+	    case coPercents:        { auto opt = new ConfigOptionPercents(); 		archive(*opt); return opt; }
+	    case coFloatOrPercent:  { auto opt = new ConfigOptionFloatOrPercent(); 	archive(*opt); return opt; }
+	    case coPoint:           { auto opt = new ConfigOptionPoint(); 			archive(*opt); return opt; }
+	    case coPoints:          { auto opt = new ConfigOptionPoints(); 			archive(*opt); return opt; }
+	    case coPoint3:          { auto opt = new ConfigOptionPoint3(); 			archive(*opt); return opt; }
+	    case coBool:            { auto opt = new ConfigOptionBool(); 			archive(*opt); return opt; }
+	    case coBools:           { auto opt = new ConfigOptionBools(); 			archive(*opt); return opt; }
+	    case coEnum:            { auto opt = new ConfigOptionEnumGeneric(this->enum_keys_map); archive(*opt); return opt; }
+	    default:                throw std::runtime_error(std::string("ConfigOptionDef::load_option_from_archive(): Unknown option type for option ") + this->opt_key);
+	    }
+	}
+
+    template<class Archive> ConfigOption* save_option_to_archive(Archive &archive, const ConfigOption *opt) const {
+	    switch (this->type) {
+	    case coFloat:           archive(*static_cast<const ConfigOptionFloat*>(opt));  			break;
+	    case coFloats:          archive(*static_cast<const ConfigOptionFloats*>(opt)); 			break;
+	    case coInt:             archive(*static_cast<const ConfigOptionInt*>(opt)); 	 		break;
+	    case coInts:            archive(*static_cast<const ConfigOptionInts*>(opt)); 	 		break;
+	    case coString:          archive(*static_cast<const ConfigOptionString*>(opt)); 			break;
+	    case coStrings:         archive(*static_cast<const ConfigOptionStrings*>(opt)); 		break;
+	    case coPercent:         archive(*static_cast<const ConfigOptionPercent*>(opt)); 		break;
+	    case coPercents:        archive(*static_cast<const ConfigOptionPercents*>(opt)); 		break;
+	    case coFloatOrPercent:  archive(*static_cast<const ConfigOptionFloatOrPercent*>(opt));	break;
+	    case coPoint:           archive(*static_cast<const ConfigOptionPoint*>(opt)); 			break;
+	    case coPoints:          archive(*static_cast<const ConfigOptionPoints*>(opt)); 			break;
+	    case coPoint3:          archive(*static_cast<const ConfigOptionPoint3*>(opt)); 			break;
+	    case coBool:            archive(*static_cast<const ConfigOptionBool*>(opt)); 			break;
+	    case coBools:           archive(*static_cast<const ConfigOptionBools*>(opt)); 			break;
+	    case coEnum:            archive(*static_cast<const ConfigOptionEnumGeneric*>(opt)); 	break;
+	    default:                throw std::runtime_error(std::string("ConfigOptionDef::save_option_to_archive(): Unknown option type for option ") + this->opt_key);
+	    }
+		// Make the compiler happy, shut up the warnings.
+		return nullptr;
+	}
 
     // Usually empty. 
     // Special values - "i_enum_open", "f_enum_open" to provide combo box for int or float selection,
@@ -1088,6 +1218,9 @@ public:
         return false;
     }
 
+    // 0 is an invalid key.
+    size_t 								serialization_key_ordinal = 0;
+
     // Returns the alternative CLI arguments for the given option.
     // If there are no cli arguments defined, use the key and replace underscores with dashes.
     std::vector<std::string> cli_args(const std::string &key) const;
@@ -1107,7 +1240,8 @@ typedef std::map<t_config_option_key, ConfigOptionDef> t_optiondef_map;
 class ConfigDef
 {
 public:
-    t_optiondef_map         options;
+    t_optiondef_map         					options;
+    std::map<size_t, const ConfigOptionDef*>	by_serialization_key_ordinal;
 
     bool                    has(const t_config_option_key &opt_key) const { return this->options.count(opt_key) > 0; }
     const ConfigOptionDef*  get(const t_config_option_key &opt_key) const {
@@ -1128,11 +1262,7 @@ public:
         std::function<bool(const ConfigOptionDef &)> filter = [](const ConfigOptionDef &){ return true; }) const;
 
 protected:
-    ConfigOptionDef*        add(const t_config_option_key &opt_key, ConfigOptionType type) {
-        ConfigOptionDef* opt = &this->options[opt_key];
-        opt->type = type;
-        return opt;
-    }
+    ConfigOptionDef*        add(const t_config_option_key &opt_key, ConfigOptionType type);
 };
 
 // An abstract configuration store.
@@ -1201,7 +1331,7 @@ public:
     bool equals(const ConfigBase &other) const { return this->diff(other).empty(); }
     t_config_option_keys diff(const ConfigBase &other) const;
     t_config_option_keys equal(const ConfigBase &other) const;
-    std::string serialize(const t_config_option_key &opt_key) const;
+    std::string opt_serialize(const t_config_option_key &opt_key) const;
     // Set a configuration value from a string, it will call an overridable handle_legacy() 
     // to resolve renamed and removed configuration keys.
     bool set_deserialize(const t_config_option_key &opt_key, const std::string &str, bool append = false);
@@ -1239,7 +1369,7 @@ public:
         assert(this->def() == nullptr || this->def() == rhs.def());
         this->clear();
         for (const auto &kvp : rhs.options)
-            this->options[kvp.first] = kvp.second->clone();
+            this->options[kvp.first].reset(kvp.second->clone());
         return *this;
     }
 
@@ -1262,15 +1392,13 @@ public:
         for (const auto &kvp : rhs.options) {
             auto it = this->options.find(kvp.first);
             if (it == this->options.end())
-                this->options[kvp.first] = kvp.second->clone();
+                this->options[kvp.first].reset(kvp.second->clone());
             else {
                 assert(it->second->type() == kvp.second->type());
                 if (it->second->type() == kvp.second->type())
                     *it->second = *kvp.second;
-                else {
-                    delete it->second;
-                    it->second = kvp.second->clone();
-                }
+                else
+                    it->second.reset(kvp.second->clone());
             }
         }
         return *this;
@@ -1281,14 +1409,13 @@ public:
     DynamicConfig& operator+=(DynamicConfig &&rhs) 
     {
         assert(this->def() == nullptr || this->def() == rhs.def());
-        for (const auto &kvp : rhs.options) {
+        for (auto &kvp : rhs.options) {
             auto it = this->options.find(kvp.first);
             if (it == this->options.end()) {
-                this->options[kvp.first] = kvp.second;
+                this->options.insert(std::make_pair(kvp.first, std::move(kvp.second)));
             } else {
                 assert(it->second->type() == kvp.second->type());
-                delete it->second;
-                it->second = kvp.second;
+                it->second = std::move(kvp.second);
             }
         }
         rhs.options.clear();
@@ -1305,8 +1432,6 @@ public:
 
     void clear()
     { 
-        for (auto &opt : this->options) 
-            delete opt.second; 
         this->options.clear(); 
     }
 
@@ -1315,7 +1440,6 @@ public:
         auto it = this->options.find(opt_key);
         if (it == this->options.end())
             return false;
-        delete it->second;
         this->options.erase(it);
         return true;
     }
@@ -1340,11 +1464,10 @@ public:
     {
         auto it = this->options.find(opt_key);
         if (it == this->options.end()) {
-            this->options[opt_key] = opt;
+            this->options[opt_key].reset(opt);
             return true;
         } else {
-            delete it->second;
-            it->second = opt;
+            it->second.reset(opt);
             return false;
         }
     }
@@ -1374,12 +1497,15 @@ public:
     void                read_cli(const std::vector<std::string> &tokens, t_config_option_keys* extra, t_config_option_keys* keys = nullptr);
     bool                read_cli(int argc, char** argv, t_config_option_keys* extra, t_config_option_keys* keys = nullptr);
 
-    typedef std::map<t_config_option_key,ConfigOption*> t_options_map;
-    t_options_map::const_iterator cbegin() const { return options.cbegin(); }
-    t_options_map::const_iterator cend()   const { return options.cend(); }
+    std::map<t_config_option_key, std::unique_ptr<ConfigOption>>::const_iterator cbegin() const { return options.cbegin(); }
+    std::map<t_config_option_key, std::unique_ptr<ConfigOption>>::const_iterator cend()   const { return options.cend(); }
+    size_t                        												 size()   const { return options.size(); }
 
 private:
-    t_options_map options;
+    std::map<t_config_option_key, std::unique_ptr<ConfigOption>> options;
+
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(options); }
 };
 
 /// Configuration store with a static definition of configuration values.
diff --git a/src/libslic3r/Format/3mf.cpp b/src/libslic3r/Format/3mf.cpp
index b866e640e..21c680d2d 100644
--- a/src/libslic3r/Format/3mf.cpp
+++ b/src/libslic3r/Format/3mf.cpp
@@ -2134,7 +2134,7 @@ namespace Slic3r {
                     const DynamicPrintConfig& config = range.second;
                     for (const std::string& opt_key : config.keys())
                     {
-                        pt::ptree& opt_tree = range_tree.add("option", config.serialize(opt_key));
+                        pt::ptree& opt_tree = range_tree.add("option", config.opt_serialize(opt_key));
                         opt_tree.put("<xmlattr>.opt_key", opt_key);
                     }
                 }
@@ -2216,7 +2216,7 @@ namespace Slic3r {
 
         for (const std::string &key : config.keys())
             if (key != "compatible_printers")
-                out += "; " + key + " = " + config.serialize(key) + "\n";
+                out += "; " + key + " = " + config.opt_serialize(key) + "\n";
 
         if (!out.empty())
         {
@@ -2250,7 +2250,7 @@ namespace Slic3r {
                 // stores object's config data
                 for (const std::string& key : obj->config.keys())
                 {
-                    stream << "  <" << METADATA_TAG << " " << TYPE_ATTR << "=\"" << OBJECT_TYPE << "\" " << KEY_ATTR << "=\"" << key << "\" " << VALUE_ATTR << "=\"" << obj->config.serialize(key) << "\"/>\n";
+                    stream << "  <" << METADATA_TAG << " " << TYPE_ATTR << "=\"" << OBJECT_TYPE << "\" " << KEY_ATTR << "=\"" << key << "\" " << VALUE_ATTR << "=\"" << obj->config.opt_serialize(key) << "\"/>\n";
                 }
 
                 for (const ModelVolume* volume : obj_metadata.second.object->volumes)
@@ -2280,7 +2280,7 @@ namespace Slic3r {
                             // stores volume's config data
                             for (const std::string& key : volume->config.keys())
                             {
-                                stream << "   <" << METADATA_TAG << " " << TYPE_ATTR << "=\"" << VOLUME_TYPE << "\" " << KEY_ATTR << "=\"" << key << "\" " << VALUE_ATTR << "=\"" << volume->config.serialize(key) << "\"/>\n";
+                                stream << "   <" << METADATA_TAG << " " << TYPE_ATTR << "=\"" << VOLUME_TYPE << "\" " << KEY_ATTR << "=\"" << key << "\" " << VALUE_ATTR << "=\"" << volume->config.opt_serialize(key) << "\"/>\n";
                             }
 
                             stream << "  </" << VOLUME_TAG << ">\n";
diff --git a/src/libslic3r/Format/AMF.cpp b/src/libslic3r/Format/AMF.cpp
index 90a538731..e964d3b9d 100644
--- a/src/libslic3r/Format/AMF.cpp
+++ b/src/libslic3r/Format/AMF.cpp
@@ -901,7 +901,7 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
         std::string str_config = "\n";
         for (const std::string &key : config->keys())
             if (key != "compatible_printers")
-                str_config += "; " + key + " = " + config->serialize(key) + "\n";
+                str_config += "; " + key + " = " + config->opt_serialize(key) + "\n";
         stream << "<metadata type=\"" << SLIC3R_CONFIG_TYPE << "\">" << xml_escape(str_config) << "</metadata>\n";
     }
 
@@ -913,7 +913,7 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
         for (const auto &attr : material.second->attributes)
             stream << "    <metadata type=\"" << attr.first << "\">" << attr.second << "</metadata>\n";
         for (const std::string &key : material.second->config.keys())
-            stream << "    <metadata type=\"slic3r." << key << "\">" << material.second->config.serialize(key) << "</metadata>\n";
+            stream << "    <metadata type=\"slic3r." << key << "\">" << material.second->config.opt_serialize(key) << "</metadata>\n";
         stream << "  </material>\n";
     }
     std::string instances;
@@ -921,7 +921,7 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
         ModelObject *object = model->objects[object_id];
         stream << "  <object id=\"" << object_id << "\">\n";
         for (const std::string &key : object->config.keys())
-            stream << "    <metadata type=\"slic3r." << key << "\">" << object->config.serialize(key) << "</metadata>\n";
+            stream << "    <metadata type=\"slic3r." << key << "\">" << object->config.opt_serialize(key) << "</metadata>\n";
         if (!object->name.empty())
             stream << "    <metadata type=\"name\">" << xml_escape(object->name) << "</metadata>\n";
         const std::vector<double> &layer_height_profile = object->layer_height_profile;
@@ -933,10 +933,8 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
                 stream << ";" << layer_height_profile[i];
                 stream << "\n    </metadata>\n";
         }
-        //FIXME Store the layer height ranges (ModelObject::layer_height_ranges)
 
-
-        // #ys_FIXME_experiment : Try to export layer config range
+        // Export layer height ranges including the layer range specific config overrides.
         const t_layer_config_ranges& config_ranges = object->layer_config_ranges;
         if (!config_ranges.empty())
         {
@@ -950,7 +948,7 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
                 stream << range.first.first << ";" << range.first.second << "</metadata>\n";
 
                 for (const std::string& key : range.second.keys())
-                    stream << "        <metadata type=\"slic3r." << key << "\">" << range.second.serialize(key) << "</metadata>\n";
+                    stream << "        <metadata type=\"slic3r." << key << "\">" << range.second.opt_serialize(key) << "</metadata>\n";
 
                 stream << "      </range>\n";
                 layer_counter++;
@@ -1005,7 +1003,7 @@ bool store_amf(const char *path, Model *model, const DynamicPrintConfig *config)
             else
                 stream << "      <volume materialid=\"" << volume->material_id() << "\">\n";
             for (const std::string &key : volume->config.keys())
-                stream << "        <metadata type=\"slic3r." << key << "\">" << volume->config.serialize(key) << "</metadata>\n";
+                stream << "        <metadata type=\"slic3r." << key << "\">" << volume->config.opt_serialize(key) << "</metadata>\n";
             if (!volume->name.empty())
                 stream << "        <metadata type=\"name\">" << xml_escape(volume->name) << "</metadata>\n";
             if (volume->is_modifier())
diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index 47cc61882..42e402a24 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -1809,7 +1809,7 @@ void GCode::append_full_config(const Print& print, std::string& str)
         const StaticPrintConfig *cfg = configs[i];
         for (const std::string &key : cfg->keys())
             if (key != "compatible_printers")
-                str += "; " + key + " = " + cfg->serialize(key) + "\n";
+                str += "; " + key + " = " + cfg->opt_serialize(key) + "\n";
     }
     const DynamicConfig &full_config = print.placeholder_parser().config();
 	for (const char *key : {
diff --git a/src/libslic3r/Geometry.hpp b/src/libslic3r/Geometry.hpp
index bcbe80a0d..dca1872d8 100644
--- a/src/libslic3r/Geometry.hpp
+++ b/src/libslic3r/Geometry.hpp
@@ -7,6 +7,9 @@
 #include "Polygon.hpp"
 #include "Polyline.hpp"
 
+// Serialization through the Cereal library
+#include <cereal/access.hpp>
+
 #include "boost/polygon/voronoi.hpp"
 using boost::polygon::voronoi_builder;
 using boost::polygon::voronoi_diagram;
@@ -263,6 +266,17 @@ public:
     // as possible in least squares norm in regard to the 8 corners of bbox.
     // Bounding box is expected to be centered around zero in all axes.
     static Transformation volume_to_bed_transformation(const Transformation& instance_transformation, const BoundingBoxf3& bbox);
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive & ar) { ar(m_offset, m_rotation, m_scaling_factor, m_mirror); }
+	explicit Transformation(int) : m_dirty(true) {}
+	template <class Archive> static void load_and_construct(Archive &ar, cereal::construct<Transformation> &construct)
+	{
+		// Calling a private constructor with special "int" parameter to indicate that no construction is necessary.
+		construct(1);
+		ar(construct.ptr()->m_offset, construct.ptr()->m_rotation, construct.ptr()->m_scaling_factor, construct.ptr()->m_mirror);
+	}
 };
 
 // Rotation when going from the first coordinate system with rotation rot_xyz_from applied
diff --git a/src/libslic3r/Layer.cpp b/src/libslic3r/Layer.cpp
index c1d92c6bb..a8160867a 100644
--- a/src/libslic3r/Layer.cpp
+++ b/src/libslic3r/Layer.cpp
@@ -128,7 +128,7 @@ void Layer::make_perimeters()
                 && config.external_perimeter_speed == other_config.external_perimeter_speed
                 && config.gap_fill_speed    == other_config.gap_fill_speed
                 && config.overhangs         == other_config.overhangs
-                && config.serialize("perimeter_extrusion_width").compare(other_config.serialize("perimeter_extrusion_width")) == 0
+                && config.opt_serialize("perimeter_extrusion_width") == other_config.opt_serialize("perimeter_extrusion_width")
                 && config.thin_walls        == other_config.thin_walls
                 && config.external_perimeters_first == other_config.external_perimeters_first) {
                 layerms.push_back(other_layerm);
diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 173638c03..949f82c0a 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -22,21 +22,6 @@ namespace Slic3r {
 
 unsigned int Model::s_auto_extruder_id = 1;
 
-size_t ModelBase::s_last_id = 0;
-
-// Unique object / instance ID for the wipe tower.
-ModelID wipe_tower_object_id()
-{
-    static ModelBase mine;
-    return mine.id();
-}
-
-ModelID wipe_tower_instance_id()
-{
-    static ModelBase mine;
-    return mine.id();
-}
-
 Model& Model::assign_copy(const Model &rhs)
 {
     this->copy_id(rhs);
@@ -87,6 +72,19 @@ void Model::assign_new_unique_ids_recursive()
         model_object->assign_new_unique_ids_recursive();
 }
 
+void Model::update_links_bottom_up_recursive()
+{
+	for (std::pair<const t_model_material_id, ModelMaterial*> &kvp : this->materials)
+		kvp.second->set_model(this);
+	for (ModelObject *model_object : this->objects) {
+		model_object->set_model(this);
+		for (ModelInstance *model_instance : model_object->instances)
+			model_instance->set_model_object(model_object);
+		for (ModelVolume *model_volume : model_object->volumes)
+			model_volume->set_model_object(model_object);
+	}
+}
+
 Model Model::read_from_file(const std::string &input_file, DynamicPrintConfig *config, bool add_default_instances)
 {
     Model model;
@@ -221,7 +219,7 @@ bool Model::delete_object(ModelObject* object)
     return false;
 }
 
-bool Model::delete_object(ModelID id)
+bool Model::delete_object(ObjectID id)
 {
     if (id.id != 0) {
         size_t idx = 0;
@@ -622,11 +620,15 @@ ModelObject::~ModelObject()
 // maintains the m_model pointer
 ModelObject& ModelObject::assign_copy(const ModelObject &rhs)
 {
-    this->copy_id(rhs);
+	assert(this->id().invalid() || this->id() == rhs.id());
+	assert(this->config.id().invalid() || this->config.id() == rhs.config.id());
+	this->copy_id(rhs);
 
     this->name                        = rhs.name;
     this->input_file                  = rhs.input_file;
+    // Copies the config's ID
     this->config                      = rhs.config;
+    assert(this->config.id() == rhs.config.id());
     this->sla_support_points          = rhs.sla_support_points;
     this->sla_points_status           = rhs.sla_points_status;
     this->layer_config_ranges         = rhs.layer_config_ranges;    // #ys_FIXME_experiment
@@ -658,11 +660,14 @@ ModelObject& ModelObject::assign_copy(const ModelObject &rhs)
 // maintains the m_model pointer
 ModelObject& ModelObject::assign_copy(ModelObject &&rhs)
 {
+	assert(this->id().invalid());
     this->copy_id(rhs);
 
     this->name                        = std::move(rhs.name);
     this->input_file                  = std::move(rhs.input_file);
+    // Moves the config's ID
     this->config                      = std::move(rhs.config);
+    assert(this->config.id() == rhs.config.id());
     this->sla_support_points          = std::move(rhs.sla_support_points);
     this->sla_points_status           = std::move(rhs.sla_points_status);
     this->layer_config_ranges         = std::move(rhs.layer_config_ranges); // #ys_FIXME_experiment
@@ -1070,11 +1075,11 @@ void ModelObject::mirror(Axis axis)
 }
 
 // This method could only be called before the meshes of this ModelVolumes are not shared!
-void ModelObject::scale_mesh(const Vec3d &versor)
+void ModelObject::scale_mesh_after_creation(const Vec3d &versor)
 {
     for (ModelVolume *v : this->volumes)
     {
-        v->scale_geometry(versor);
+        v->scale_geometry_after_creation(versor);
         v->set_offset(versor.cwiseProduct(v->get_offset()));
     }
     this->invalidate_bounding_box();
@@ -1191,13 +1196,19 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, bool keep_upper, b
             if (keep_upper && upper_mesh.facets_count() > 0) {
                 ModelVolume* vol = upper->add_volume(upper_mesh);
                 vol->name	= volume->name;
-                vol->config = volume->config;
+                // Don't copy the config's ID.
+				static_cast<DynamicPrintConfig&>(vol->config) = static_cast<const DynamicPrintConfig&>(volume->config);
+    			assert(vol->config.id().valid());
+	    		assert(vol->config.id() != volume->config.id());
                 vol->set_material(volume->material_id(), *volume->material());
             }
             if (keep_lower && lower_mesh.facets_count() > 0) {
                 ModelVolume* vol = lower->add_volume(lower_mesh);
                 vol->name	= volume->name;
-                vol->config = volume->config;
+                // Don't copy the config's ID.
+				static_cast<DynamicPrintConfig&>(vol->config) = static_cast<const DynamicPrintConfig&>(volume->config);
+    			assert(vol->config.id().valid());
+	    		assert(vol->config.id() != volume->config.id());
                 vol->set_material(volume->material_id(), *volume->material());
 
                 // Compute the lower part instances' bounding boxes to figure out where to place
@@ -1272,7 +1283,10 @@ void ModelObject::split(ModelObjectPtrs* new_objects)
         // XXX: this seems to be the only real usage of m_model, maybe refactor this so that it's not needed?
         ModelObject* new_object = m_model->add_object();    
         new_object->name   = this->name;
-        new_object->config = this->config;
+        // Don't copy the config's ID.
+		static_cast<DynamicPrintConfig&>(new_object->config) = static_cast<const DynamicPrintConfig&>(this->config);
+		assert(new_object->config.id().valid());
+		assert(new_object->config.id() != this->config.id());
         new_object->instances.reserve(this->instances.size());
         for (const ModelInstance *model_instance : this->instances)
             new_object->add_instance(*model_instance);
@@ -1565,9 +1579,9 @@ void ModelVolume::center_geometry_after_creation()
     if (!shift.isApprox(Vec3d::Zero()))
     {
     	if (m_mesh)
-        	m_mesh->translate(-(float)shift(0), -(float)shift(1), -(float)shift(2));
+        	const_cast<TriangleMesh*>(m_mesh.get())->translate(-(float)shift(0), -(float)shift(1), -(float)shift(2));
         if (m_convex_hull)
-        	m_convex_hull->translate(-(float)shift(0), -(float)shift(1), -(float)shift(2));
+			const_cast<TriangleMesh*>(m_convex_hull.get())->translate(-(float)shift(0), -(float)shift(1), -(float)shift(2));
         translate(shift);
     }
 }
@@ -1720,10 +1734,10 @@ void ModelVolume::mirror(Axis axis)
 }
 
 // This method could only be called before the meshes of this ModelVolumes are not shared!
-void ModelVolume::scale_geometry(const Vec3d& versor)
+void ModelVolume::scale_geometry_after_creation(const Vec3d& versor)
 {
-    m_mesh->scale(versor);
-    m_convex_hull->scale(versor);
+	const_cast<TriangleMesh*>(m_mesh.get())->scale(versor);
+	const_cast<TriangleMesh*>(m_convex_hull.get())->scale(versor);
 }
 
 void ModelVolume::transform_this_mesh(const Transform3d &mesh_trafo, bool fix_left_handed)
@@ -1867,21 +1881,26 @@ bool model_volume_list_changed(const ModelObject &model_object_old, const ModelO
 // Verify whether the IDs of Model / ModelObject / ModelVolume / ModelInstance / ModelMaterial are valid and unique.
 void check_model_ids_validity(const Model &model)
 {
-    std::set<ModelID> ids;
-    auto check = [&ids](ModelID id) { 
-        assert(id.id > 0);
+    std::set<ObjectID> ids;
+    auto check = [&ids](ObjectID id) { 
+        assert(id.valid());
         assert(ids.find(id) == ids.end());
         ids.insert(id);
     };
     for (const ModelObject *model_object : model.objects) {
         check(model_object->id());
-        for (const ModelVolume *model_volume : model_object->volumes)
+        check(model_object->config.id());
+        for (const ModelVolume *model_volume : model_object->volumes) {
             check(model_volume->id());
+	        check(model_volume->config.id());
+        }
         for (const ModelInstance *model_instance : model_object->instances)
             check(model_instance->id());
     }
-    for (const auto mm : model.materials)
+    for (const auto mm : model.materials) {
         check(mm.second->id());
+        check(mm.second->config.id());
+    }
 }
 
 void check_model_ids_equal(const Model &model1, const Model &model2)
@@ -1892,10 +1911,13 @@ void check_model_ids_equal(const Model &model1, const Model &model2)
         const ModelObject &model_object1 = *model1.objects[idx_model];
         const ModelObject &model_object2 = *  model2.objects[idx_model];
         assert(model_object1.id() == model_object2.id());
+        assert(model_object1.config.id() == model_object2.config.id());
         assert(model_object1.volumes.size() == model_object2.volumes.size());
         assert(model_object1.instances.size() == model_object2.instances.size());
-        for (size_t i = 0; i < model_object1.volumes.size(); ++ i)
+        for (size_t i = 0; i < model_object1.volumes.size(); ++ i) {
             assert(model_object1.volumes[i]->id() == model_object2.volumes[i]->id());
+        	assert(model_object1.volumes[i]->config.id() == model_object2.volumes[i]->config.id());
+        }
         for (size_t i = 0; i < model_object1.instances.size(); ++ i)
             assert(model_object1.instances[i]->id() == model_object2.instances[i]->id());
     }
@@ -1906,9 +1928,22 @@ void check_model_ids_equal(const Model &model1, const Model &model2)
         for (; it1 != model1.materials.end(); ++ it1, ++ it2) {
             assert(it1->first == it2->first); // compare keys
             assert(it1->second->id() == it2->second->id());
+        	assert(it1->second->config.id() == it2->second->config.id());
         }
     }
 }
 #endif /* NDEBUG */
 
 }
+
+#if 0
+CEREAL_REGISTER_TYPE(Slic3r::ModelObject)
+CEREAL_REGISTER_TYPE(Slic3r::ModelVolume)
+CEREAL_REGISTER_TYPE(Slic3r::ModelInstance)
+CEREAL_REGISTER_TYPE(Slic3r::Model)
+
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ObjectBase, Slic3r::ModelObject)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ObjectBase, Slic3r::ModelVolume)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ObjectBase, Slic3r::ModelInstance)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::ObjectBase, Slic3r::Model)
+#endif
\ No newline at end of file
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index bac8ae507..7551bd8cb 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -2,19 +2,20 @@
 #define slic3r_Model_hpp_
 
 #include "libslic3r.h"
-#include "PrintConfig.hpp"
+#include "Geometry.hpp"
 #include "Layer.hpp"
+#include "ObjectID.hpp"
 #include "Point.hpp"
-#include "TriangleMesh.hpp"
+#include "PrintConfig.hpp"
 #include "Slicing.hpp"
+#include "SLA/SLACommon.hpp"
+#include "TriangleMesh.hpp"
 
 #include <map>
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>
-#include "Geometry.hpp"
-#include <libslic3r/SLA/SLACommon.hpp>
 
 namespace Slic3r {
 
@@ -26,83 +27,54 @@ class ModelVolume;
 class Print;
 class SLAPrint;
 
-typedef std::string t_model_material_id;
-typedef std::string t_model_material_attribute;
-typedef std::map<t_model_material_attribute, std::string> t_model_material_attributes;
-
-typedef std::map<t_model_material_id, ModelMaterial*> ModelMaterialMap;
-typedef std::vector<ModelObject*> ModelObjectPtrs;
-typedef std::vector<ModelVolume*> ModelVolumePtrs;
-typedef std::vector<ModelInstance*> ModelInstancePtrs;
-
-// Unique identifier of a Model, ModelObject, ModelVolume, ModelInstance or ModelMaterial.
-// Used to synchronize the front end (UI) with the back end (BackgroundSlicingProcess / Print / PrintObject)
-// Valid IDs are strictly positive (non zero).
-// It is declared as an object, as some compilers (notably msvcc) consider a typedef size_t equivalent to size_t
-// for parameter overload.
-struct ModelID 
-{
-	ModelID(size_t id) : id(id) {}
-
-	bool operator==(const ModelID &rhs) const { return this->id == rhs.id; }
-	bool operator!=(const ModelID &rhs) const { return this->id != rhs.id; }
-	bool operator< (const ModelID &rhs) const { return this->id <  rhs.id; }
-	bool operator> (const ModelID &rhs) const { return this->id >  rhs.id; }
-	bool operator<=(const ModelID &rhs) const { return this->id <= rhs.id; }
-	bool operator>=(const ModelID &rhs) const { return this->id >= rhs.id; }
-
-    bool valid() const { return id != 0; }
-
-	size_t	id;
-};
-
-// Unique object / instance ID for the wipe tower.
-extern ModelID wipe_tower_object_id();
-extern ModelID wipe_tower_instance_id();
+namespace UndoRedo {
+	class StackImpl;
+}
 
-// Base for Model, ModelObject, ModelVolume, ModelInstance or ModelMaterial to provide a unique ID
-// to synchronize the front end (UI) with the back end (BackgroundSlicingProcess / Print / PrintObject).
-// Achtung! The s_last_id counter is not thread safe, so it is expected, that the ModelBase derived instances
-// are only instantiated from the main thread.
-class ModelBase
+class ModelConfig : public ObjectBase, public DynamicPrintConfig
 {
-public:
-    ModelID     id() const { return m_id; }
+private:
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	friend class ModelObject;
+	friend class ModelVolume;
+	friend class ModelMaterial;
 
-protected:
     // Constructors to be only called by derived classes.
     // Default constructor to assign a unique ID.
-    ModelBase() : m_id(generate_new_id()) {}
+    explicit ModelConfig() {}
     // Constructor with ignored int parameter to assign an invalid ID, to be replaced
     // by an existing ID copied from elsewhere.
-    ModelBase(int) : m_id(ModelID(0)) {}
-
-    // Use with caution!
-    void        set_new_unique_id() { m_id = generate_new_id(); }
-    void        set_invalid_id()    { m_id = 0; }
-    // Use with caution!
-    void        copy_id(const ModelBase &rhs) { m_id = rhs.id(); }
-
-    // Override this method if a ModelBase derived class owns other ModelBase derived instances.
-    void        assign_new_unique_ids_recursive() { this->set_new_unique_id(); }
+    explicit ModelConfig(int) : ObjectBase(-1) {}
+    // Copy constructor copies the ID.
+	explicit ModelConfig(const ModelConfig &cfg) : ObjectBase(-1), DynamicPrintConfig(cfg) { this->copy_id(cfg); }
+    // Move constructor copies the ID.
+	explicit ModelConfig(ModelConfig &&cfg) : ObjectBase(-1), DynamicPrintConfig(std::move(cfg)) { this->copy_id(cfg); }
+
+	ModelConfig& operator=(const ModelConfig &rhs) = default;
+    ModelConfig& operator=(ModelConfig &&rhs) = default;
+
+	template<class Archive> void serialize(Archive &ar) {
+		ar(cereal::base_class<DynamicPrintConfig>(this));
+	}
+};
 
-private:
-    ModelID                 m_id;
+typedef std::string t_model_material_id;
+typedef std::string t_model_material_attribute;
+typedef std::map<t_model_material_attribute, std::string> t_model_material_attributes;
 
-	static inline ModelID   generate_new_id() { return ModelID(++ s_last_id); }
-    static size_t           s_last_id;
-	
-	friend ModelID wipe_tower_object_id();
-	friend ModelID wipe_tower_instance_id();
-};
+typedef std::map<t_model_material_id, ModelMaterial*> ModelMaterialMap;
+typedef std::vector<ModelObject*> ModelObjectPtrs;
+typedef std::vector<ModelVolume*> ModelVolumePtrs;
+typedef std::vector<ModelInstance*> ModelInstancePtrs;
 
-#define MODELBASE_DERIVED_COPY_MOVE_CLONE(TYPE) \
+#define OBJECTBASE_DERIVED_COPY_MOVE_CLONE(TYPE) \
     /* Copy a model, copy the IDs. The Print::apply() will call the TYPE::copy() method */ \
     /* to make a private copy for background processing. */ \
-    static TYPE* new_copy(const TYPE &rhs)  { return new TYPE(rhs); } \
-    static TYPE* new_copy(TYPE &&rhs)       { return new TYPE(std::move(rhs)); } \
-    static TYPE  make_copy(const TYPE &rhs) { return TYPE(rhs); } \
-    static TYPE  make_copy(TYPE &&rhs)      { return TYPE(std::move(rhs)); } \
+    static TYPE* new_copy(const TYPE &rhs)  { auto *ret = new TYPE(rhs); assert(ret->id() == rhs.id()); return ret; } \
+    static TYPE* new_copy(TYPE &&rhs)       { auto *ret = new TYPE(std::move(rhs)); assert(ret->id() == rhs.id()); return ret; } \
+    static TYPE  make_copy(const TYPE &rhs) { TYPE ret(rhs); assert(ret.id() == rhs.id()); return ret; } \
+    static TYPE  make_copy(TYPE &&rhs)      { TYPE ret(std::move(rhs)); assert(ret.id() == rhs.id()); return ret; } \
     TYPE&        assign_copy(const TYPE &rhs); \
     TYPE&        assign_copy(TYPE &&rhs); \
     /* Copy a TYPE, generate new IDs. The front end will use this call. */ \
@@ -110,52 +82,62 @@ private:
         /* Default constructor assigning an invalid ID. */ \
         auto obj = new TYPE(-1); \
         obj->assign_clone(rhs); \
+        assert(obj->id().valid() && obj->id() != rhs.id()); \
         return obj; \
 	} \
     TYPE         make_clone(const TYPE &rhs) { \
         /* Default constructor assigning an invalid ID. */ \
         TYPE obj(-1); \
         obj.assign_clone(rhs); \
+        assert(obj.id().valid() && obj.id() != rhs.id()); \
         return obj; \
     } \
     TYPE&        assign_clone(const TYPE &rhs) { \
         this->assign_copy(rhs); \
+        assert(this->id().valid() && this->id() == rhs.id()); \
         this->assign_new_unique_ids_recursive(); \
+        assert(this->id().valid() && this->id() != rhs.id()); \
 		return *this; \
     }
 
-#define MODELBASE_DERIVED_PRIVATE_COPY_MOVE(TYPE) \
-private: \
-    /* Private constructor with an unused int parameter will create a TYPE instance with an invalid ID. */ \
-    explicit TYPE(int) : ModelBase(-1) {}; \
-    void assign_new_unique_ids_recursive();
-
 // Material, which may be shared across multiple ModelObjects of a single Model.
-class ModelMaterial : public ModelBase
+class ModelMaterial final : public ObjectBase
 {
 public:
     // Attributes are defined by the AMF file format, but they don't seem to be used by Slic3r for any purpose.
     t_model_material_attributes attributes;
     // Dynamic configuration storage for the object specific configuration values, overriding the global configuration.
-    DynamicPrintConfig config;
+    ModelConfig config;
 
     Model* get_model() const { return m_model; }
     void apply(const t_model_material_attributes &attributes)
         { this->attributes.insert(attributes.begin(), attributes.end()); }
 
-protected:
-    friend class Model;
-	// Constructor, which assigns a new unique ID.
-	ModelMaterial(Model *model) : m_model(model) {}
-	// Copy constructor copies the ID and m_model!
-	ModelMaterial(const ModelMaterial &rhs) = default;
-	void set_model(Model *model) { m_model = model; }
-
 private:
     // Parent, owning this material.
     Model *m_model;
-    
-	ModelMaterial() = delete;
+
+    // To be accessed by the Model.
+    friend class Model;
+	// Constructor, which assigns a new unique ID to the material and to its config.
+	ModelMaterial(Model *model) : m_model(model) { assert(this->id().valid()); }
+	// Copy constructor copies the IDs of the ModelMaterial and its config, and m_model!
+	ModelMaterial(const ModelMaterial &rhs) = default;
+	void set_model(Model *model) { m_model = model; }
+	void set_new_unique_id() { ObjectBase::set_new_unique_id(); this->config.set_new_unique_id(); }
+
+	// To be accessed by the serialization and Undo/Redo code.
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	// Create an object for deserialization, don't allocate IDs for ModelMaterial and its config.
+	ModelMaterial() : ObjectBase(-1), config(-1), m_model(nullptr) { assert(this->id().invalid()); assert(this->config.id().invalid()); }
+	template<class Archive> void serialize(Archive &ar) { 
+		assert(this->id().invalid()); assert(this->config.id().invalid());
+		ar(attributes, config);
+		// assert(this->id().valid()); assert(this->config.id().valid());
+	}
+
+	// Disabled methods.
 	ModelMaterial(ModelMaterial &&rhs) = delete;
 	ModelMaterial& operator=(const ModelMaterial &rhs) = delete;
     ModelMaterial& operator=(ModelMaterial &&rhs) = delete;
@@ -165,9 +147,8 @@ private:
 // and possibly having multiple modifier volumes, each modifier volume with its set of parameters and materials.
 // Each ModelObject may be instantiated mutliple times, each instance having different placement on the print bed,
 // different rotation and different uniform scaling.
-class ModelObject : public ModelBase
+class ModelObject final : public ObjectBase
 {
-    friend class Model;
 public:
     std::string             name;
     std::string             input_file;    // XXX: consider fs::path
@@ -178,7 +159,7 @@ public:
     // ModelVolumes are owned by this ModelObject.
     ModelVolumePtrs         volumes;
     // Configuration parameters specific to a single ModelObject, overriding the global Slic3r settings.
-    DynamicPrintConfig      config;
+    ModelConfig      		config;
     // Variation of a layer thickness for spans of Z coordinates + optional parameter overrides.
     t_layer_config_ranges   layer_config_ranges;
     // Profile of increasing z to a layer height, to be linearly interpolated when calculating the layers.
@@ -264,7 +245,7 @@ public:
     void mirror(Axis axis);
 
     // This method could only be called before the meshes of this ModelVolumes are not shared!
-    void scale_mesh(const Vec3d& versor);
+    void scale_mesh_after_creation(const Vec3d& versor);
 
     size_t materials_count() const;
     size_t facets_count() const;
@@ -288,31 +269,53 @@ public:
 
     std::string get_export_filename() const;
 
-    // Get full stl statistics for all object's meshes 
+    // Get full stl statistics for all object's meshes
     stl_stats   get_object_stl_stats() const;
-    // Get count of errors in the mesh( or all object's meshes, if volume index isn't defined) 
+    // Get count of errors in the mesh( or all object's meshes, if volume index isn't defined)
     int         get_mesh_errors_count(const int vol_idx = -1) const;
 
-protected:
-    friend class Print;
-    friend class SLAPrint;
-    // Called by Print::apply() to set the model pointer after making a copy.
-    void        set_model(Model *model) { m_model = model; }
-
 private:
-    ModelObject(Model *model) : m_model(model), origin_translation(Vec3d::Zero()), 
-        m_bounding_box_valid(false), m_raw_bounding_box_valid(false), m_raw_mesh_bounding_box_valid(false) {}
-    ~ModelObject();
+    friend class Model;
+    // This constructor assigns new ID to this ModelObject and its config.
+	explicit ModelObject(Model *model) : m_model(model), origin_translation(Vec3d::Zero()),
+        m_bounding_box_valid(false), m_raw_bounding_box_valid(false), m_raw_mesh_bounding_box_valid(false)
+        { assert(this->id().valid()); }
+	explicit ModelObject(int) : ObjectBase(-1), config(-1), m_model(nullptr), origin_translation(Vec3d::Zero()), m_bounding_box_valid(false), m_raw_bounding_box_valid(false), m_raw_mesh_bounding_box_valid(false)
+		{ assert(this->id().invalid()); assert(this->config.id().invalid()); }
+	~ModelObject();
+	void assign_new_unique_ids_recursive() override;
 
-    /* To be able to return an object from own copy / clone methods. Hopefully the compiler will do the "Copy elision" */
-    /* (Omits copy and move(since C++11) constructors, resulting in zero - copy pass - by - value semantics). */
-    ModelObject(const ModelObject &rhs) : ModelBase(-1), m_model(rhs.m_model) { this->assign_copy(rhs); }
-    explicit ModelObject(ModelObject &&rhs) : ModelBase(-1) { this->assign_copy(std::move(rhs)); }
-    ModelObject& operator=(const ModelObject &rhs) { this->assign_copy(rhs); m_model = rhs.m_model; return *this; }
-    ModelObject& operator=(ModelObject &&rhs) { this->assign_copy(std::move(rhs)); m_model = rhs.m_model; return *this; }
+    // To be able to return an object from own copy / clone methods. Hopefully the compiler will do the "Copy elision"
+    // (Omits copy and move(since C++11) constructors, resulting in zero - copy pass - by - value semantics).
+    ModelObject(const ModelObject &rhs) : ObjectBase(-1), config(-1), m_model(rhs.m_model) { 
+    	assert(this->id().invalid()); assert(this->config.id().invalid()); assert(rhs.id() != rhs.config.id());
+    	this->assign_copy(rhs);
+    	assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+    	assert(this->id() == rhs.id()); assert(this->config.id() == rhs.config.id());
+    }
+    explicit ModelObject(ModelObject &&rhs) : ObjectBase(-1), config(-1) { 
+    	assert(this->id().invalid()); assert(this->config.id().invalid()); assert(rhs.id() != rhs.config.id());
+    	this->assign_copy(std::move(rhs));
+    	assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+    	assert(this->id() == rhs.id()); assert(this->config.id() == rhs.config.id());
+    }
+    ModelObject& operator=(const ModelObject &rhs) { 
+    	this->assign_copy(rhs); 
+    	m_model = rhs.m_model;
+    	assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+    	assert(this->id() == rhs.id()); assert(this->config.id() == rhs.config.id());
+    	return *this;
+    }
+    ModelObject& operator=(ModelObject &&rhs) { 
+    	this->assign_copy(std::move(rhs)); 
+    	m_model = rhs.m_model;
+    	assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+    	assert(this->id() == rhs.id()); assert(this->config.id() == rhs.config.id());
+    	return *this;
+    }
+	void set_new_unique_id() { ObjectBase::set_new_unique_id(); this->config.set_new_unique_id(); }
 
-    MODELBASE_DERIVED_COPY_MOVE_CLONE(ModelObject)
-	MODELBASE_DERIVED_PRIVATE_COPY_MOVE(ModelObject)
+    OBJECTBASE_DERIVED_COPY_MOVE_CLONE(ModelObject)
 
     // Parent object, owning this ModelObject. Set to nullptr here, so the macros above will have it initialized.
     Model                *m_model = nullptr;
@@ -323,7 +326,25 @@ private:
     mutable BoundingBoxf3 m_raw_bounding_box;
     mutable bool          m_raw_bounding_box_valid;
     mutable BoundingBoxf3 m_raw_mesh_bounding_box;
-    mutable bool          m_raw_mesh_bounding_box_valid;    
+    mutable bool          m_raw_mesh_bounding_box_valid;
+
+    // Called by Print::apply() to set the model pointer after making a copy.
+    friend class Print;
+    friend class SLAPrint;
+    void        set_model(Model *model) { m_model = model; }
+
+    // Undo / Redo through the cereal serialization library
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	// Used for deserialization -> Don't allocate any IDs for the ModelObject or its config.
+	ModelObject() : ObjectBase(-1), config(-1), m_model(nullptr), m_bounding_box_valid(false), m_raw_bounding_box_valid(false), m_raw_mesh_bounding_box_valid(false) {
+		assert(this->id().invalid()); assert(this->config.id().invalid());
+	}
+	template<class Archive> void serialize(Archive &ar) {
+		ar(cereal::base_class<ObjectBase>(this));
+		ar(name, input_file, instances, volumes, config, layer_config_ranges, layer_height_profile, sla_support_points, sla_points_status, origin_translation,
+			m_bounding_box, m_bounding_box_valid, m_raw_bounding_box, m_raw_bounding_box_valid, m_raw_mesh_bounding_box, m_raw_mesh_bounding_box_valid);
+	}
 };
 
 // Declared outside of ModelVolume, so it could be forward declared.
@@ -337,20 +358,20 @@ enum class ModelVolumeType : int {
 
 // An object STL, or a modifier volume, over which a different set of parameters shall be applied.
 // ModelVolume instances are owned by a ModelObject.
-class ModelVolume : public ModelBase
+class ModelVolume final : public ObjectBase
 {
 public:
     std::string         name;
     // The triangular model.
     const TriangleMesh& mesh() const { return *m_mesh.get(); }
-    void                set_mesh(const TriangleMesh &mesh) { m_mesh = std::make_shared<TriangleMesh>(mesh); }
-    void                set_mesh(TriangleMesh &&mesh) { m_mesh = std::make_shared<TriangleMesh>(std::move(mesh)); }
-    void                set_mesh(std::shared_ptr<TriangleMesh> &mesh) { m_mesh = mesh; }
-    void                set_mesh(std::unique_ptr<TriangleMesh> &&mesh) { m_mesh = std::move(mesh); }
-	void				reset_mesh() { m_mesh = std::make_shared<TriangleMesh>(); }
+    void                set_mesh(const TriangleMesh &mesh) { m_mesh = std::make_shared<const TriangleMesh>(mesh); }
+    void                set_mesh(TriangleMesh &&mesh) { m_mesh = std::make_shared<const TriangleMesh>(std::move(mesh)); }
+    void                set_mesh(std::shared_ptr<const TriangleMesh> &mesh) { m_mesh = mesh; }
+    void                set_mesh(std::unique_ptr<const TriangleMesh> &&mesh) { m_mesh = std::move(mesh); }
+	void				reset_mesh() { m_mesh = std::make_shared<const TriangleMesh>(); }
     // Configuration parameters specific to an object model geometry or a modifier volume, 
     // overriding the global Slic3r settings and the ModelObject settings.
-    DynamicPrintConfig  config;
+    ModelConfig  		config;
 
     // A parent object owning this modifier volume.
     ModelObject*        get_object() const { return this->object; };
@@ -385,7 +406,7 @@ public:
     void                mirror(Axis axis);
 
     // This method could only be called before the meshes of this ModelVolumes are not shared!
-    void                scale_geometry(const Vec3d& versor);
+    void                scale_geometry_after_creation(const Vec3d& versor);
 
     // Translates the mesh and the convex hull so that the origin of their vertices is in the center of this volume's bounding box.
     // Attention! This method may only be called just after ModelVolume creation! It must not be called once the TriangleMesh of this ModelVolume is shared!
@@ -431,66 +452,88 @@ public:
 
     const Transform3d& get_matrix(bool dont_translate = false, bool dont_rotate = false, bool dont_scale = false, bool dont_mirror = false) const { return m_transformation.get_matrix(dont_translate, dont_rotate, dont_scale, dont_mirror); }
 
-    using ModelBase::set_new_unique_id;
+	void set_new_unique_id() { ObjectBase::set_new_unique_id(); this->config.set_new_unique_id(); }
 
 protected:
 	friend class Print;
     friend class SLAPrint;
+    friend class Model;
 	friend class ModelObject;
 
+	// Copies IDs of both the ModelVolume and its config.
 	explicit ModelVolume(const ModelVolume &rhs) = default;
     void     set_model_object(ModelObject *model_object) { object = model_object; }
+	void 	 assign_new_unique_ids_recursive() override { ObjectBase::set_new_unique_id(); config.set_new_unique_id(); }
     void     transform_this_mesh(const Transform3d& t, bool fix_left_handed);
     void     transform_this_mesh(const Matrix3d& m, bool fix_left_handed);
 
 private:
     // Parent object owning this ModelVolume.
-    ModelObject*                    object;
+    ModelObject*                    	object;
     // The triangular model.
-    std::shared_ptr<TriangleMesh>   m_mesh;
+    std::shared_ptr<const TriangleMesh> m_mesh;
     // Is it an object to be printed, or a modifier volume?
-    ModelVolumeType                 m_type;
-    t_model_material_id             m_material_id;
+    ModelVolumeType                 	m_type;
+    t_model_material_id             	m_material_id;
     // The convex hull of this model's mesh.
-    std::shared_ptr<TriangleMesh>   m_convex_hull;
-    Geometry::Transformation        m_transformation;
+    std::shared_ptr<const TriangleMesh> m_convex_hull;
+    Geometry::Transformation        	m_transformation;
 
     // flag to optimize the checking if the volume is splittable
     //     -1   ->   is unknown value (before first cheking)
     //      0   ->   is not splittable
     //      1   ->   is splittable
-    mutable int               m_is_splittable{ -1 };
+    mutable int               		m_is_splittable{ -1 };
 
 	ModelVolume(ModelObject *object, const TriangleMesh &mesh) : m_mesh(new TriangleMesh(mesh)), m_type(ModelVolumeType::MODEL_PART), object(object)
     {
+		assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
         if (mesh.stl.stats.number_of_facets > 1)
             calculate_convex_hull();
     }
     ModelVolume(ModelObject *object, TriangleMesh &&mesh, TriangleMesh &&convex_hull) :
-		m_mesh(new TriangleMesh(std::move(mesh))), m_convex_hull(new TriangleMesh(std::move(convex_hull))), m_type(ModelVolumeType::MODEL_PART), object(object) {}
+		m_mesh(new TriangleMesh(std::move(mesh))), m_convex_hull(new TriangleMesh(std::move(convex_hull))), m_type(ModelVolumeType::MODEL_PART), object(object) {
+		assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+	}
 
     // Copying an existing volume, therefore this volume will get a copy of the ID assigned.
     ModelVolume(ModelObject *object, const ModelVolume &other) :
-        ModelBase(other), // copy the ID
+        ObjectBase(other),
         name(other.name), m_mesh(other.m_mesh), m_convex_hull(other.m_convex_hull), config(other.config), m_type(other.m_type), object(object), m_transformation(other.m_transformation)
     {
+		assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+		assert(this->id() == other.id() && this->config.id() == other.config.id());
         this->set_material_id(other.material_id());
     }
     // Providing a new mesh, therefore this volume will get a new unique ID assigned.
     ModelVolume(ModelObject *object, const ModelVolume &other, const TriangleMesh &&mesh) :
         name(other.name), m_mesh(new TriangleMesh(std::move(mesh))), config(other.config), m_type(other.m_type), object(object), m_transformation(other.m_transformation)
     {
+		assert(this->id().valid()); assert(this->config.id().valid()); assert(this->id() != this->config.id());
+		assert(this->id() != other.id() && this->config.id() == other.config.id());
         this->set_material_id(other.material_id());
+        this->config.set_new_unique_id();
         if (mesh.stl.stats.number_of_facets > 1)
             calculate_convex_hull();
+		assert(this->config.id().valid()); assert(this->config.id() != other.config.id()); assert(this->id() != this->config.id());
     }
 
     ModelVolume& operator=(ModelVolume &rhs) = delete;
+
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	// Used for deserialization, therefore no IDs are allocated.
+	ModelVolume() : ObjectBase(-1), config(-1), object(nullptr) {
+		assert(this->id().invalid()); assert(this->config.id().invalid());
+	}
+	template<class Archive> void serialize(Archive &ar) {
+		ar(name, config, m_mesh, m_type, m_material_id, m_convex_hull, m_transformation, m_is_splittable);
+	}
 };
 
 // A single instance of a ModelObject.
 // Knows the affine transformation of an object.
-class ModelInstance : public ModelBase
+class ModelInstance final : public ObjectBase
 {
 public:
     enum EPrintVolumeState : unsigned char
@@ -556,6 +599,7 @@ public:
 protected:
     friend class Print;
     friend class SLAPrint;
+    friend class Model;
     friend class ModelObject;
 
     explicit ModelInstance(const ModelInstance &rhs) = default;
@@ -566,15 +610,22 @@ private:
     ModelObject* object;
 
     // Constructor, which assigns a new unique ID.
-    explicit ModelInstance(ModelObject *object) : object(object), print_volume_state(PVS_Inside) {}
+    explicit ModelInstance(ModelObject *object) : object(object), print_volume_state(PVS_Inside) { assert(this->id().valid()); }
     // Constructor, which assigns a new unique ID.
     explicit ModelInstance(ModelObject *object, const ModelInstance &other) :
-        m_transformation(other.m_transformation), object(object), print_volume_state(PVS_Inside) {}
+        m_transformation(other.m_transformation), object(object), print_volume_state(PVS_Inside) { assert(this->id().valid() && this->id() != other.id()); }
 
-    ModelInstance() = delete;
     explicit ModelInstance(ModelInstance &&rhs) = delete;
     ModelInstance& operator=(const ModelInstance &rhs) = delete;
     ModelInstance& operator=(ModelInstance &&rhs) = delete;
+
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	// Used for deserialization, therefore no IDs are allocated.
+	ModelInstance() : ObjectBase(-1), object(nullptr) { assert(this->id().invalid()); }
+	template<class Archive> void serialize(Archive &ar) {
+		ar(m_transformation, print_volume_state);
+	}
 };
 
 // The print bed content.
@@ -582,7 +633,7 @@ private:
 // and with multiple modifier meshes.
 // A model groups multiple objects, each object having possibly multiple instances,
 // all objects may share mutliple materials.
-class Model : public ModelBase
+class Model final : public ObjectBase
 {
     static unsigned int s_auto_extruder_id;
 
@@ -594,17 +645,17 @@ public:
     ModelObjectPtrs     objects;
     
     // Default constructor assigns a new ID to the model.
-    Model() {}
+    Model() { assert(this->id().valid()); }
     ~Model() { this->clear_objects(); this->clear_materials(); }
 
-    // To be able to return an object from own copy / clone methods. Hopefully the compiler will do the "Copy elision"
-    // (Omits copy and move(since C++11) constructors, resulting in zero - copy pass - by - value semantics).
-    Model(const Model &rhs) : ModelBase(-1) { this->assign_copy(rhs); }
-    explicit Model(Model &&rhs) : ModelBase(-1) { this->assign_copy(std::move(rhs)); }
-    Model& operator=(const Model &rhs) { this->assign_copy(rhs); return *this; }
-    Model& operator=(Model &&rhs) { this->assign_copy(std::move(rhs)); return *this; }
+    /* To be able to return an object from own copy / clone methods. Hopefully the compiler will do the "Copy elision" */
+    /* (Omits copy and move(since C++11) constructors, resulting in zero - copy pass - by - value semantics). */
+    Model(const Model &rhs) : ObjectBase(-1) { assert(this->id().invalid()); this->assign_copy(rhs); assert(this->id().valid()); assert(this->id() == rhs.id()); }
+    explicit Model(Model &&rhs) : ObjectBase(-1) { assert(this->id().invalid()); this->assign_copy(std::move(rhs)); assert(this->id().valid()); assert(this->id() == rhs.id()); }
+    Model& operator=(const Model &rhs) { this->assign_copy(rhs); assert(this->id().valid()); assert(this->id() == rhs.id()); return *this; }
+    Model& operator=(Model &&rhs) { this->assign_copy(std::move(rhs)); assert(this->id().valid()); assert(this->id() == rhs.id()); return *this; }
 
-    MODELBASE_DERIVED_COPY_MOVE_CLONE(Model)
+    OBJECTBASE_DERIVED_COPY_MOVE_CLONE(Model)
 
     static Model read_from_file(const std::string &input_file, DynamicPrintConfig *config = nullptr, bool add_default_instances = true);
     static Model read_from_archive(const std::string &input_file, DynamicPrintConfig *config, bool add_default_instances = true);
@@ -615,7 +666,7 @@ public:
     ModelObject* add_object(const char *name, const char *path, TriangleMesh &&mesh);
     ModelObject* add_object(const ModelObject &other);
     void         delete_object(size_t idx);
-    bool         delete_object(ModelID id);
+    bool         delete_object(ObjectID id);
     bool         delete_object(ModelObject* object);
     void         clear_objects();
 
@@ -633,24 +684,24 @@ public:
     BoundingBoxf3 bounding_box() const;
     // Set the print_volume_state of PrintObject::instances, 
     // return total number of printable objects.
-    unsigned int update_print_volume_state(const BoundingBoxf3 &print_volume);
+    unsigned int  update_print_volume_state(const BoundingBoxf3 &print_volume);
 	// Returns true if any ModelObject was modified.
-    bool center_instances_around_point(const Vec2d &point);
-    void translate(coordf_t x, coordf_t y, coordf_t z) { for (ModelObject *o : this->objects) o->translate(x, y, z); }
-    TriangleMesh mesh() const;
-    bool arrange_objects(coordf_t dist, const BoundingBoxf* bb = NULL);
+    bool 		  center_instances_around_point(const Vec2d &point);
+    void 		  translate(coordf_t x, coordf_t y, coordf_t z) { for (ModelObject *o : this->objects) o->translate(x, y, z); }
+    TriangleMesh  mesh() const;
+    bool 		  arrange_objects(coordf_t dist, const BoundingBoxf* bb = NULL);
     // Croaks if the duplicated objects do not fit the print bed.
-    void duplicate(size_t copies_num, coordf_t dist, const BoundingBoxf* bb = NULL);
-    void duplicate_objects(size_t copies_num, coordf_t dist, const BoundingBoxf* bb = NULL);
-    void duplicate_objects_grid(size_t x, size_t y, coordf_t dist);
+    void 		  duplicate(size_t copies_num, coordf_t dist, const BoundingBoxf* bb = NULL);
+    void 	      duplicate_objects(size_t copies_num, coordf_t dist, const BoundingBoxf* bb = NULL);
+    void 		  duplicate_objects_grid(size_t x, size_t y, coordf_t dist);
 
-    bool looks_like_multipart_object() const;
-    void convert_multipart_object(unsigned int max_extruders);
+    bool 		  looks_like_multipart_object() const;
+    void 		  convert_multipart_object(unsigned int max_extruders);
 
     // Ensures that the min z of the model is not negative
-    void adjust_min_z();
+    void 		  adjust_min_z();
 
-    void print_info() const { for (const ModelObject *o : this->objects) o->print_info(); }
+    void 		  print_info() const { for (const ModelObject *o : this->objects) o->print_info(); }
 
     static unsigned int get_auto_extruder_id(unsigned int max_extruders);
     static std::string get_auto_extruder_id_as_string(unsigned int max_extruders);
@@ -662,11 +713,19 @@ public:
     std::string         propose_export_file_name_and_path(const std::string &new_extension) const;
 
 private:
-    MODELBASE_DERIVED_PRIVATE_COPY_MOVE(Model)
+	explicit Model(int) : ObjectBase(-1) { assert(this->id().invalid()); };
+	void assign_new_unique_ids_recursive();
+	void update_links_bottom_up_recursive();
+
+	friend class cereal::access;
+	friend class UndoRedo::StackImpl;
+	template<class Archive> void serialize(Archive &ar) {
+		ar(materials, objects);
+	}
 };
 
-#undef MODELBASE_DERIVED_COPY_MOVE_CLONE
-#undef MODELBASE_DERIVED_PRIVATE_COPY_MOVE
+#undef OBJECTBASE_DERIVED_COPY_MOVE_CLONE
+#undef OBJECTBASE_DERIVED_PRIVATE_COPY_MOVE
 
 // Test whether the two models contain the same number of ModelObjects with the same set of IDs
 // ordered in the same order. In that case it is not necessary to kill the background processing.
@@ -686,6 +745,6 @@ void check_model_ids_validity(const Model &model);
 void check_model_ids_equal(const Model &model1, const Model &model2);
 #endif /* NDEBUG */
 
-}
+} // namespace Slic3r
 
-#endif
+#endif /* slic3r_Model_hpp_ */
diff --git a/src/libslic3r/ObjectID.cpp b/src/libslic3r/ObjectID.cpp
new file mode 100644
index 000000000..b188d84c0
--- /dev/null
+++ b/src/libslic3r/ObjectID.cpp
@@ -0,0 +1,22 @@
+#include "ObjectID.hpp"
+
+namespace Slic3r {
+
+size_t ObjectBase::s_last_id = 0;
+
+// Unique object / instance ID for the wipe tower.
+ObjectID wipe_tower_object_id()
+{
+    static ObjectBase mine;
+    return mine.id();
+}
+
+ObjectID wipe_tower_instance_id()
+{
+    static ObjectBase mine;
+    return mine.id();
+}
+
+} // namespace Slic3r
+
+// CEREAL_REGISTER_TYPE(Slic3r::ObjectBase)
diff --git a/src/libslic3r/ObjectID.hpp b/src/libslic3r/ObjectID.hpp
new file mode 100644
index 000000000..484d1173b
--- /dev/null
+++ b/src/libslic3r/ObjectID.hpp
@@ -0,0 +1,93 @@
+#ifndef slic3r_ObjectID_hpp_
+#define slic3r_ObjectID_hpp_
+
+#include <cereal/access.hpp>
+
+namespace Slic3r {
+
+namespace UndoRedo {
+	class StackImpl;
+};
+
+// Unique identifier of a mutable object accross the application.
+// Used to synchronize the front end (UI) with the back end (BackgroundSlicingProcess / Print / PrintObject)
+// (for Model, ModelObject, ModelVolume, ModelInstance or ModelMaterial classes)
+// and to serialize / deserialize an object onto the Undo / Redo stack.
+// Valid IDs are strictly positive (non zero).
+// It is declared as an object, as some compilers (notably msvcc) consider a typedef size_t equivalent to size_t
+// for parameter overload.
+class ObjectID
+{
+public:
+	ObjectID(size_t id) : id(id) {}
+	// Default constructor constructs an invalid ObjectID.
+	ObjectID() : id(0) {}
+
+	bool operator==(const ObjectID &rhs) const { return this->id == rhs.id; }
+	bool operator!=(const ObjectID &rhs) const { return this->id != rhs.id; }
+	bool operator< (const ObjectID &rhs) const { return this->id <  rhs.id; }
+	bool operator> (const ObjectID &rhs) const { return this->id >  rhs.id; }
+	bool operator<=(const ObjectID &rhs) const { return this->id <= rhs.id; }
+	bool operator>=(const ObjectID &rhs) const { return this->id >= rhs.id; }
+
+    bool valid() const { return id != 0; }
+    bool invalid() const { return id == 0; }
+
+	size_t	id;
+
+private:
+	friend class cereal::access;
+	template<class Archive> void serialize(Archive &ar) { ar(id); }
+};
+
+// Base for Model, ModelObject, ModelVolume, ModelInstance or ModelMaterial to provide a unique ID
+// to synchronize the front end (UI) with the back end (BackgroundSlicingProcess / Print / PrintObject).
+// Achtung! The s_last_id counter is not thread safe, so it is expected, that the ObjectBase derived instances
+// are only instantiated from the main thread.
+class ObjectBase
+{
+public:
+    ObjectID     id() const { return m_id; }
+
+protected:
+    // Constructors to be only called by derived classes.
+    // Default constructor to assign a unique ID.
+    ObjectBase() : m_id(generate_new_id()) {}
+    // Constructor with ignored int parameter to assign an invalid ID, to be replaced
+    // by an existing ID copied from elsewhere.
+    ObjectBase(int) : m_id(ObjectID(0)) {}
+	// The class tree will have virtual tables and type information.
+	virtual ~ObjectBase() {}
+
+    // Use with caution!
+    void        set_new_unique_id() { m_id = generate_new_id(); }
+    void        set_invalid_id()    { m_id = 0; }
+    // Use with caution!
+    void        copy_id(const ObjectBase &rhs) { m_id = rhs.id(); }
+
+    // Override this method if a ObjectBase derived class owns other ObjectBase derived instances.
+    virtual void assign_new_unique_ids_recursive() { this->set_new_unique_id(); }
+
+private:
+    ObjectID                m_id;
+
+	static inline ObjectID  generate_new_id() { return ObjectID(++ s_last_id); }
+    static size_t           s_last_id;
+	
+	friend ObjectID wipe_tower_object_id();
+	friend ObjectID wipe_tower_instance_id();
+
+	friend class cereal::access;
+	friend class Slic3r::UndoRedo::StackImpl;
+	template<class Archive> void serialize(Archive &ar) { ar(m_id); }
+    ObjectBase(const ObjectID id) : m_id(id) {}
+  	template<class Archive> static void load_and_construct(Archive & ar, cereal::construct<ObjectBase> &construct) { ObjectID id; ar(id); construct(id); }
+};
+
+// Unique object / instance ID for the wipe tower.
+extern ObjectID wipe_tower_object_id();
+extern ObjectID wipe_tower_instance_id();
+
+} // namespace Slic3r
+
+#endif /* slic3r_ObjectID_hpp_ */
diff --git a/src/libslic3r/Point.hpp b/src/libslic3r/Point.hpp
index b02ead299..994f45e59 100644
--- a/src/libslic3r/Point.hpp
+++ b/src/libslic3r/Point.hpp
@@ -62,8 +62,8 @@ inline Vec2i64 to_2d(const Vec3i64 &pt3) { return Vec2i64(pt3(0), pt3(1)); }
 inline Vec2f   to_2d(const Vec3f   &pt3) { return Vec2f  (pt3(0), pt3(1)); }
 inline Vec2d   to_2d(const Vec3d   &pt3) { return Vec2d  (pt3(0), pt3(1)); }
 
-inline Vec3d to_3d(const Vec2d &v, double z) { return Vec3d(v(0), v(1), z); }
-inline Vec3f to_3d(const Vec2f &v, float z) { return Vec3f(v(0), v(1), z); }
+inline Vec3d   to_3d(const Vec2d &v, double z) { return Vec3d(v(0), v(1), z); }
+inline Vec3f   to_3d(const Vec2f &v, float z) { return Vec3f(v(0), v(1), z); }
 inline Vec3i64 to_3d(const Vec2i64 &v, float z) { return Vec3i64(int64_t(v(0)), int64_t(v(1)), int64_t(z)); }
 inline Vec3crd to_3d(const Vec3crd &p, coord_t z) { return Vec3crd(p(0), p(1), z); }
 
@@ -291,4 +291,21 @@ namespace boost { namespace polygon {
 } }
 // end Boost
 
+// Serialization through the Cereal library
+namespace cereal {
+//	template<class Archive> void serialize(Archive& archive, Slic3r::Vec2crd &v) { archive(v.x(), v.y()); }
+//	template<class Archive> void serialize(Archive& archive, Slic3r::Vec3crd &v) { archive(v.x(), v.y(), v.z()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec2i   &v) { archive(v.x(), v.y()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec3i   &v) { archive(v.x(), v.y(), v.z()); }
+//	template<class Archive> void serialize(Archive& archive, Slic3r::Vec2i64 &v) { archive(v.x(), v.y()); }
+//	template<class Archive> void serialize(Archive& archive, Slic3r::Vec3i64 &v) { archive(v.x(), v.y(), v.z()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec2f   &v) { archive(v.x(), v.y()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec3f   &v) { archive(v.x(), v.y(), v.z()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec2d   &v) { archive(v.x(), v.y()); }
+	template<class Archive> void serialize(Archive& archive, Slic3r::Vec3d   &v) { archive(v.x(), v.y(), v.z()); }
+
+	template<class Archive> void load(Archive& archive, Slic3r::Matrix2f &m) { archive.loadBinary((char*)m.data(), sizeof(float) * 4); }
+	template<class Archive> void save(Archive& archive, Slic3r::Matrix2f &m) { archive.saveBinary((char*)m.data(), sizeof(float) * 4); }
+}
+
 #endif
diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index 7034d8dc0..a1e31c26c 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -392,7 +392,7 @@ static inline void model_volume_list_copy_configs(ModelObject &model_object_dst,
         assert(mv_src.id() == mv_dst.id());
         // Copy the ModelVolume data.
         mv_dst.name   = mv_src.name;
-        mv_dst.config = mv_src.config;
+		static_cast<DynamicPrintConfig&>(mv_dst.config) = static_cast<const DynamicPrintConfig&>(mv_src.config);
         //FIXME what to do with the materials?
         // mv_dst.m_material_id = mv_src.m_material_id;
         ++ i_src;
@@ -587,10 +587,10 @@ Print::ApplyStatus Print::apply(const Model &model, const DynamicPrintConfig &co
             Moved,
             Deleted,
         };
-        ModelObjectStatus(ModelID id, Status status = Unknown) : id(id), status(status) {}
-        ModelID     id;
-        Status      status;
-        LayerRanges layer_ranges;
+        ModelObjectStatus(ObjectID id, Status status = Unknown) : id(id), status(status) {}
+		ObjectID     id;
+        Status       status;
+        LayerRanges  layer_ranges;
         // Search by id.
         bool operator<(const ModelObjectStatus &rhs) const { return id < rhs.id; }
     };
@@ -695,9 +695,9 @@ Print::ApplyStatus Print::apply(const Model &model, const DynamicPrintConfig &co
             print_object(print_object),
             trafo(print_object->trafo()),
             status(status) {}
-        PrintObjectStatus(ModelID id) : id(id), print_object(nullptr), trafo(Transform3d::Identity()), status(Unknown) {}
+        PrintObjectStatus(ObjectID id) : id(id), print_object(nullptr), trafo(Transform3d::Identity()), status(Unknown) {}
         // ID of the ModelObject & PrintObject
-        ModelID          id;
+        ObjectID          id;
         // Pointer to the old PrintObject
         PrintObject     *print_object;
         // Trafo generated with model_object->world_matrix(true) 
@@ -757,7 +757,7 @@ Print::ApplyStatus Print::apply(const Model &model, const DynamicPrintConfig &co
             // Synchronize Object's config.
             bool object_config_changed = model_object.config != model_object_new.config;
 			if (object_config_changed)
-                model_object.config = model_object_new.config;
+				static_cast<DynamicPrintConfig&>(model_object.config) = static_cast<const DynamicPrintConfig&>(model_object_new.config);
             if (! object_diff.empty() || object_config_changed) {
                 PrintObjectConfig new_config = PrintObject::object_config_from_model_object(m_default_object_config, model_object, num_extruders);
                 auto range = print_object_status.equal_range(PrintObjectStatus(model_object.id()));
diff --git a/src/libslic3r/PrintBase.hpp b/src/libslic3r/PrintBase.hpp
index d4c39499c..d84d492a0 100644
--- a/src/libslic3r/PrintBase.hpp
+++ b/src/libslic3r/PrintBase.hpp
@@ -246,7 +246,7 @@ public:
     struct TaskParams {
 		TaskParams() : single_model_object(0), single_model_instance_only(false), to_object_step(-1), to_print_step(-1) {}
         // If non-empty, limit the processing to this ModelObject.
-        ModelID                 single_model_object;
+        ObjectID                single_model_object;
 		// If set, only process single_model_object. Otherwise process everything, but single_model_object first.
 		bool					single_model_instance_only;
         // If non-negative, stop processing at the successive object step.
diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index f159ea7b7..979d9b46e 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -406,10 +406,13 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipRectilinear));
 
     def = this->add("bottom_fill_pattern", coEnum);
-    *def = *def_top_fill_pattern;
     def->label = L("Bottom fill pattern");
+    def->category = L("Infill");
     def->tooltip = L("Fill pattern for bottom infill. This only affects the bottom external visible layer, and not its adjacent solid shells.");
     def->cli = "bottom-fill-pattern|external-fill-pattern|solid-fill-pattern";
+    def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
+    def->enum_values = def_top_fill_pattern->enum_values;
+    def->aliases = def_top_fill_pattern->aliases;
     def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipRectilinear));
 
     def = this->add("external_perimeter_extrusion_width", coFloatOrPercent);
@@ -3250,3 +3253,7 @@ void DynamicPrintAndCLIConfig::handle_legacy(t_config_option_key &opt_key, std::
 }
 
 }
+
+#include <cereal/types/polymorphic.hpp>
+CEREAL_REGISTER_TYPE(Slic3r::DynamicPrintConfig)
+CEREAL_REGISTER_POLYMORPHIC_RELATION(Slic3r::DynamicConfig, Slic3r::DynamicPrintConfig) 
diff --git a/src/libslic3r/PrintConfig.hpp b/src/libslic3r/PrintConfig.hpp
index 3bf5c5af7..5731bef00 100644
--- a/src/libslic3r/PrintConfig.hpp
+++ b/src/libslic3r/PrintConfig.hpp
@@ -1218,6 +1218,8 @@ private:
             this->options.insert(cli_actions_config_def.options.begin(), cli_actions_config_def.options.end());
             this->options.insert(cli_transform_config_def.options.begin(), cli_transform_config_def.options.end());
             this->options.insert(cli_misc_config_def.options.begin(), cli_misc_config_def.options.end());
+            for (const auto &kvp : this->options)
+            	this->by_serialization_key_ordinal[kvp.second.serialization_key_ordinal] = &kvp.second;
         }
         // Do not release the default values, they are handled by print_config_def & cli_actions_config_def / cli_transform_config_def / cli_misc_config_def.
         ~PrintAndCLIConfigDef() { this->options.clear(); }
@@ -1227,4 +1229,38 @@ private:
 
 } // namespace Slic3r
 
+// Serialization through the Cereal library
+namespace cereal {
+	// Let cereal know that there are load / save non-member functions declared for DynamicPrintConfig, ignore serialize / load / save from parent class DynamicConfig.
+	template <class Archive> struct specialize<Archive, Slic3r::DynamicPrintConfig, cereal::specialization::non_member_load_save> {};
+
+	template<class Archive> void load(Archive& archive, Slic3r::DynamicPrintConfig &config) 
+	{
+		size_t cnt;
+		archive(cnt);
+		config.clear();
+		for (size_t i = 0; i < cnt; ++ i) {
+			size_t serialization_key_ordinal;
+			archive(serialization_key_ordinal);
+			assert(serialization_key_ordinal > 0);
+			auto it = Slic3r::print_config_def.by_serialization_key_ordinal.find(serialization_key_ordinal);
+			assert(it != Slic3r::print_config_def.by_serialization_key_ordinal.end());
+			config.set_key_value(it->second->opt_key, it->second->load_option_from_archive(archive));
+		}
+	}
+
+	template<class Archive> void save(Archive& archive, const Slic3r::DynamicPrintConfig &config)
+	{
+		size_t cnt = config.size();
+		archive(cnt);
+		for (auto it = config.cbegin(); it != config.cend(); ++it) {
+			const Slic3r::ConfigOptionDef* optdef = Slic3r::print_config_def.get(it->first);
+			assert(optdef != nullptr);
+			assert(optdef->serialization_key_ordinal > 0);
+			archive(optdef->serialization_key_ordinal);
+			optdef->save_option_to_archive(archive, it->second.get());
+		}
+	}
+}
+
 #endif
diff --git a/src/libslic3r/SLA/SLACommon.hpp b/src/libslic3r/SLA/SLACommon.hpp
index eb986a259..874388e05 100644
--- a/src/libslic3r/SLA/SLACommon.hpp
+++ b/src/libslic3r/SLA/SLACommon.hpp
@@ -43,6 +43,8 @@ struct SupportPoint {
 
     bool operator==(const SupportPoint& sp) const { return (pos==sp.pos) && head_front_radius==sp.head_front_radius && is_new_island==sp.is_new_island; }
     bool operator!=(const SupportPoint& sp) const { return !(sp == (*this)); }
+
+	template<class Archive> void serialize(Archive &ar) { ar(pos, head_front_radius, is_new_island); }
 };
 
 /// An index-triangle structure for libIGL functions. Also serves as an
diff --git a/src/libslic3r/SLAPrint.cpp b/src/libslic3r/SLAPrint.cpp
index 2ae1d7af8..fb2a5d7df 100644
--- a/src/libslic3r/SLAPrint.cpp
+++ b/src/libslic3r/SLAPrint.cpp
@@ -211,8 +211,8 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
             Moved,
             Deleted,
         };
-        ModelObjectStatus(ModelID id, Status status = Unknown) : id(id), status(status) {}
-        ModelID                 id;
+        ModelObjectStatus(ObjectID id, Status status = Unknown) : id(id), status(status) {}
+        ObjectID                id;
         Status                  status;
         // Search by id.
         bool operator<(const ModelObjectStatus &rhs) const { return id < rhs.id; }
@@ -315,9 +315,9 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
             print_object(print_object),
             trafo(print_object->trafo()),
             status(status) {}
-        PrintObjectStatus(ModelID id) : id(id), print_object(nullptr), trafo(Transform3d::Identity()), status(Unknown) {}
+        PrintObjectStatus(ObjectID id) : id(id), print_object(nullptr), trafo(Transform3d::Identity()), status(Unknown) {}
         // ID of the ModelObject & PrintObject
-        ModelID          id;
+        ObjectID         id;
         // Pointer to the old PrintObject
         SLAPrintObject  *print_object;
         // Trafo generated with model_object->world_matrix(true)
@@ -367,7 +367,7 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
                 // Synchronize Object's config.
                 bool object_config_changed = model_object.config != model_object_new.config;
                 if (object_config_changed)
-                    model_object.config = model_object_new.config;
+					static_cast<DynamicPrintConfig&>(model_object.config) = static_cast<const DynamicPrintConfig&>(model_object_new.config);
                 if (! object_diff.empty() || object_config_changed) {
                     SLAPrintObjectConfig new_config = m_default_object_config;
                     normalize_and_apply_config(new_config, model_object.config);
diff --git a/src/libslic3r/SLAPrint.hpp b/src/libslic3r/SLAPrint.hpp
index b0c5a8fdc..9620e9b68 100644
--- a/src/libslic3r/SLAPrint.hpp
+++ b/src/libslic3r/SLAPrint.hpp
@@ -54,10 +54,10 @@ public:
     bool                        is_left_handed() const { return m_left_handed; }
 
     struct Instance {
-        Instance(ModelID instance_id, const Point &shift, float rotation) : instance_id(instance_id), shift(shift), rotation(rotation) {}
+        Instance(ObjectID instance_id, const Point &shift, float rotation) : instance_id(instance_id), shift(shift), rotation(rotation) {}
         bool operator==(const Instance &rhs) const { return this->instance_id == rhs.instance_id && this->shift == rhs.shift && this->rotation == rhs.rotation; }
         // ID of the corresponding ModelInstance.
-        ModelID instance_id;
+        ObjectID instance_id;
         // Slic3r::Point objects in scaled G-code coordinates
         Point 	shift;
         // Rotation along the Z axis, in radians.
diff --git a/src/libslic3r/Slicing.hpp b/src/libslic3r/Slicing.hpp
index 7ebb3f329..064363ec2 100644
--- a/src/libslic3r/Slicing.hpp
+++ b/src/libslic3r/Slicing.hpp
@@ -175,4 +175,9 @@ extern int generate_layer_height_texture(
 
 }; // namespace Slic3r
 
+namespace cereal
+{
+	template<class Archive> void serialize(Archive& archive, Slic3r::t_layer_height_range &lhr) { archive(lhr.first, lhr.second); }
+}
+
 #endif /* slic3r_Slicing_hpp_ */
diff --git a/src/libslic3r/TriangleMesh.hpp b/src/libslic3r/TriangleMesh.hpp
index 054a98935..5dd2597a5 100644
--- a/src/libslic3r/TriangleMesh.hpp
+++ b/src/libslic3r/TriangleMesh.hpp
@@ -195,4 +195,24 @@ TriangleMesh make_sphere(double rho, double fa=(2*PI/360));
 
 }
 
+// Serialization through the Cereal library
+#include <cereal/access.hpp>
+namespace cereal {
+	template <class Archive> struct specialize<Archive, Slic3r::TriangleMesh, cereal::specialization::non_member_load_save> {};
+	template<class Archive> void load(Archive &archive, Slic3r::TriangleMesh &mesh) {
+        stl_file &stl = mesh.stl;
+        stl.stats.type = inmemory;
+		archive(stl.stats.number_of_facets, stl.stats.original_num_facets);
+        stl_allocate(&stl);
+		archive.loadBinary((char*)stl.facet_start.data(), stl.facet_start.size() * 50);
+        stl_get_size(&stl);
+        mesh.repair();
+	}
+	template<class Archive> void save(Archive &archive, const Slic3r::TriangleMesh &mesh) {
+		const stl_file& stl = mesh.stl;
+		archive(stl.stats.number_of_facets, stl.stats.original_num_facets);
+		archive.saveBinary((char*)stl.facet_start.data(), stl.facet_start.size() * 50);
+	}
+}
+
 #endif
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index adf7f57a7..3b30e981c 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -182,7 +182,7 @@ class ScopeGuard
 public:
     typedef std::function<void()> Closure;
 private:
-    bool committed;
+//    bool committed;
     Closure closure;
 
 public:
diff --git a/src/libslic3r/pchheader.hpp b/src/libslic3r/pchheader.hpp
index b27dfe6a2..c0ffe2108 100644
--- a/src/libslic3r/pchheader.hpp
+++ b/src/libslic3r/pchheader.hpp
@@ -100,7 +100,10 @@
 #include <tbb/task_scheduler_init.h>
 
 #include <Eigen/Dense>
-#include <Eigen/Geometry> 
+#include <Eigen/Geometry>
+
+#include <cereal/access.hpp>
+#include <cereal/types/base_class.hpp>
 
 #include "BoundingBox.hpp"
 #include "ClipperUtils.hpp"
diff --git a/src/slic3r/CMakeLists.txt b/src/slic3r/CMakeLists.txt
index 13f563fd0..e3a910d6d 100644
--- a/src/slic3r/CMakeLists.txt
+++ b/src/slic3r/CMakeLists.txt
@@ -148,6 +148,8 @@ set(SLIC3R_GUI_SOURCES
     Utils/PresetUpdater.hpp
     Utils/Time.cpp
     Utils/Time.hpp
+    Utils/UndoRedo.cpp
+    Utils/UndoRedo.hpp
     Utils/HexFile.cpp
     Utils/HexFile.hpp
 )
@@ -161,7 +163,7 @@ endif ()
 
 add_library(libslic3r_gui STATIC ${SLIC3R_GUI_SOURCES})
 
-target_link_libraries(libslic3r_gui libslic3r avrdude imgui ${GLEW_LIBRARIES})
+target_link_libraries(libslic3r_gui libslic3r avrdude cereal imgui ${GLEW_LIBRARIES})
 if (SLIC3R_PCH AND NOT SLIC3R_SYNTAXONLY)
     add_precompiled_header(libslic3r_gui pchheader.hpp FORCEINCLUDE)
 endif ()
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index 64a734f81..c2948c262 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -1188,6 +1188,8 @@ wxDEFINE_EVENT(EVT_GLCANVAS_TAB, SimpleEvent);
 wxDEFINE_EVENT(EVT_GLCANVAS_RESETGIZMOS, SimpleEvent);
 wxDEFINE_EVENT(EVT_GLCANVAS_MOVE_DOUBLE_SLIDER, wxKeyEvent);
 wxDEFINE_EVENT(EVT_GLCANVAS_EDIT_COLOR_CHANGE, wxKeyEvent);
+wxDEFINE_EVENT(EVT_GLCANVAS_UNDO, SimpleEvent);
+wxDEFINE_EVENT(EVT_GLCANVAS_REDO, SimpleEvent);
 
 GLCanvas3D::GLCanvas3D(wxGLCanvas* canvas, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar)
     : m_canvas(canvas)
@@ -1791,7 +1793,7 @@ std::vector<int> GLCanvas3D::load_object(const Model& model, int obj_idx)
 void GLCanvas3D::mirror_selection(Axis axis)
 {
     m_selection.mirror(axis);
-    do_mirror();
+    do_mirror("Mirror Object");
     wxGetApp().obj_manipul()->set_dirty();
 }
 
@@ -1812,14 +1814,14 @@ void GLCanvas3D::reload_scene(bool refresh_immediately, bool force_full_scene_re
     struct ModelVolumeState {
         ModelVolumeState(const GLVolume *volume) : 
 			model_volume(nullptr), geometry_id(volume->geometry_id), volume_idx(-1) {}
-		ModelVolumeState(const ModelVolume *model_volume, const ModelID &instance_id, const GLVolume::CompositeID &composite_id) :
+		ModelVolumeState(const ModelVolume *model_volume, const ObjectID &instance_id, const GLVolume::CompositeID &composite_id) :
 			model_volume(model_volume), geometry_id(std::make_pair(model_volume->id().id, instance_id.id)), composite_id(composite_id), volume_idx(-1) {}
-		ModelVolumeState(const ModelID &volume_id, const ModelID &instance_id) :
+		ModelVolumeState(const ObjectID &volume_id, const ObjectID &instance_id) :
 			model_volume(nullptr), geometry_id(std::make_pair(volume_id.id, instance_id.id)), volume_idx(-1) {}
 		bool new_geometry() const { return this->volume_idx == size_t(-1); }
 		const ModelVolume		   *model_volume;
-        // ModelID of ModelVolume + ModelID of ModelInstance
-        // or timestamp of an SLAPrintObjectStep + ModelID of ModelInstance
+        // ObjectID of ModelVolume + ObjectID of ModelInstance
+        // or timestamp of an SLAPrintObjectStep + ObjectID of ModelInstance
         std::pair<size_t, size_t>   geometry_id;
         GLVolume::CompositeID       composite_id;
         // Volume index in the new GLVolume vector.
@@ -2316,6 +2318,9 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
         return;
     }
 
+    if ((keyCode == WXK_ESCAPE) && _deactivate_undo_redo_toolbar_items())
+        return;
+
     if (m_gizmos.on_char(evt, *this))
         return;
 
@@ -2348,6 +2353,25 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
 #endif /* __APPLE__ */
             post_event(SimpleEvent(EVT_GLTOOLBAR_PASTE));
         break;
+
+
+#ifdef __APPLE__
+        case 'y':
+        case 'Y':
+#else /* __APPLE__ */
+        case WXK_CONTROL_Y:
+#endif /* __APPLE__ */
+            post_event(SimpleEvent(EVT_GLCANVAS_REDO));
+        break;
+#ifdef __APPLE__
+        case 'z':
+        case 'Z':
+#else /* __APPLE__ */
+        case WXK_CONTROL_Z:
+#endif /* __APPLE__ */
+            post_event(SimpleEvent(EVT_GLCANVAS_UNDO));
+        break;
+
 #ifdef __APPLE__
         case WXK_BACK: // the low cost Apple solutions are not equipped with a Delete key, use Backspace instead.
 #else /* __APPLE__ */
@@ -2368,7 +2392,6 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
 #endif /* __APPLE__ */
                   post_event(SimpleEvent(EVT_GLTOOLBAR_DELETE));
                   break;
-
         case WXK_ESCAPE: { deselect_all(); break; }
         case '0': { select_view("iso"); break; }
         case '1': { select_view("top"); break; }
@@ -2715,12 +2738,17 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
     }
     else if (evt.Leaving())
     {
+        _deactivate_undo_redo_toolbar_items();
+
         // to remove hover on objects when the mouse goes out of this canvas
         m_mouse.position = Vec2d(-1.0, -1.0);
         m_dirty = true;
     }
-    else if (evt.LeftDown() || evt.RightDown())
+    else if (evt.LeftDown() || evt.RightDown() || evt.MiddleDown())
     {
+        if (_deactivate_undo_redo_toolbar_items())
+            return;
+
         // If user pressed left or right button we first check whether this happened
         // on a volume or not.
         m_layers_editing.state = LayersEditing::Unknown;
@@ -2918,9 +2946,9 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
         else if ((m_mouse.drag.move_volume_idx != -1) && m_mouse.dragging)
         {
             m_regenerate_volumes = false;
-            do_move();
+            do_move("Move Object");
             wxGetApp().obj_manipul()->set_dirty();
-            // Let the platter know that the dragging finished, so a delayed refresh
+            // Let the plater know that the dragging finished, so a delayed refresh
             // of the scene with the background processing data should be performed.
             post_event(SimpleEvent(EVT_GLCANVAS_MOUSE_DRAGGING_FINISHED));
         }
@@ -3077,11 +3105,14 @@ void GLCanvas3D::set_tooltip(const std::string& tooltip) const
 }
 
 
-void GLCanvas3D::do_move()
+void GLCanvas3D::do_move(const std::string& snapshot_type)
 {
     if (m_model == nullptr)
         return;
 
+    if (!snapshot_type.empty())
+        wxGetApp().plater()->take_snapshot(_(L(snapshot_type)));
+
     std::set<std::pair<int, int>> done;  // keeps track of modified instances
     bool object_moved = false;
     Vec3d wipe_tower_origin = Vec3d::Zero();
@@ -3132,13 +3163,18 @@ void GLCanvas3D::do_move()
 
     if (wipe_tower_origin != Vec3d::Zero())
         post_event(Vec3dEvent(EVT_GLCANVAS_WIPETOWER_MOVED, std::move(wipe_tower_origin)));
+
+    m_dirty = true;
 }
 
-void GLCanvas3D::do_rotate()
+void GLCanvas3D::do_rotate(const std::string& snapshot_type)
 {
     if (m_model == nullptr)
         return;
 
+    if (!snapshot_type.empty())
+        wxGetApp().plater()->take_snapshot(_(L(snapshot_type)));
+
     std::set<std::pair<int, int>> done;  // keeps track of modified instances
 
     Selection::EMode selection_mode = m_selection.get_mode();
@@ -3187,13 +3223,18 @@ void GLCanvas3D::do_rotate()
 
     if (!done.empty())
         post_event(SimpleEvent(EVT_GLCANVAS_INSTANCE_ROTATED));
+
+    m_dirty = true;
 }
 
-void GLCanvas3D::do_scale()
+void GLCanvas3D::do_scale(const std::string& snapshot_type)
 {
     if (m_model == nullptr)
         return;
 
+    if (!snapshot_type.empty())
+        wxGetApp().plater()->take_snapshot(_(L(snapshot_type)));
+
     std::set<std::pair<int, int>> done;  // keeps track of modified instances
 
     Selection::EMode selection_mode = m_selection.get_mode();
@@ -3239,18 +3280,27 @@ void GLCanvas3D::do_scale()
 
     if (!done.empty())
         post_event(SimpleEvent(EVT_GLCANVAS_INSTANCE_ROTATED));
+
+    m_dirty = true;
 }
 
-void GLCanvas3D::do_flatten()
+void GLCanvas3D::do_flatten(const Vec3d& normal, const std::string& snapshot_type)
 {
-    do_rotate();
+    if (!snapshot_type.empty())
+        wxGetApp().plater()->take_snapshot(_(L(snapshot_type)));
+
+    m_selection.flattening_rotate(normal);
+    do_rotate(""); // avoid taking another snapshot
 }
 
-void GLCanvas3D::do_mirror()
+void GLCanvas3D::do_mirror(const std::string& snapshot_type)
 {
     if (m_model == nullptr)
         return;
 
+    if (!snapshot_type.empty())
+        wxGetApp().plater()->take_snapshot(_(L(snapshot_type)));
+
     std::set<std::pair<int, int>> done;  // keeps track of modified instances
 
     Selection::EMode selection_mode = m_selection.get_mode();
@@ -3289,6 +3339,8 @@ void GLCanvas3D::do_mirror()
     }
 
     post_event(SimpleEvent(EVT_GLCANVAS_SCHEDULE_BACKGROUND_PROCESS));
+
+    m_dirty = true;
 }
 
 void GLCanvas3D::set_camera_zoom(double zoom)
@@ -3412,6 +3464,40 @@ bool GLCanvas3D::_is_shown_on_screen() const
     return (m_canvas != nullptr) ? m_canvas->IsShownOnScreen() : false;
 }
 
+// Getter for the const char*[]
+static bool string_getter(const bool is_undo, int idx, const char** out_text)
+{
+    return wxGetApp().plater()->undo_redo_string_getter(is_undo, idx, out_text);
+}
+
+void GLCanvas3D::_render_undo_redo_stack(const bool is_undo, float pos_x)
+{
+    const wxString& stack_name = _(is_undo ? L("Undo") : L("Redo"));
+    ImGuiWrapper* imgui = wxGetApp().imgui();
+
+    const float x = pos_x * (float)get_camera().get_zoom() + 0.5f * (float)get_canvas_size().get_width();
+    imgui->set_next_window_pos(x, m_toolbar.get_height(), ImGuiCond_Always, 0.5f, 0.0f);
+    imgui->set_next_window_bg_alpha(0.5f);
+    imgui->begin(wxString::Format(_(L("%s Stack")), stack_name),
+                 ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse);
+
+    int hovered = m_imgui_undo_redo_hovered_pos;
+    int selected = -1;
+    const float em = static_cast<float>(wxGetApp().em_unit());
+
+    if (imgui->undo_redo_list(ImVec2(12 * em, 20 * em), is_undo, &string_getter, hovered, selected))
+        m_imgui_undo_redo_hovered_pos = hovered;
+    else
+        m_imgui_undo_redo_hovered_pos = -1;
+
+    if (selected >= 0)
+        is_undo ? wxGetApp().plater()->undo_to(selected) : wxGetApp().plater()->redo_to(selected);
+
+    imgui->text(wxString::Format(_(L("%s %d Action")), stack_name, hovered + 1));
+
+    imgui->end();
+}
+
 bool GLCanvas3D::_init_toolbar()
 {
     if (!m_toolbar.is_enabled())
@@ -3444,7 +3530,7 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "add.svg";
     item.tooltip = _utf8(L("Add...")) + " [" + GUI::shortkey_ctrl_prefix() + "I]";
     item.sprite_id = 0;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_ADD)); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_ADD)); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3452,8 +3538,8 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "remove.svg";
     item.tooltip = _utf8(L("Delete")) + " [Del]";
     item.sprite_id = 1;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_DELETE)); };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_delete(); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_DELETE)); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_delete(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3461,8 +3547,8 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "delete_all.svg";
     item.tooltip = _utf8(L("Delete all")) + " [" + GUI::shortkey_ctrl_prefix() + "Del]";
     item.sprite_id = 2;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_DELETE_ALL)); };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_delete_all(); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_DELETE_ALL)); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_delete_all(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3470,8 +3556,8 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "arrange.svg";
     item.tooltip = _utf8(L("Arrange")) + " [A]";
     item.sprite_id = 3;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_ARRANGE)); };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_arrange(); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_ARRANGE)); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_arrange(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3482,8 +3568,8 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "copy.svg";
     item.tooltip = _utf8(L("Copy")) + " [" + GUI::shortkey_ctrl_prefix() + "C]";
     item.sprite_id = 4;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_COPY)); };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_copy_to_clipboard(); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_COPY)); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_copy_to_clipboard(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3491,8 +3577,8 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "paste.svg";
     item.tooltip = _utf8(L("Paste")) + " [" + GUI::shortkey_ctrl_prefix() + "V]";
     item.sprite_id = 5;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_PASTE)); };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_paste_from_clipboard(); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_PASTE)); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_paste_from_clipboard(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3503,9 +3589,10 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "instance_add.svg";
     item.tooltip = _utf8(L("Add instance")) + " [+]";
     item.sprite_id = 6;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_MORE)); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_MORE)); };
     item.visibility_callback = []()->bool { return wxGetApp().get_mode() != comSimple; };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_increase_instances(); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_increase_instances(); };
+
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3513,9 +3600,9 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "instance_remove.svg";
     item.tooltip = _utf8(L("Remove instance")) + " [-]";
     item.sprite_id = 7;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_FEWER)); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_FEWER)); };
     item.visibility_callback = []()->bool { return wxGetApp().get_mode() != comSimple; };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_decrease_instances(); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_decrease_instances(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3526,9 +3613,9 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "split_objects.svg";
     item.tooltip = _utf8(L("Split to objects"));
     item.sprite_id = 8;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_SPLIT_OBJECTS)); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_SPLIT_OBJECTS)); };
     item.visibility_callback = GLToolbarItem::Default_Visibility_Callback;
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_split_to_objects(); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_split_to_objects(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3536,9 +3623,9 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "split_parts.svg";
     item.tooltip = _utf8(L("Split to parts"));
     item.sprite_id = 9;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_SPLIT_VOLUMES)); };
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_SPLIT_VOLUMES)); };
     item.visibility_callback = []()->bool { return wxGetApp().get_mode() != comSimple; };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_split_to_volumes(); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_split_to_volumes(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -3549,10 +3636,42 @@ bool GLCanvas3D::_init_toolbar()
     item.icon_filename = "layers_white.svg";
     item.tooltip = _utf8(L("Layers editing"));
     item.sprite_id = 10;
-    item.is_toggable = true;
-    item.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_LAYERSEDITING)); };
+    item.left.toggable = true;
+    item.left.action_callback = [this]() { if (m_canvas != nullptr) wxPostEvent(m_canvas, SimpleEvent(EVT_GLTOOLBAR_LAYERSEDITING)); };
     item.visibility_callback = [this]()->bool { return m_process->current_printer_technology() == ptFFF; };
-    item.enabled_state_callback = []()->bool { return wxGetApp().plater()->can_layers_editing(); };
+    item.enabling_callback = []()->bool { return wxGetApp().plater()->can_layers_editing(); };
+    if (!m_toolbar.add_item(item))
+        return false;
+
+    if (!m_toolbar.add_separator())
+        return false;
+
+    item.name = "undo";
+#if ENABLE_SVG_ICONS
+    item.icon_filename = "undo_toolbar.svg";
+#endif // ENABLE_SVG_ICONS
+    item.tooltip = _utf8(L("Undo")) + " [" + GUI::shortkey_ctrl_prefix() + "Z]";
+    item.sprite_id = 11;
+    item.left.toggable = false;
+    item.left.action_callback = [this]() { post_event(SimpleEvent(EVT_GLCANVAS_UNDO)); };
+    item.right.toggable = true;
+    item.right.action_callback = [this]() { m_imgui_undo_redo_hovered_pos = -1; };
+    item.right.render_callback = [this](float left, float right, float, float) { if (m_canvas != nullptr) _render_undo_redo_stack(true, 0.5f * (left + right)); };
+    item.visibility_callback = []()->bool { return true; };
+    item.enabling_callback = [this]()->bool { return wxGetApp().plater()->can_undo(); };
+    if (!m_toolbar.add_item(item))
+        return false;
+
+    item.name = "redo";
+#if ENABLE_SVG_ICONS
+    item.icon_filename = "redo_toolbar.svg";
+#endif // ENABLE_SVG_ICONS
+    item.tooltip = _utf8(L("Redo")) + " [" + GUI::shortkey_ctrl_prefix() + "Y]";
+    item.sprite_id = 12;
+    item.left.action_callback = [this]() { post_event(SimpleEvent(EVT_GLCANVAS_REDO)); };
+    item.right.action_callback = [this]() { m_imgui_undo_redo_hovered_pos = -1; };
+    item.right.render_callback = [this](float left, float right, float, float) { if (m_canvas != nullptr) _render_undo_redo_stack(false, 0.5f * (left + right)); };
+    item.enabling_callback = [this]()->bool { return wxGetApp().plater()->can_redo(); };
     if (!m_toolbar.add_item(item))
         return false;
 
@@ -5551,6 +5670,22 @@ void GLCanvas3D::_update_selection_from_hover()
     m_dirty = true;
 }
 
+bool GLCanvas3D::_deactivate_undo_redo_toolbar_items()
+{
+    if (m_toolbar.is_item_pressed("undo"))
+    {
+        m_toolbar.force_right_action(m_toolbar.get_item_id("undo"), *this);
+        return true;
+    }
+    else if (m_toolbar.is_item_pressed("redo"))
+    {
+        m_toolbar.force_right_action(m_toolbar.get_item_id("redo"), *this);
+        return true;
+    }
+
+    return false;
+}
+
 const Print* GLCanvas3D::fff_print() const
 {
     return (m_process == nullptr) ? nullptr : m_process->fff_print();
diff --git a/src/slic3r/GUI/GLCanvas3D.hpp b/src/slic3r/GUI/GLCanvas3D.hpp
index 2408e0273..f5a53c6a5 100644
--- a/src/slic3r/GUI/GLCanvas3D.hpp
+++ b/src/slic3r/GUI/GLCanvas3D.hpp
@@ -127,6 +127,8 @@ wxDECLARE_EVENT(EVT_GLCANVAS_TAB, SimpleEvent);
 wxDECLARE_EVENT(EVT_GLCANVAS_RESETGIZMOS, SimpleEvent);
 wxDECLARE_EVENT(EVT_GLCANVAS_MOVE_DOUBLE_SLIDER, wxKeyEvent);
 wxDECLARE_EVENT(EVT_GLCANVAS_EDIT_COLOR_CHANGE, wxKeyEvent);
+wxDECLARE_EVENT(EVT_GLCANVAS_UNDO, SimpleEvent);
+wxDECLARE_EVENT(EVT_GLCANVAS_REDO, SimpleEvent);
 
 class GLCanvas3D
 {
@@ -485,6 +487,8 @@ private:
     RenderStats m_render_stats;
 #endif // ENABLE_RENDER_STATISTICS
 
+    int m_imgui_undo_redo_hovered_pos{ -1 };
+
 public:
     GLCanvas3D(wxGLCanvas* canvas, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar);
     ~GLCanvas3D();
@@ -596,11 +600,12 @@ public:
 
     void set_tooltip(const std::string& tooltip) const;
 
-    void do_move();
-    void do_rotate();
-    void do_scale();
-    void do_flatten();
-    void do_mirror();
+    // the following methods add a snapshot to the undo/redo stack, unless the given string is empty
+    void do_move(const std::string& snapshot_type);
+    void do_rotate(const std::string& snapshot_type);
+    void do_scale(const std::string& snapshot_type);
+    void do_flatten(const Vec3d& normal, const std::string& snapshot_type);
+    void do_mirror(const std::string& snapshot_type);
 
     void set_camera_zoom(double zoom);
 
@@ -673,6 +678,7 @@ private:
 #endif // ENABLE_SHOW_CAMERA_TARGET
     void _render_sla_slices() const;
     void _render_selection_sidebar_hints() const;
+    void _render_undo_redo_stack(const bool is_undo, float pos_x);
 
     void _update_volumes_hover_state() const;
 
@@ -731,6 +737,8 @@ private:
     // updates the selection from the content of m_hover_volume_idxs
     void _update_selection_from_hover();
 
+    bool _deactivate_undo_redo_toolbar_items();
+
     static std::vector<float> _parse_colors(const std::vector<std::string>& colors);
 
 public:
diff --git a/src/slic3r/GUI/GLToolbar.cpp b/src/slic3r/GUI/GLToolbar.cpp
index 97bb957ea..0002eda2d 100644
--- a/src/slic3r/GUI/GLToolbar.cpp
+++ b/src/slic3r/GUI/GLToolbar.cpp
@@ -34,18 +34,24 @@ wxDEFINE_EVENT(EVT_GLVIEWTOOLBAR_PREVIEW, SimpleEvent);
 
 const GLToolbarItem::ActionCallback GLToolbarItem::Default_Action_Callback = [](){};
 const GLToolbarItem::VisibilityCallback GLToolbarItem::Default_Visibility_Callback = []()->bool { return true; };
-const GLToolbarItem::EnabledStateCallback GLToolbarItem::Default_Enabled_State_Callback = []()->bool { return true; };
+const GLToolbarItem::EnablingCallback GLToolbarItem::Default_Enabling_Callback = []()->bool { return true; };
+const GLToolbarItem::RenderCallback GLToolbarItem::Default_Render_Callback = [](float, float, float, float){};
+
+GLToolbarItem::Data::Option::Option()
+    : toggable(false)
+    , action_callback(Default_Action_Callback)
+    , render_callback(nullptr)
+{
+}
 
 GLToolbarItem::Data::Data()
     : name("")
     , icon_filename("")
     , tooltip("")
     , sprite_id(-1)
-    , is_toggable(false)
     , visible(true)
-    , action_callback(Default_Action_Callback)
     , visibility_callback(Default_Visibility_Callback)
-    , enabled_state_callback(Default_Enabled_State_Callback)
+    , enabling_callback(Default_Enabling_Callback)
 {
 }
 
@@ -53,6 +59,7 @@ GLToolbarItem::GLToolbarItem(GLToolbarItem::EType type, const GLToolbarItem::Dat
     : m_type(type)
     , m_state(Normal)
     , m_data(data)
+    , m_last_action_type(Undefined)
 {
 }
 
@@ -68,7 +75,7 @@ bool GLToolbarItem::update_visibility()
 
 bool GLToolbarItem::update_enabled_state()
 {
-    bool enabled = m_data.enabled_state_callback();
+    bool enabled = m_data.enabling_callback();
     bool ret = (is_enabled() != enabled);
     if (ret)
         m_state = enabled ? GLToolbarItem::Normal : GLToolbarItem::Disabled;
@@ -79,6 +86,14 @@ bool GLToolbarItem::update_enabled_state()
 void GLToolbarItem::render(unsigned int tex_id, float left, float right, float bottom, float top, unsigned int tex_width, unsigned int tex_height, unsigned int icon_size) const
 {
     GLTexture::render_sub_texture(tex_id, left, right, bottom, top, get_uvs(tex_width, tex_height, icon_size));
+
+    if (is_pressed())
+    {
+        if ((m_last_action_type == Left) && m_data.left.can_render())
+            m_data.left.render_callback(left, right, bottom, top);
+        else if ((m_last_action_type == Right) && m_data.right.can_render())
+            m_data.right.render_callback(left, right, bottom, top);
+    }
 }
 
 GLTexture::Quad_UVs GLToolbarItem::get_uvs(unsigned int tex_width, unsigned int tex_height, unsigned int icon_size) const
@@ -136,6 +151,7 @@ GLToolbar::GLToolbar(GLToolbar::EType type, const std::string& name)
     , m_enabled(false)
     , m_icons_texture_dirty(true)
     , m_tooltip("")
+    , m_pressed_toggable_id(-1)
 {
 }
 
@@ -295,7 +311,7 @@ void GLToolbar::select_item(const std::string& name)
 
 bool GLToolbar::is_item_pressed(const std::string& name) const
 {
-    for (GLToolbarItem* item : m_items)
+    for (const GLToolbarItem* item : m_items)
     {
         if (item->get_name() == name)
             return item->is_pressed();
@@ -306,7 +322,7 @@ bool GLToolbar::is_item_pressed(const std::string& name) const
 
 bool GLToolbar::is_item_disabled(const std::string& name) const
 {
-    for (GLToolbarItem* item : m_items)
+    for (const GLToolbarItem* item : m_items)
     {
         if (item->get_name() == name)
             return item->is_disabled();
@@ -317,7 +333,7 @@ bool GLToolbar::is_item_disabled(const std::string& name) const
 
 bool GLToolbar::is_item_visible(const std::string& name) const
 {
-    for (GLToolbarItem* item : m_items)
+    for (const GLToolbarItem* item : m_items)
     {
         if (item->get_name() == name)
             return item->is_visible();
@@ -326,11 +342,46 @@ bool GLToolbar::is_item_visible(const std::string& name) const
     return false;
 }
 
+bool GLToolbar::is_any_item_pressed() const
+{
+    for (const GLToolbarItem* item : m_items)
+    {
+        if (item->is_pressed())
+            return true;
+    }
+
+    return false;
+}
+
+unsigned int GLToolbar::get_item_id(const std::string& name) const
+{
+    for (unsigned int i = 0; i < (unsigned int)m_items.size(); ++i)
+    {
+        if (m_items[i]->get_name() == name)
+            return i;
+    }
+
+    return -1;
+}
+
+void GLToolbar::force_left_action(unsigned int item_id, GLCanvas3D& parent)
+{
+    do_action(GLToolbarItem::Left, item_id, parent, false);
+}
+
+void GLToolbar::force_right_action(unsigned int item_id, GLCanvas3D& parent)
+{
+    do_action(GLToolbarItem::Right, item_id, parent, false);
+}
+
 bool GLToolbar::update_items_state()
 {
     bool ret = false;
     ret |= update_items_visibility();
     ret |= update_items_enabled_state();
+    if (!is_any_item_pressed())
+        m_pressed_toggable_id = -1;
+
     return ret;
 }
 
@@ -392,10 +443,11 @@ bool GLToolbar::on_mouse(wxMouseEvent& evt, GLCanvas3D& parent)
             m_mouse_capture.left = true;
             m_mouse_capture.parent = &parent;
             processed = true;
-            if ((item_id != -2) && !m_items[item_id]->is_separator())
+            if ((item_id != -2) && !m_items[item_id]->is_separator() && ((m_pressed_toggable_id == -1) || (m_items[item_id]->get_last_action_type() == GLToolbarItem::Left)))
             {
                 // mouse is inside an icon
-                do_action((unsigned int)item_id, parent);
+                do_action(GLToolbarItem::Left, (unsigned int)item_id, parent, true);
+                parent.set_as_dirty();
             }
         }
         else if (evt.MiddleDown())
@@ -407,6 +459,13 @@ bool GLToolbar::on_mouse(wxMouseEvent& evt, GLCanvas3D& parent)
         {
             m_mouse_capture.right = true;
             m_mouse_capture.parent = &parent;
+            processed = true;
+            if ((item_id != -2) && !m_items[item_id]->is_separator() && ((m_pressed_toggable_id == -1) || (m_items[item_id]->get_last_action_type() == GLToolbarItem::Right)))
+            {
+                // mouse is inside an icon
+                do_action(GLToolbarItem::Right, (unsigned int)item_id, parent, true);
+                parent.set_as_dirty();
+            }
         }
         else if (evt.LeftUp())
             processed = true;
@@ -477,38 +536,61 @@ float GLToolbar::get_main_size() const
     return size * m_layout.scale;
 }
 
-void GLToolbar::do_action(unsigned int item_id, GLCanvas3D& parent)
+void GLToolbar::do_action(GLToolbarItem::EActionType type, unsigned int item_id, GLCanvas3D& parent, bool check_hover)
 {
-    if (item_id < (unsigned int)m_items.size())
+    if ((m_pressed_toggable_id == -1) || (m_pressed_toggable_id == item_id))
     {
-        GLToolbarItem* item = m_items[item_id];
-        if ((item != nullptr) && !item->is_separator() && item->is_hovered())
+        if (item_id < (unsigned int)m_items.size())
         {
-            if (item->is_toggable())
+            GLToolbarItem* item = m_items[item_id];
+            if ((item != nullptr) && !item->is_separator() && (!check_hover || item->is_hovered()))
             {
-                GLToolbarItem::EState state = item->get_state();
-                if (state == GLToolbarItem::Hover)
-                    item->set_state(GLToolbarItem::HoverPressed);
-                else if (state == GLToolbarItem::HoverPressed)
-                    item->set_state(GLToolbarItem::Hover);
+                if (((type == GLToolbarItem::Right) && item->is_right_toggable()) ||
+                    ((type == GLToolbarItem::Left) && item->is_left_toggable()))
+                {
+                    GLToolbarItem::EState state = item->get_state();
+                    if (state == GLToolbarItem::Hover)
+                        item->set_state(GLToolbarItem::HoverPressed);
+                    else if (state == GLToolbarItem::HoverPressed)
+                        item->set_state(GLToolbarItem::Hover);
+                    else if (state == GLToolbarItem::Pressed)
+                        item->set_state(GLToolbarItem::Normal);
+                    else if (state == GLToolbarItem::Normal)
+                        item->set_state(GLToolbarItem::Pressed);
+
+                    m_pressed_toggable_id = item->is_pressed() ? item_id : -1;
+                    item->reset_last_action_type();
 
-                parent.render();
-                item->do_action();
-            }
-            else
-            {
-                if (m_type == Radio)
-                    select_item(item->get_name());
+                    parent.render();
+                    switch (type)
+                    {
+                    default:
+                    case GLToolbarItem::Left: { item->do_left_action(); break; }
+                    case GLToolbarItem::Right: { item->do_right_action(); break; }
+                    }
+                }
                 else
-                    item->set_state(GLToolbarItem::HoverPressed);
-
-                parent.render();
-                item->do_action();
-                if ((m_type == Normal) && (item->get_state() != GLToolbarItem::Disabled))
                 {
-                    // the item may get disabled during the action, if not, set it back to hover state
-                    item->set_state(GLToolbarItem::Hover);
+                    if (m_type == Radio)
+                        select_item(item->get_name());
+                    else
+                        item->set_state(item->is_hovered() ? GLToolbarItem::HoverPressed : GLToolbarItem::Pressed);
+
+                    item->reset_last_action_type();
                     parent.render();
+                    switch (type)
+                    {
+                    default:
+                    case GLToolbarItem::Left: { item->do_left_action(); break; }
+                    case GLToolbarItem::Right: { item->do_right_action(); break; }
+                    }
+
+                    if ((m_type == Normal) && (item->get_state() != GLToolbarItem::Disabled))
+                    {
+                        // the item may get disabled during the action, if not, set it back to hover state
+                        item->set_state(GLToolbarItem::Hover);
+                        parent.render();
+                    }
                 }
             }
         }
@@ -1212,9 +1294,15 @@ bool GLToolbar::update_items_enabled_state()
 {
     bool ret = false;
 
-    for (GLToolbarItem* item : m_items)
+    for (unsigned int i = 0; i < (unsigned int)m_items.size(); ++i)
     {
+        GLToolbarItem* item = m_items[i];
         ret |= item->update_enabled_state();
+        if (item->is_enabled() && (m_pressed_toggable_id != -1) && (m_pressed_toggable_id != i))
+        {
+            ret = true;
+            item->set_state(GLToolbarItem::Disabled);
+        }
     }
 
     if (ret)
diff --git a/src/slic3r/GUI/GLToolbar.hpp b/src/slic3r/GUI/GLToolbar.hpp
index 7b4cf8b10..875b2f9f6 100644
--- a/src/slic3r/GUI/GLToolbar.hpp
+++ b/src/slic3r/GUI/GLToolbar.hpp
@@ -36,7 +36,8 @@ class GLToolbarItem
 public:
     typedef std::function<void()> ActionCallback;
     typedef std::function<bool()> VisibilityCallback;
-    typedef std::function<bool()> EnabledStateCallback;
+    typedef std::function<bool()> EnablingCallback;
+    typedef std::function<void(float, float, float, float)> RenderCallback;
 
     enum EType : unsigned char
     {
@@ -45,6 +46,14 @@ public:
         Num_Types
     };
 
+    enum EActionType : unsigned char
+    {
+        Undefined,
+        Left,
+        Right,
+        Num_Action_Types
+    };
+
     enum EState : unsigned char
     {
         Normal,
@@ -57,27 +66,42 @@ public:
 
     struct Data
     {
+        struct Option
+        {
+            bool toggable;
+            ActionCallback action_callback;
+            RenderCallback render_callback;
+
+            Option();
+
+            bool can_render() const { return toggable && (render_callback != nullptr); }
+        };
+
         std::string name;
         std::string icon_filename;
         std::string tooltip;
         unsigned int sprite_id;
-        bool is_toggable;
+        // mouse left click
+        Option left;
+        // mouse right click
+        Option right;
         bool visible;
-        ActionCallback action_callback;
         VisibilityCallback visibility_callback;
-        EnabledStateCallback enabled_state_callback;
+        EnablingCallback enabling_callback;
 
         Data();
     };
 
     static const ActionCallback Default_Action_Callback;
     static const VisibilityCallback Default_Visibility_Callback;
-    static const EnabledStateCallback Default_Enabled_State_Callback;
+    static const EnablingCallback Default_Enabling_Callback;
+    static const RenderCallback Default_Render_Callback;
 
 private:
     EType m_type;
     EState m_state;
     Data m_data;
+    EActionType m_last_action_type;
 
 public:
     GLToolbarItem(EType type, const Data& data);
@@ -89,17 +113,25 @@ public:
     const std::string& get_icon_filename() const { return m_data.icon_filename; }
     const std::string& get_tooltip() const { return m_data.tooltip; }
 
-    void do_action() { m_data.action_callback(); }
+    void do_left_action() { m_last_action_type = Left; m_data.left.action_callback(); }
+    void do_right_action() { m_last_action_type = Right; m_data.right.action_callback(); }
 
     bool is_enabled() const { return m_state != Disabled; }
     bool is_disabled() const { return m_state == Disabled; }
     bool is_hovered() const { return (m_state == Hover) || (m_state == HoverPressed); }
     bool is_pressed() const { return (m_state == Pressed) || (m_state == HoverPressed); }
-
-    bool is_toggable() const { return m_data.is_toggable; }
     bool is_visible() const { return m_data.visible; }
     bool is_separator() const { return m_type == Separator; }
 
+    bool is_left_toggable() const { return m_data.left.toggable; }
+    bool is_right_toggable() const { return m_data.right.toggable; }
+
+    bool has_left_render_callback() const { return m_data.left.render_callback != nullptr; }
+    bool has_right_render_callback() const { return m_data.right.render_callback != nullptr; }
+
+    EActionType get_last_action_type() const { return m_last_action_type; }
+    void reset_last_action_type() { m_last_action_type = Undefined; }
+
     // returns true if the state changes
     bool update_visibility();
     // returns true if the state changes
@@ -212,6 +244,7 @@ private:
 
     MouseCapture m_mouse_capture;
     std::string m_tooltip;
+    unsigned int m_pressed_toggable_id;
 
 public:
     GLToolbar(EType type, const std::string& name);
@@ -246,6 +279,13 @@ public:
     bool is_item_disabled(const std::string& name) const;
     bool is_item_visible(const std::string& name) const;
 
+    bool is_any_item_pressed() const;
+
+    unsigned int get_item_id(const std::string& name) const;
+
+    void force_left_action(unsigned int item_id, GLCanvas3D& parent);
+    void force_right_action(unsigned int item_id, GLCanvas3D& parent);
+
     const std::string& get_tooltip() const { return m_tooltip; }
 
     // returns true if any item changed its state
@@ -262,7 +302,7 @@ private:
     float get_height_horizontal() const;
     float get_height_vertical() const;
     float get_main_size() const;
-    void do_action(unsigned int item_id, GLCanvas3D& parent);
+    void do_action(GLToolbarItem::EActionType type, unsigned int item_id, GLCanvas3D& parent, bool check_hover);
     std::string update_hover_state(const Vec2d& mouse_pos, GLCanvas3D& parent);
     std::string update_hover_state_horizontal(const Vec2d& mouse_pos, GLCanvas3D& parent);
     std::string update_hover_state_vertical(const Vec2d& mouse_pos, GLCanvas3D& parent);
diff --git a/src/slic3r/GUI/GUI_ObjectList.cpp b/src/slic3r/GUI/GUI_ObjectList.cpp
index 4c4a30227..9e681257c 100644
--- a/src/slic3r/GUI/GUI_ObjectList.cpp
+++ b/src/slic3r/GUI/GUI_ObjectList.cpp
@@ -25,7 +25,7 @@ namespace GUI
 wxDEFINE_EVENT(EVT_OBJ_LIST_OBJECT_SELECT, SimpleEvent);
 
 // pt_FFF
-FreqSettingsBundle FREQ_SETTINGS_BUNDLE_FFF =
+SettingsBundle FREQ_SETTINGS_BUNDLE_FFF =
 {
     { L("Layers and Perimeters"), { "layer_height" , "perimeters", "top_solid_layers", "bottom_solid_layers" } },
     { L("Infill")               , { "fill_density", "fill_pattern" } },
@@ -36,7 +36,7 @@ FreqSettingsBundle FREQ_SETTINGS_BUNDLE_FFF =
 };
 
 // pt_SLA
-FreqSettingsBundle FREQ_SETTINGS_BUNDLE_SLA =
+SettingsBundle FREQ_SETTINGS_BUNDLE_SLA =
 {
     { L("Pad and Support")      , { "supports_enable", "pad_enable" } }
 };
@@ -66,6 +66,14 @@ static int extruders_count()
     return wxGetApp().extruders_cnt();
 }
 
+static void take_snapshot(const wxString& snapshot_name) 
+{
+    wxGetApp().plater()->take_snapshot(snapshot_name);
+}
+
+static void suppress_snapshots(){ wxGetApp().plater()->suppress_snapshots(); }
+static void allow_snapshots()   { wxGetApp().plater()->allow_snapshots(); }
+
 ObjectList::ObjectList(wxWindow* parent) :
     wxDataViewCtrl(parent, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxDV_MULTIPLE),
     m_parent(parent)
@@ -138,20 +146,24 @@ ObjectList::ObjectList(wxWindow* parent) :
 //    Bind(wxEVT_KEY_DOWN, &ObjectList::OnChar, this);
     {
         // Accelerators
-        wxAcceleratorEntry entries[6];
+        wxAcceleratorEntry entries[8];
         entries[0].Set(wxACCEL_CTRL, (int) 'C',    wxID_COPY);
         entries[1].Set(wxACCEL_CTRL, (int) 'X',    wxID_CUT);
         entries[2].Set(wxACCEL_CTRL, (int) 'V',    wxID_PASTE);
         entries[3].Set(wxACCEL_CTRL, (int) 'A',    wxID_SELECTALL);
-        entries[4].Set(wxACCEL_NORMAL, WXK_DELETE, wxID_DELETE);
-        entries[5].Set(wxACCEL_NORMAL, WXK_BACK,   wxID_DELETE);
-        wxAcceleratorTable accel(6, entries);
+        entries[4].Set(wxACCEL_CTRL, (int) 'Z',    wxID_UNDO);
+        entries[5].Set(wxACCEL_CTRL, (int) 'Y',    wxID_REDO);
+        entries[6].Set(wxACCEL_NORMAL, WXK_DELETE, wxID_DELETE);
+        entries[7].Set(wxACCEL_NORMAL, WXK_BACK,   wxID_DELETE);
+        wxAcceleratorTable accel(8, entries);
         SetAcceleratorTable(accel);
 
         this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->copy();                      }, wxID_COPY);
         this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->paste();                     }, wxID_PASTE);
         this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->select_item_all_children();  }, wxID_SELECTALL);
         this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->remove();                    }, wxID_DELETE);
+        this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->undo();  					}, wxID_UNDO);
+        this->Bind(wxEVT_MENU, [this](wxCommandEvent &evt) { this->redo();                    	}, wxID_REDO);
     }
 #else __WXOSX__
     Bind(wxEVT_CHAR, [this](wxKeyEvent& event) { key_event(event); }); // doesn't work on OSX
@@ -655,7 +667,6 @@ void ObjectList::paste_volumes_into_list(int obj_idx, const ModelVolumePtrs& vol
     if (volumes.empty())
         return;
 
-    ModelObject& model_object = *(*m_objects)[obj_idx];
     const auto object_item = m_objects_model->GetItemById(obj_idx);
 
     wxDataViewItemArray items;
@@ -665,10 +676,7 @@ void ObjectList::paste_volumes_into_list(int obj_idx, const ModelVolumePtrs& vol
         const wxDataViewItem& vol_item = m_objects_model->AddVolumeChild(object_item, wxString::FromUTF8(volume->name.c_str()), volume->type(), 
             volume->get_mesh_errors_count()>0 ,
             volume->config.has("extruder") ? volume->config.option<ConfigOptionInt>("extruder")->value : 0);
-        auto opt_keys = volume->config.keys();
-        if (!opt_keys.empty() && !((opt_keys.size() == 1) && (opt_keys[0] == "extruder")))
-            select_item(m_objects_model->AddSettingsChild(vol_item));
-
+        add_settings_item(vol_item, &volume->config);
         items.Add(vol_item);
     }
 
@@ -805,6 +813,16 @@ void ObjectList::paste()
         wxPostEvent((wxEvtHandler*)wxGetApp().plater()->canvas3D()->get_wxglcanvas(), SimpleEvent(EVT_GLTOOLBAR_PASTE));
 }
 
+void ObjectList::undo()
+{
+	wxGetApp().plater()->undo();
+}
+
+void ObjectList::redo()
+{
+	wxGetApp().plater()->redo();	
+}
+
 #ifndef __WXOSX__
 void ObjectList::key_event(wxKeyEvent& event)
 {
@@ -823,6 +841,10 @@ void ObjectList::key_event(wxKeyEvent& event)
         copy();
     else if (wxGetKeyState(wxKeyCode('V')) && wxGetKeyState(WXK_CONTROL))
         paste();
+    else if (wxGetKeyState(wxKeyCode('Y')) && wxGetKeyState(WXK_CONTROL))
+        redo();
+    else if (wxGetKeyState(wxKeyCode('Z')) && wxGetKeyState(WXK_CONTROL))
+        undo();
     else
         event.Skip();
 }
@@ -908,6 +930,7 @@ void ObjectList::OnDrop(wxDataViewEvent &event)
 
     if (m_dragged_data.type() == itInstance)
     {
+        take_snapshot(_(L("Instances to Separated Objects")));
         instances_to_separated_object(m_dragged_data.obj_idx(), m_dragged_data.inst_idxs());
         m_dragged_data.clear();
         return;
@@ -925,6 +948,8 @@ void ObjectList::OnDrop(wxDataViewEvent &event)
 //     if (to_volume_id > from_volume_id) to_volume_id--;
 // #endif // __WXGTK__
 
+    take_snapshot(_(L("Remov Volume(s)")));
+
     auto& volumes = (*m_objects)[m_dragged_data.obj_idx()]->volumes;
     auto delta = to_volume_id < from_volume_id ? -1 : 1;
     int cnt = 0;
@@ -963,7 +988,7 @@ std::vector<std::string> ObjectList::get_options(const bool is_part)
     
 const std::vector<std::string>& ObjectList::get_options_for_bundle(const wxString& bundle_name)
 {
-    const FreqSettingsBundle& bundle = printer_technology() == ptSLA ? 
+    const SettingsBundle& bundle = printer_technology() == ptSLA ? 
                                        FREQ_SETTINGS_BUNDLE_SLA : FREQ_SETTINGS_BUNDLE_FFF;
 
     for (auto& it : bundle)
@@ -973,7 +998,7 @@ const std::vector<std::string>& ObjectList::get_options_for_bundle(const wxStrin
     }
 #if 0
     // if "Quick menu" is selected
-    FreqSettingsBundle& bundle_quick = printer_technology() == ptSLA ?
+    SettingsBundle& bundle_quick = printer_technology() == ptSLA ?
                                        m_freq_settings_sla: m_freq_settings_fff;
 
     for (auto& it : bundle_quick)
@@ -1049,7 +1074,7 @@ void ObjectList::get_settings_choice(const wxString& category_name)
     if (selection_cnt > 0) 
     {
         // Add selected items to the "Quick menu"
-        FreqSettingsBundle& freq_settings = printer_technology() == ptSLA ?
+        SettingsBundle& freq_settings = printer_technology() == ptSLA ?
                                             m_freq_settings_sla : m_freq_settings_fff;
         bool changed_existing = false;
 
@@ -1090,6 +1115,8 @@ void ObjectList::get_settings_choice(const wxString& category_name)
     }
 #endif
 
+    take_snapshot(wxString::Format(_(L("Add Settings for %s")), is_part ? _(L("Sub-object")) : _(L("Object"))));
+
     std::vector <std::string> selected_options;
     selected_options.reserve(selection_cnt);
     for (auto sel : selections)
@@ -1119,8 +1146,8 @@ void ObjectList::get_settings_choice(const wxString& category_name)
     }
 
 
-    // Add settings item for object
-    update_settings_item();
+    // Add settings item for object/sub-object and show them 
+    show_settings(add_settings_item(GetSelection(), m_config));    
 }
 
 void ObjectList::get_freq_settings_choice(const wxString& bundle_name)
@@ -1140,6 +1167,8 @@ void ObjectList::get_freq_settings_choice(const wxString& bundle_name)
     assert(m_config);
     auto opt_keys = m_config->keys();
 
+    take_snapshot(wxString::Format(_(L("Add Settings Bundle for %s")), m_objects_model->GetItemType(GetSelection()) & itObject ? _(L("Object")) : _(L("Sub-object"))));
+
     const DynamicPrintConfig& from_config = wxGetApp().preset_bundle->prints.get_edited_preset().config;
     for (auto& opt_key : options)
     {
@@ -1154,13 +1183,21 @@ void ObjectList::get_freq_settings_choice(const wxString& bundle_name)
         }
     }
 
-    // Add settings item for object
-    update_settings_item();
+    // Add settings item for object/sub-object and show them 
+    show_settings(add_settings_item(GetSelection(), m_config));
 }
 
-void ObjectList::update_settings_item()
+void ObjectList::show_settings(const wxDataViewItem settings_item)
 {
-    auto item = GetSelection();
+    if (!settings_item)
+        return;
+
+    select_item(settings_item);
+    
+    // update object selection on Plater
+    if (!m_prevent_canvas_selection_update)
+        update_selections_on_canvas();
+/*    auto item = GetSelection();
     if (item) {
         if (m_objects_model->GetItemType(item) == itInstance)
             item = m_objects_model->GetTopParent(item);
@@ -1172,12 +1209,14 @@ void ObjectList::update_settings_item()
         if (!m_prevent_canvas_selection_update)
             update_selections_on_canvas();
     }
-    else {
+    else { 
+        //# ys_FIXME ??? use case ???
         auto panel = wxGetApp().sidebar().scrolled_panel();
         panel->Freeze();
         wxGetApp().obj_settings()->UpdateAndShow(true);
         panel->Thaw();
     }
+    */
 }
 
 wxMenu* ObjectList::append_submenu_add_generic(wxMenu* menu, const ModelVolumeType type) {
@@ -1488,7 +1527,7 @@ wxMenu* ObjectList::create_settings_popupmenu(wxMenu *parent_menu)
 void ObjectList::create_freq_settings_popupmenu(wxMenu *menu)
 {
     // Add default settings bundles
-    const FreqSettingsBundle& bundle = printer_technology() == ptFFF ?
+    const SettingsBundle& bundle = printer_technology() == ptFFF ?
                                      FREQ_SETTINGS_BUNDLE_FFF : FREQ_SETTINGS_BUNDLE_SLA;
 
     const int extruders_cnt = extruders_count();
@@ -1503,7 +1542,7 @@ void ObjectList::create_freq_settings_popupmenu(wxMenu *menu)
     }
 #if 0
     // Add "Quick" settings bundles
-    const FreqSettingsBundle& bundle_quick = printer_technology() == ptFFF ?
+    const SettingsBundle& bundle_quick = printer_technology() == ptFFF ?
                                              m_freq_settings_fff : m_freq_settings_sla;
 
     for (auto& it : bundle_quick) {
@@ -1539,6 +1578,8 @@ void ObjectList::load_subobject(ModelVolumeType type)
     if (m_objects_model->GetItemType(item)&itInstance)
         item = m_objects_model->GetItemById(obj_idx);
 
+    take_snapshot(_(L("Load Part")));
+
     std::vector<std::pair<wxString, bool>> volumes_info;
     load_part((*m_objects)[obj_idx], volumes_info, type);
 
@@ -1614,6 +1655,8 @@ void ObjectList::load_generic_subobject(const std::string& type_name, const Mode
     if (instance_idx == -1)
         return;
 
+    take_snapshot(_(L("Add Generic Subobject")));
+
     // Selected object
     ModelObject  &model_object = *(*m_objects)[obj_idx];
     // Bounding box of the selected instance in world coordinate system including the translation, without modifiers.
@@ -1720,6 +1763,8 @@ void ObjectList::del_settings_from_config(const wxDataViewItem& parent_item)
         is_layer_settings && opt_cnt == 2 && m_config->has("extruder") && m_config->has("layer_height"))
         return;
 
+    take_snapshot(_(L("Delete Settings")));
+
     int extruder = -1;
     if (m_config->has("extruder"))
         extruder = m_config->option<ConfigOptionInt>("extruder")->value;
@@ -1742,6 +1787,8 @@ void ObjectList::del_instances_from_object(const int obj_idx)
     if (instances.size() <= 1)
         return;
 
+    take_snapshot(_(L("Delete All Instances from Object")));
+
     while ( instances.size()> 1)
         instances.pop_back();
 
@@ -1755,6 +1802,8 @@ void ObjectList::del_layer_from_object(const int obj_idx, const t_layer_height_r
     const auto del_range = object(obj_idx)->layer_config_ranges.find(layer_range);
     if (del_range == object(obj_idx)->layer_config_ranges.end())
         return;
+
+    take_snapshot(_(L("Delete Layers Range")));
         
     object(obj_idx)->layer_config_ranges.erase(del_range);
 
@@ -1789,6 +1838,8 @@ bool ObjectList::del_subobject_from_object(const int obj_idx, const int idx, con
             return false;
         }
 
+        take_snapshot(_(L("Delete Subobject")));
+
         object->delete_volume(idx);
 
         if (object->volumes.size() == 1)
@@ -1805,6 +1856,8 @@ bool ObjectList::del_subobject_from_object(const int obj_idx, const int idx, con
             Slic3r::GUI::show_error(nullptr, _(L("You can't delete the last intance from object.")));
             return false;
         }
+
+        take_snapshot(_(L("Delete Instance")));
         object->delete_instance(idx);
     }
     else
@@ -1832,6 +1885,8 @@ void ObjectList::split()
         return;
     }
 
+    take_snapshot(_(L("Split to Parts")));
+
     wxBusyCursor wait;
 
     auto model_object = (*m_objects)[obj_idx];
@@ -1850,11 +1905,7 @@ void ObjectList::split()
             volume->config.option<ConfigOptionInt>("extruder")->value : 0,
             false);
         // add settings to the part, if it has those
-        auto opt_keys = volume->config.keys();
-        if ( !(opt_keys.size() == 1 && opt_keys[0] == "extruder") ) {
-            select_item(m_objects_model->AddSettingsChild(vol_item));
-            Expand(vol_item);
-        }
+        add_settings_item(vol_item, &volume->config);
     }
 
     if (parent == item)
@@ -1879,8 +1930,10 @@ void ObjectList::layers_editing()
         t_layer_config_ranges& ranges = object(obj_idx)->layer_config_ranges;
 
         // set some default value
-        if (ranges.empty())
+        if (ranges.empty()) {
+            take_snapshot(_(L("Add Layers")));
             ranges[{ 0.0f, 2.0f }] = get_default_layer_config(obj_idx);
+        }
 
         // create layer root item
         layers_item = add_layer_root_item(obj_item);
@@ -1912,6 +1965,7 @@ wxDataViewItem ObjectList::add_layer_root_item(const wxDataViewItem obj_item)
     for (const auto range : object(obj_idx)->layer_config_ranges)
         add_layer_item(range.first, layers_item);
 
+    Expand(layers_item);
     return layers_item;
 }
 
@@ -2097,7 +2151,79 @@ void ObjectList::part_selection_changed()
     panel.Thaw();
 }
 
-void ObjectList::add_object_to_list(size_t obj_idx)
+SettingsBundle ObjectList::get_item_settings_bundle(const DynamicPrintConfig* config, const bool is_layers_range_settings)
+{
+    auto opt_keys = config->keys();
+    if (opt_keys.empty())
+        return SettingsBundle();
+
+    update_opt_keys(opt_keys); // update options list according to print technology
+
+    if (opt_keys.size() == 1 && opt_keys[0] == "extruder" ||
+        is_layers_range_settings && opt_keys.size() == 2)
+        return SettingsBundle();
+
+    const int extruders_cnt = wxGetApp().extruders_edited_cnt();
+
+    SettingsBundle bundle;
+    for (auto& opt_key : opt_keys)
+    {
+        auto category = config->def()->get(opt_key)->category;
+        if (category.empty() || (category == "Extruders" && extruders_cnt == 1)) 
+            continue;
+
+        std::vector< std::string > new_category;
+
+        auto& cat_opt = bundle.find(category) == bundle.end() ? new_category : bundle.at(category);
+        cat_opt.push_back(opt_key);
+        if (cat_opt.size() == 1)
+            bundle[category] = cat_opt;
+    }
+
+    return bundle;
+}
+
+// Add new SettingsItem for parent_item if it doesn't exist, or just update a digest according to new config
+wxDataViewItem ObjectList::add_settings_item(wxDataViewItem parent_item, const DynamicPrintConfig* config)
+{
+    wxDataViewItem ret = wxDataViewItem(0);
+
+    if (!parent_item)
+        return ret;
+
+    const bool is_layers_range_settings = m_objects_model->GetItemType(parent_item) == itLayer;
+    SettingsBundle cat_options = get_item_settings_bundle(config, is_layers_range_settings);
+    if (cat_options.empty())
+        return ret;
+
+    std::vector<std::string> categories;
+    categories.reserve(cat_options.size());
+    for (auto& cat : cat_options)
+    {
+        if (cat.second.size() == 1 &&
+            (cat.second[0] == "extruder" || is_layers_range_settings && cat.second[0] == "layer_height"))
+            continue;
+
+        categories.push_back(cat.first);
+    }
+
+    if (categories.empty())
+        return ret;
+
+    if (m_objects_model->GetItemType(parent_item) & itInstance)
+        parent_item = m_objects_model->GetTopParent(parent_item);
+
+    ret = m_objects_model->IsSettingsItem(parent_item) ? parent_item : m_objects_model->GetSettingsItem(parent_item);
+
+    if (!ret) ret = m_objects_model->AddSettingsChild(parent_item);
+
+    m_objects_model->UpdateSettingsDigest(ret, categories);
+    Expand(parent_item);
+
+    return ret;
+}
+
+void ObjectList::add_object_to_list(size_t obj_idx, bool call_selection_changed)
 {
     auto model_object = (*m_objects)[obj_idx];
     const wxString& item_name = from_u8(model_object->name);
@@ -2116,11 +2242,7 @@ void ObjectList::add_object_to_list(size_t obj_idx)
                 !volume->config.has("extruder") ? 0 :
                 volume->config.option<ConfigOptionInt>("extruder")->value,
                 false);
-            auto opt_keys = volume->config.keys();
-            if (!opt_keys.empty() && !(opt_keys.size() == 1 && opt_keys[0] == "extruder")) {
-                select_item(m_objects_model->AddSettingsChild(vol_item));
-                Expand(vol_item);
-            }
+            add_settings_item(vol_item, &volume->config);
         }
         Expand(item);
     }
@@ -2130,17 +2252,14 @@ void ObjectList::add_object_to_list(size_t obj_idx)
         increase_object_instances(obj_idx, model_object->instances.size());
 
     // add settings to the object, if it has those
-    auto opt_keys = model_object->config.keys();
-    if (!opt_keys.empty() && !(opt_keys.size() == 1 && opt_keys[0] == "extruder")) {
-        select_item(m_objects_model->AddSettingsChild(item));
-        Expand(item);
-    }
+    add_settings_item(item, &model_object->config);
 
     // Add layers if it has
     add_layer_root_item(item);
 
 #ifndef __WXOSX__ 
-    selection_changed();
+    if (call_selection_changed)
+	    selection_changed();
 #endif //__WXMSW__
 }
 
@@ -2175,6 +2294,8 @@ void ObjectList::delete_from_model_and_list(const ItemType type, const int obj_i
     if ( !(type&(itObject|itVolume|itInstance)) )
         return;
 
+    take_snapshot(_(L("Delete Selected Item")));
+
     if (type&itObject) {
         del_object(obj_idx);
         delete_object_from_list(obj_idx);
@@ -2285,6 +2406,9 @@ void ObjectList::remove()
 
     wxDataViewItem  parent = wxDataViewItem(0);
 
+    take_snapshot(_(L("Delete Selected")));
+    suppress_snapshots();
+
     for (auto& item : sels)
     {
         if (m_objects_model->GetParent(item) == wxDataViewItem(0))
@@ -2305,6 +2429,8 @@ void ObjectList::remove()
 
     if (parent)
         select_item(parent);
+
+    allow_snapshots();
 }
 
 void ObjectList::del_layer_range(const t_layer_height_range& range)
@@ -2350,6 +2476,8 @@ void ObjectList::add_layer_range_after_current(const t_layer_height_range& curre
     
     if (current_range == last_range)
     {
+        take_snapshot(_(L("Add New Layers Range")));
+
         const t_layer_height_range& new_range = { last_range.second, last_range.second + 2.0f };
         ranges[new_range] = get_default_layer_config(obj_idx);
         add_layer_item(new_range, layers_item);
@@ -2377,22 +2505,28 @@ void ObjectList::add_layer_range_after_current(const t_layer_height_range& curre
             
             t_layer_height_range new_range = { midl_layer, next_range.second };
 
+            take_snapshot(_(L("Add New Layers Range")));
+            suppress_snapshots();
+
+            // create new 2 layers instead of deleted one
+
             // delete old layer
 
             wxDataViewItem layer_item = m_objects_model->GetItemByLayerRange(obj_idx, next_range);
             del_subobject_item(layer_item);
 
-            // create new 2 layers instead of deleted one
-
             ranges[new_range] = old_config;
             add_layer_item(new_range, layers_item, layer_idx);
 
             new_range = { current_range.second, midl_layer };
             ranges[new_range] = get_default_layer_config(obj_idx);
             add_layer_item(new_range, layers_item, layer_idx);
+            allow_snapshots();
         }
         else
         {
+            take_snapshot(_(L("Add New Layers Range")));
+
             const t_layer_height_range new_range = { current_range.second, next_range.first };
             ranges[new_range] = get_default_layer_config(obj_idx);
             add_layer_item(new_range, layers_item, layer_idx);
@@ -2420,9 +2554,7 @@ void ObjectList::add_layer_item(const t_layer_height_range& range,
                                                             range, 
                                                             config.opt_int("extruder"),
                                                             layer_idx);
-
-    if (config.keys().size() > 2)
-        select_item(m_objects_model->AddSettingsChild(layer_item));
+    add_settings_item(layer_item, &config);
 }
 
 bool ObjectList::edit_layer_range(const t_layer_height_range& range, coordf_t layer_height)
@@ -2452,6 +2584,8 @@ bool ObjectList::edit_layer_range(const t_layer_height_range& range, const t_lay
     const int obj_idx = get_selected_obj_idx();
     if (obj_idx < 0) return false;
 
+    take_snapshot(_(L("Edit Layers Range")));
+
     const ItemType sel_type = m_objects_model->GetItemType(GetSelection());
 
     t_layer_config_ranges& ranges = object(obj_idx)->layer_config_ranges;
@@ -2918,6 +3052,8 @@ void ObjectList::change_part_type()
 	if (new_type == type || new_type == ModelVolumeType::INVALID)
         return;
 
+    take_snapshot(_(L("Paste from Clipboard")));
+
     const auto item = GetSelection();
     volume->set_type(new_type);
     m_objects_model->SetVolumeType(item, new_type);
@@ -2933,18 +3069,17 @@ void ObjectList::change_part_type()
     }
     else if (!settings_item && 
               (new_type == ModelVolumeType::MODEL_PART || new_type == ModelVolumeType::PARAMETER_MODIFIER)) {
-        select_item(m_objects_model->AddSettingsChild(item));
+        add_settings_item(item, &volume->config);
     }
 }
 
 void ObjectList::last_volume_is_deleted(const int obj_idx)
 {
 
-    if (obj_idx < 0 || m_objects->empty() ||
-        obj_idx <= m_objects->size() ||
-        (*m_objects)[obj_idx]->volumes.empty())
+    if (obj_idx < 0 || obj_idx >= m_objects->size() || (*m_objects)[obj_idx]->volumes.empty())
         return;
-    auto volume = (*m_objects)[obj_idx]->volumes[0];
+
+    auto volume = (*m_objects)[obj_idx]->volumes.front();
 
     // clear volume's config values
     volume->config.clear();
@@ -2966,6 +3101,7 @@ bool ObjectList::has_multi_part_objects()
     return false;
 }
 
+/* #lm_FIXME_delete_after_testing
 void ObjectList::update_settings_items()
 {
     m_prevent_canvas_selection_update = true;
@@ -2991,22 +3127,52 @@ void ObjectList::update_settings_items()
     SetSelections(sel);
     m_prevent_canvas_selection_update = false;
 }
+*/
+void ObjectList::update_and_show_object_settings_item()
+{
+    const wxDataViewItem item = GetSelection();
+    if (!item) return;
+
+    const wxDataViewItem& obj_item = m_objects_model->IsSettingsItem(item) ? m_objects_model->GetParent(item) : item;
+    select_item(add_settings_item(obj_item, &get_item_config(obj_item)));
+}
 
 // Update settings item for item had it
 void ObjectList::update_settings_item_and_selection(wxDataViewItem item, wxDataViewItemArray& selections)
 {
-    const wxDataViewItem& settings_item = m_objects_model->GetSettingsItem(item);
-    select_item(settings_item ? settings_item : m_objects_model->AddSettingsChild(item));
+    const wxDataViewItem old_settings_item = m_objects_model->GetSettingsItem(item);
+    const wxDataViewItem new_settings_item = add_settings_item(item, &get_item_config(item));
 
-    // If settings item was deleted from the list, 
-    // it's need to be deleted from selection array, if it was there
-    if (settings_item != m_objects_model->GetSettingsItem(item) &&
-        selections.Index(settings_item) != wxNOT_FOUND) {
-        selections.Remove(settings_item);
+    if (!new_settings_item && old_settings_item)
+        m_objects_model->Delete(old_settings_item);
+
+    // if ols settings item was is selected area
+    if (selections.Index(old_settings_item) != wxNOT_FOUND)
+    {
+        // If settings item was just updated
+        if (old_settings_item == new_settings_item)
+        {
+            Sidebar& panel = wxGetApp().sidebar();
+            panel.Freeze();
 
-        // Select item, if settings_item doesn't exist for item anymore, but was selected
-        if (selections.Index(item) == wxNOT_FOUND)
-            selections.Add(item);
+            // update settings list
+            wxGetApp().obj_settings()->UpdateAndShow(true);
+
+            panel.Layout();
+            panel.Thaw();
+        }
+        else
+        // If settings item was deleted from the list, 
+        // it's need to be deleted from selection array, if it was there
+        {
+            selections.Remove(old_settings_item);
+
+            // Select item, if settings_item doesn't exist for item anymore, but was selected
+            if (selections.Index(item) == wxNOT_FOUND) {
+                selections.Add(item);
+                select_item(item); // to correct update of the SettingsList and ManipulationPanel sizers
+            }
+        }
     }
 }
 
@@ -3360,6 +3526,35 @@ void ObjectList::set_extruder_for_selected_items(const int extruder) const
     wxGetApp().plater()->update();
 }
 
+void ObjectList::update_after_undo_redo()
+{
+    m_prevent_list_events = true;
+    m_prevent_canvas_selection_update = true;
+
+    suppress_snapshots();
+
+    // Unselect all objects before deleting them, so that no change of selection is emitted during deletion.
+    this->UnselectAll();
+    m_objects_model->DeleteAll();
+
+    size_t obj_idx = 0;
+    while (obj_idx < m_objects->size()) {
+        add_object_to_list(obj_idx, false);
+        ++obj_idx;
+    }
+
+    allow_snapshots();
+
+#ifndef __WXOSX__ 
+    selection_changed();
+#endif /* __WXOSX__ */
+
+    update_selections();
+
+    m_prevent_canvas_selection_update = false;
+    m_prevent_list_events = false;
+}
+
 ModelObject* ObjectList::object(const int obj_idx) const
 {
     if (obj_idx < 0)
diff --git a/src/slic3r/GUI/GUI_ObjectList.hpp b/src/slic3r/GUI/GUI_ObjectList.hpp
index ed19edd62..2d7e9f5f1 100644
--- a/src/slic3r/GUI/GUI_ObjectList.hpp
+++ b/src/slic3r/GUI/GUI_ObjectList.hpp
@@ -26,7 +26,7 @@ enum class ModelVolumeType : int;
 // FIXME: broken build on mac os because of this is missing:
 typedef std::vector<std::string>    t_config_option_keys;
 
-typedef std::map<std::string, std::vector<std::string>> FreqSettingsBundle;
+typedef std::map<std::string, std::vector<std::string>> SettingsBundle;
 
 //				  category ->		vector 			 ( option	;  label )
 typedef std::map< std::string, std::vector< std::pair<std::string, std::string> > > settings_menu_hierarchy;
@@ -152,8 +152,8 @@ class ObjectList : public wxDataViewCtrl
     wxDataViewItem m_last_selected_item {nullptr};
 
 #if 0
-    FreqSettingsBundle m_freq_settings_fff;
-    FreqSettingsBundle m_freq_settings_sla;
+    SettingsBundle m_freq_settings_fff;
+    SettingsBundle m_freq_settings_sla;
 #endif
 
 public:
@@ -204,10 +204,12 @@ public:
 
     void                copy();
     void                paste();
+    void                undo();
+    void                redo();
 
     void                get_settings_choice(const wxString& category_name);
     void                get_freq_settings_choice(const wxString& bundle_name);
-    void                update_settings_item();
+    void                show_settings(const wxDataViewItem settings_item);
 
     wxMenu*             append_submenu_add_generic(wxMenu* menu, const ModelVolumeType type);
     void                append_menu_items_add_volume(wxMenu* menu);
@@ -245,6 +247,7 @@ public:
     void                layers_editing();
 
     wxDataViewItem      add_layer_root_item(const wxDataViewItem obj_item);
+    wxDataViewItem      add_settings_item(wxDataViewItem parent_item, const DynamicPrintConfig* config);
 
     DynamicPrintConfig  get_default_layer_config(const int obj_idx);
     bool                get_volume_by_item(const wxDataViewItem& item, ModelVolume*& volume);
@@ -256,12 +259,13 @@ public:
     wxBoxSizer*         get_sizer() {return  m_sizer;}
     int                 get_selected_obj_idx() const;
     DynamicPrintConfig& get_item_config(const wxDataViewItem& item) const;
+    SettingsBundle      get_item_settings_bundle(const DynamicPrintConfig* config, const bool is_layers_range_settings);
 
     void                changed_object(const int obj_idx = -1) const;
     void                part_selection_changed();
 
     // Add object to the list
-    void add_object_to_list(size_t obj_idx);
+    void add_object_to_list(size_t obj_idx, bool call_selection_changed = true);
     // Delete object from the list
     void delete_object_from_list();
     void delete_object_from_list(const size_t obj_idx);
@@ -315,6 +319,7 @@ public:
     void last_volume_is_deleted(const int obj_idx);
     bool has_multi_part_objects();
     void update_settings_items();
+    void update_and_show_object_settings_item();
     void update_settings_item_and_selection(wxDataViewItem item, wxDataViewItemArray& selections);
     void update_object_list_by_printer_technology();
     void update_object_menu();
@@ -333,6 +338,8 @@ public:
 
     void msw_rescale();
 
+    void update_after_undo_redo();
+
 private:
 #ifdef __WXOSX__
 //    void OnChar(wxKeyEvent& event);
diff --git a/src/slic3r/GUI/GUI_ObjectManipulation.cpp b/src/slic3r/GUI/GUI_ObjectManipulation.cpp
index 5dc11170b..1141ad907 100644
--- a/src/slic3r/GUI/GUI_ObjectManipulation.cpp
+++ b/src/slic3r/GUI/GUI_ObjectManipulation.cpp
@@ -242,8 +242,7 @@ ObjectManipulation::ObjectManipulation(wxWindow* parent) :
                 selection.synchronize_unselected_instances(Selection::SYNC_ROTATION_GENERAL);
                 selection.synchronize_unselected_volumes();
                 // Copy mirroring values from GLVolumes into Model (ModelInstance / ModelVolume), trigger background processing.
-                canvas->do_mirror();
-                canvas->set_as_dirty();
+                canvas->do_mirror("Set Mirror");
                 UpdateAndShow(true);
             });
         return sizer;
@@ -324,7 +323,7 @@ ObjectManipulation::ObjectManipulation(wxWindow* parent) :
                     selection.synchronize_unselected_instances(Selection::SYNC_ROTATION_GENERAL);
                     selection.synchronize_unselected_volumes();
                     // Copy rotation values from GLVolumes into Model (ModelInstance / ModelVolume), trigger background processing.
-                    canvas->do_rotate();
+                    canvas->do_rotate("Set Rotation");
 
                     UpdateAndShow(true);
                 });
@@ -710,7 +709,7 @@ void ObjectManipulation::change_position_value(int axis, double value)
     Selection& selection = canvas->get_selection();
     selection.start_dragging();
     selection.translate(position - m_cache.position, selection.requires_local_axes());
-    canvas->do_move();
+    canvas->do_move("Set Position");
 
     m_cache.position = position;
 	m_cache.position_rounded(axis) = DBL_MAX;
@@ -741,7 +740,7 @@ void ObjectManipulation::change_rotation_value(int axis, double value)
 	selection.rotate(
 		(M_PI / 180.0) * (transformation_type.absolute() ? rotation : rotation - m_cache.rotation), 
 		transformation_type);
-    canvas->do_rotate();
+    canvas->do_rotate("Set Orientation");
 
     m_cache.rotation = rotation;
 	m_cache.rotation_rounded(axis) = DBL_MAX;
@@ -806,7 +805,7 @@ void ObjectManipulation::do_scale(int axis, const Vec3d &scale) const
 
     selection.start_dragging();
     selection.scale(scaling_factor * 0.01, transformation_type);
-    wxGetApp().plater()->canvas3D()->do_scale();
+    wxGetApp().plater()->canvas3D()->do_scale("Set Scale");
 }
 
 void ObjectManipulation::on_change(t_config_option_key opt_key, const boost::any& value)
diff --git a/src/slic3r/GUI/GUI_ObjectSettings.cpp b/src/slic3r/GUI/GUI_ObjectSettings.cpp
index ab2614895..16c64360a 100644
--- a/src/slic3r/GUI/GUI_ObjectSettings.cpp
+++ b/src/slic3r/GUI/GUI_ObjectSettings.cpp
@@ -63,20 +63,28 @@ ObjectSettings::ObjectSettings(wxWindow* parent) :
     m_bmp_delete = ScalableBitmap(parent, "cross");
 }
 
-void ObjectSettings::update_settings_list()
+bool ObjectSettings::update_settings_list()
 {
     m_settings_list_sizer->Clear(true);
+    m_og_settings.resize(0);
 
     auto objects_ctrl   = wxGetApp().obj_list();
     auto objects_model  = wxGetApp().obj_list()->GetModel();
     auto config         = wxGetApp().obj_list()->config();
 
     const auto item = objects_ctrl->GetSelection();
+    
+    if (!item || !objects_model->IsSettingsItem(item) || !config || objects_ctrl->multiple_selection())
+        return false;
+
     const bool is_layers_range_settings = objects_model->GetItemType(objects_model->GetParent(item)) == itLayer;
+	SettingsBundle cat_options = objects_ctrl->get_item_settings_bundle(config, is_layers_range_settings);
+
+    if (!cat_options.empty())
+    {
+	    std::vector<std::string> categories;
+        categories.reserve(cat_options.size());
 
-    if (item && !objects_ctrl->multiple_selection() && 
-        config && objects_model->IsSettingsItem(item))
-	{
         auto extra_column = [config, this](wxWindow* parent, const Line& line)
 		{
 			auto opt_key = (line.get_options())[0].opt_id;  //we assume that we have one option per line
@@ -96,86 +104,61 @@ void ObjectSettings::update_settings_list()
 			return btn;
 		};
 
-		std::map<std::string, std::vector<std::string>> cat_options;
-		auto opt_keys = config->keys();
-        objects_ctrl->update_opt_keys(opt_keys); // update options list according to print technology
-
-        m_og_settings.resize(0);
-        std::vector<std::string> categories;
-        if (!(opt_keys.size() == 1 && opt_keys[0] == "extruder"))// return;
+        for (auto& cat : cat_options)
         {
-            const int extruders_cnt = wxGetApp().preset_bundle->printers.get_selected_preset().printer_technology() == ptSLA ? 1 :
-                wxGetApp().preset_bundle->printers.get_edited_preset().config.option<ConfigOptionFloats>("nozzle_diameter")->values.size();
-
-            for (auto& opt_key : opt_keys) {
-                auto category = config->def()->get(opt_key)->category;
-                if (category.empty() ||
-                    (category == "Extruders" && extruders_cnt == 1)) continue;
-
-                std::vector< std::string > new_category;
-
-                auto& cat_opt = cat_options.find(category) == cat_options.end() ? new_category : cat_options.at(category);
-                cat_opt.push_back(opt_key);
-                if (cat_opt.size() == 1)
-                    cat_options[category] = cat_opt;
-            }
-
-            for (auto& cat : cat_options) {
-                if (cat.second.size() == 1 && 
-                    (cat.second[0] == "extruder" || is_layers_range_settings && cat.second[0] == "layer_height"))
+            if (cat.second.size() == 1 &&
+                (cat.second[0] == "extruder" || is_layers_range_settings && cat.second[0] == "layer_height"))
+                continue;
+
+            categories.push_back(cat.first);
+
+            auto optgroup = std::make_shared<ConfigOptionsGroup>(m_og->ctrl_parent(), _(cat.first), config, false, extra_column);
+            optgroup->label_width = 15;
+            optgroup->sidetext_width = 5.5;
+
+            optgroup->m_on_change = [](const t_config_option_key& opt_id, const boost::any& value) {
+                                    wxGetApp().obj_list()->changed_object(); };
+
+            // call back for rescaling of the extracolumn control
+            optgroup->rescale_extra_column_item = [this](wxWindow* win) {
+                auto *ctrl = dynamic_cast<ScalableButton*>(win);
+                if (ctrl == nullptr)
+                    return;
+                ctrl->SetBitmap_(m_bmp_delete);
+            };
+
+            const bool is_extruders_cat = cat.first == "Extruders";
+            for (auto& opt : cat.second)
+            {
+                if (opt == "extruder" || is_layers_range_settings && opt == "layer_height")
                     continue;
-
-                auto optgroup = std::make_shared<ConfigOptionsGroup>(m_og->ctrl_parent(), _(cat.first), config, false, extra_column);
-                optgroup->label_width = 15;
-                optgroup->sidetext_width = 5.5;
-
-                optgroup->m_on_change = [](const t_config_option_key& opt_id, const boost::any& value) {
-                                        wxGetApp().obj_list()->changed_object(); };
-
-                const bool is_extruders_cat = cat.first == "Extruders";
-                for (auto& opt : cat.second)
-                {
-                    if (opt == "extruder" || is_layers_range_settings && opt == "layer_height")
-                        continue;
-                    Option option = optgroup->get_option(opt);
-                    option.opt.width = 12;
-                    if (is_extruders_cat)
-                        option.opt.max = wxGetApp().extruders_cnt();
-                    optgroup->append_single_option_line(option);
-                }
-                optgroup->reload_config();
-                m_settings_list_sizer->Add(optgroup->sizer, 0, wxEXPAND | wxALL, 0);
-
-                // call back for rescaling of the extracolumn control
-                optgroup->rescale_extra_column_item = [this](wxWindow* win) {
-                    auto *ctrl = dynamic_cast<ScalableButton*>(win);
-                    if (ctrl == nullptr)
-                        return;
-                    ctrl->SetBitmap_(m_bmp_delete);
-                };
-
-                m_og_settings.push_back(optgroup);
-
-                categories.push_back(cat.first);
+                Option option = optgroup->get_option(opt);
+                option.opt.width = 12;
+                if (is_extruders_cat)
+                    option.opt.max = wxGetApp().extruders_edited_cnt();
+                optgroup->append_single_option_line(option);
             }
-        }
+            optgroup->reload_config();
 
-        if (m_og_settings.empty()) {
-            objects_ctrl->select_item(objects_model->Delete(item));
+            m_settings_list_sizer->Add(optgroup->sizer, 0, wxEXPAND | wxALL, 0);
+            m_og_settings.push_back(optgroup);
         }
-        else {
-            if (!categories.empty())
-                objects_model->UpdateSettingsDigest(item, categories);
-        }
-	}
+
+        if (!categories.empty())
+            objects_model->UpdateSettingsDigest(item, categories);
+    }
+    else
+    {
+        objects_ctrl->select_item(objects_model->Delete(item));
+        return false;
+    } 
+            
+    return true;
 }
 
 void ObjectSettings::UpdateAndShow(const bool show)
 {
-    if (show)
-        update_settings_list();
-
-    OG_Settings::UpdateAndShow(show);
+    OG_Settings::UpdateAndShow(show ? update_settings_list() : false);
 }
 
 void ObjectSettings::msw_rescale()
diff --git a/src/slic3r/GUI/GUI_ObjectSettings.hpp b/src/slic3r/GUI/GUI_ObjectSettings.hpp
index 3d49f13b7..01daa5622 100644
--- a/src/slic3r/GUI/GUI_ObjectSettings.hpp
+++ b/src/slic3r/GUI/GUI_ObjectSettings.hpp
@@ -44,7 +44,7 @@ public:
     ObjectSettings(wxWindow* parent);
     ~ObjectSettings() {}
 
-    void        update_settings_list();
+    bool        update_settings_list();
     void        UpdateAndShow(const bool show) override;
     void        msw_rescale();
 };
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
index 7b6cb0cc2..fdc15e928 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
@@ -379,7 +379,7 @@ bool GLGizmoSlaSupports::is_point_clipped(const Vec3d& point) const
 bool GLGizmoSlaSupports::is_mesh_update_necessary() const
 {
     return ((m_state == On) && (m_model_object != nullptr) && !m_model_object->instances.empty())
-        && ((m_model_object->id() != m_current_mesh_model_id) || m_its == nullptr);
+        && ((m_model_object->id() != m_current_mesh_object_id) || m_its == nullptr);
 }
 
 void GLGizmoSlaSupports::update_mesh()
@@ -389,7 +389,7 @@ void GLGizmoSlaSupports::update_mesh()
     // This mesh does not account for the possible Z up SLA offset.
     m_mesh = &m_model_object->volumes.front()->mesh();
     m_its = &m_mesh->its;
-    m_current_mesh_model_id = m_model_object->id();
+    m_current_mesh_object_id = m_model_object->id();
     m_editing_mode = false;
 
 	m_AABB.deinit();
@@ -923,10 +923,12 @@ RENDER_AGAIN:
         }
 
         if (value_changed) { // Update side panel
-            wxTheApp->CallAfter([]() {
-                wxGetApp().obj_settings()->UpdateAndShow(true);
-                wxGetApp().obj_list()->update_settings_items();
-            });
+/*            wxTheApp->CallAfter([]() {
+ *                wxGetApp().obj_settings()->UpdateAndShow(true);
+ *                wxGetApp().obj_list()->update_settings_items();
+ *            });
+ * #lm_FIXME_delete_after_testing */
+            wxGetApp().obj_list()->update_and_show_object_settings_item();
         }
 
         bool generate = m_imgui->button(m_desc.at("auto_generate"));
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
index f4b2fbb0e..5e50eae0b 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
@@ -26,7 +26,7 @@ class GLGizmoSlaSupports : public GLGizmoBase
 {
 private:
     ModelObject* m_model_object = nullptr;
-    ModelID m_current_mesh_model_id = 0;
+    ObjectID m_current_mesh_object_id = 0;
     int m_active_instance = -1;
     float m_active_instance_bb_radius; // to cache the bb
     mutable float m_z_shift = 0.f;
diff --git a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
index 315027dad..602235d4a 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
@@ -542,8 +542,7 @@ bool GLGizmosManager::on_mouse(wxMouseEvent& evt, GLCanvas3D& canvas)
                 if (m_current == Flatten)
                 {
                     // Rotate the object so the normal points downward:
-                    selection.flattening_rotate(get_flattening_normal());
-                    canvas.do_flatten();
+                    canvas.do_flatten(get_flattening_normal(), "Place on Face");
                     wxGetApp().obj_manipul()->set_dirty();
                 }
 
@@ -616,17 +615,17 @@ bool GLGizmosManager::on_mouse(wxMouseEvent& evt, GLCanvas3D& canvas)
             case Move:
             {
                 canvas.disable_regenerate_volumes();
-                canvas.do_move();
+                canvas.do_move("Gizmo-Move Object");
                 break;
             }
             case Scale:
             {
-                canvas.do_scale();
+                canvas.do_scale("Gizmo-Scale Object");
                 break;
             }
             case Rotate:
             {
-                canvas.do_rotate();
+                canvas.do_rotate("Gizmo-Rotate Object");
                 break;
             }
             default:
diff --git a/src/slic3r/GUI/ImGuiWrapper.cpp b/src/slic3r/GUI/ImGuiWrapper.cpp
index b6abf641a..f58266a5d 100644
--- a/src/slic3r/GUI/ImGuiWrapper.cpp
+++ b/src/slic3r/GUI/ImGuiWrapper.cpp
@@ -233,9 +233,9 @@ ImVec2 ImGuiWrapper::calc_text_size(const wxString &text)
     return size;
 }
 
-void ImGuiWrapper::set_next_window_pos(float x, float y, int flag)
+void ImGuiWrapper::set_next_window_pos(float x, float y, int flag, float pivot_x, float pivot_y)
 {
-    ImGui::SetNextWindowPos(ImVec2(x, y), (ImGuiCond)flag);
+    ImGui::SetNextWindowPos(ImVec2(x, y), (ImGuiCond)flag, ImVec2(pivot_x, pivot_y));
     ImGui::SetNextWindowSize(ImVec2(0.0, 0.0));
 }
 
@@ -342,6 +342,32 @@ bool ImGuiWrapper::combo(const wxString& label, const std::vector<std::string>&
     return res;
 }
 
+bool ImGuiWrapper::undo_redo_list(const ImVec2& size, const bool is_undo, bool (*items_getter)(const bool , int , const char**), int& hovered, int& selected)
+{
+    bool is_hovered = false;
+    ImGui::ListBoxHeader("", size);
+
+    int i=0;
+    const char* item_text;
+    while (items_getter(is_undo, i, &item_text))
+    {
+        ImGui::Selectable(item_text, i < hovered);
+
+        if (ImGui::IsItemHovered()) {
+            ImGui::SetTooltip(item_text);
+            hovered = i;
+            is_hovered = true;
+        }
+
+        if (ImGui::IsItemClicked())
+            selected = i;
+        i++;
+    }
+
+    ImGui::ListBoxFooter();
+    return is_hovered;
+}
+
 void ImGuiWrapper::disabled_begin(bool disabled)
 {
     wxCHECK_RET(!m_disabled, "ImGUI: Unbalanced disabled_begin() call");
diff --git a/src/slic3r/GUI/ImGuiWrapper.hpp b/src/slic3r/GUI/ImGuiWrapper.hpp
index 0479e4743..c6550351e 100644
--- a/src/slic3r/GUI/ImGuiWrapper.hpp
+++ b/src/slic3r/GUI/ImGuiWrapper.hpp
@@ -51,7 +51,7 @@ public:
     ImVec2 scaled(float x, float y) const { return ImVec2(x * m_font_size, y * m_font_size); }
     ImVec2 calc_text_size(const wxString &text);
 
-    void set_next_window_pos(float x, float y, int flag);
+    void set_next_window_pos(float x, float y, int flag, float pivot_x = 0.0f, float pivot_y = 0.0f);
     void set_next_window_bg_alpha(float alpha);
 
     bool begin(const std::string &name, int flags = 0);
@@ -67,6 +67,7 @@ public:
     void text(const std::string &label);
     void text(const wxString &label);
     bool combo(const wxString& label, const std::vector<std::string>& options, int& selection);   // Use -1 to not mark any option as selected
+    bool undo_redo_list(const ImVec2& size, const bool is_undo, bool (*items_getter)(const bool, int, const char**), int& hovered, int& selected);
 
     void disabled_begin(bool disabled);
     void disabled_end();
diff --git a/src/slic3r/GUI/MainFrame.cpp b/src/slic3r/GUI/MainFrame.cpp
index 99389da41..b08df1690 100644
--- a/src/slic3r/GUI/MainFrame.cpp
+++ b/src/slic3r/GUI/MainFrame.cpp
@@ -538,6 +538,14 @@ void MainFrame::init_menubar()
             menu_icon("delete_all_menu"), nullptr, [this](){return can_delete_all(); }, this);
 
         editMenu->AppendSeparator();
+        append_menu_item(editMenu, wxID_ANY, _(L("&Undo")) + sep + GUI::shortkey_ctrl_prefix() + sep_space + "Z",
+            _(L("Undo")), [this](wxCommandEvent&) { m_plater->undo(); },
+            "undo", nullptr, [this](){return m_plater->can_undo(); }, this);
+        append_menu_item(editMenu, wxID_ANY, _(L("&Redo")) + sep + GUI::shortkey_ctrl_prefix() + sep_space + "Y",
+            _(L("Redo")), [this](wxCommandEvent&) { m_plater->redo(); },
+            "redo", nullptr, [this](){return m_plater->can_redo(); }, this);
+
+        editMenu->AppendSeparator();
         append_menu_item(editMenu, wxID_ANY, _(L("&Copy")) + sep + GUI::shortkey_ctrl_prefix() + sep_space + "C",
             _(L("Copy selection to clipboard")), [this](wxCommandEvent&) { m_plater->copy_selection_to_clipboard(); },
             menu_icon("copy_menu"), nullptr, [this](){return m_plater->can_copy_to_clipboard(); }, this);
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index 8c074709f..f5f245471 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -70,6 +70,7 @@
 #include "../Utils/ASCIIFolding.hpp"
 #include "../Utils/PrintHost.hpp"
 #include "../Utils/FixModelByWin10.hpp"
+#include "../Utils/UndoRedo.hpp"
 
 #include <wx/glcanvas.h>    // Needs to be last because reasons :-/
 #include "WipeTowerDialog.hpp"
@@ -1254,6 +1255,8 @@ const std::regex PlaterDropTarget::pattern_drop(".*[.](stl|obj|amf|3mf|prusa)",
 
 bool PlaterDropTarget::OnDropFiles(wxCoord x, wxCoord y, const wxArrayString &filenames)
 {
+	plater->take_snapshot(_(L("Load Files")));
+
     std::vector<fs::path> paths;
 
     for (const auto &filename : filenames) {
@@ -1319,7 +1322,12 @@ struct Plater::priv
     Slic3r::Model               model;
     PrinterTechnology           printer_technology = ptFFF;
     Slic3r::GCodePreviewData    gcode_preview_data;
-
+    Slic3r::UndoRedo::Stack 	undo_redo_stack;
+    int                         m_prevent_snapshots = 0;     /* Used for avoid of excess "snapshoting". 
+                                                              * Like for "delete selected" or "set numbers of copies"
+                                                              * we should call tack_snapshot just ones 
+                                                              * instead of calls for each action separately
+                                                              * */
     // GUI elements
     wxSizer* panel_sizer{ nullptr };
     wxPanel* current_panel{ nullptr };
@@ -1619,6 +1627,23 @@ struct Plater::priv
     void split_object();
     void split_volume();
     void scale_selection_to_fit_print_volume();
+
+	void take_snapshot(const std::string& snapshot_name)
+	{
+        if (this->m_prevent_snapshots > 0) 
+            return;
+        assert(this->m_prevent_snapshots >= 0);
+	    this->undo_redo_stack.take_snapshot(snapshot_name, model, view3D->get_canvas3d()->get_selection());
+	}
+	void take_snapshot(const wxString& snapshot_name) { this->take_snapshot(std::string(snapshot_name.ToUTF8().data())); }
+    int  get_active_snapshot_index();
+    void undo();
+    void redo();
+    void undo_to(size_t time_to_load);
+    void redo_to(size_t time_to_load);
+    void suppress_snapshots()   { this->m_prevent_snapshots++; }
+    void allow_snapshots()      { this->m_prevent_snapshots--; }
+
     bool background_processing_enabled() const { return this->get_config("background_processing") == "1"; }
     void update_print_volume_state();
     void schedule_background_process();
@@ -1709,6 +1734,7 @@ private:
 
     void update_fff_scene();
     void update_sla_scene();
+    void update_after_undo_redo();
 
     // path to project file stored with no extension
     wxString m_project_filename;
@@ -1811,6 +1837,8 @@ Plater::priv::priv(Plater *q, MainFrame *main_frame)
     view3D_canvas->Bind(EVT_GLCANVAS_MOUSE_DRAGGING_FINISHED, &priv::on_3dcanvas_mouse_dragging_finished, this);
     view3D_canvas->Bind(EVT_GLCANVAS_TAB, [this](SimpleEvent&) { select_next_view_3D(); });
     view3D_canvas->Bind(EVT_GLCANVAS_RESETGIZMOS, [this](SimpleEvent&) { reset_all_gizmos(); });
+    view3D_canvas->Bind(EVT_GLCANVAS_UNDO, [this](SimpleEvent&) { this->undo(); });
+    view3D_canvas->Bind(EVT_GLCANVAS_REDO, [this](SimpleEvent&) { this->redo(); });
 
     // 3DScene/Toolbar:
     view3D_canvas->Bind(EVT_GLTOOLBAR_ADD, &priv::on_action_add, this);
@@ -1849,6 +1877,9 @@ Plater::priv::priv(Plater *q, MainFrame *main_frame)
 
     // updates camera type from .ini file
     camera.set_type(get_config("use_perspective_camera"));
+
+    // Initialize the Undo / Redo stack with a first snapshot.
+	this->take_snapshot(_(L("New Project")));
 }
 
 Plater::priv::~priv()
@@ -2219,7 +2250,7 @@ std::vector<size_t> Plater::priv::load_model_objects(const ModelObjectPtrs &mode
             // the size of the object is too big -> this could lead to overflow when moving to clipper coordinates,
             // so scale down the mesh
 			double inv = 1. / max_ratio;
-            object->scale_mesh(Vec3d(inv, inv, inv));
+            object->scale_mesh_after_creation(Vec3d(inv, inv, inv));
             object->origin_translation = Vec3d::Zero();
             object->center_around_origin();
             scaled_down = true;
@@ -2398,12 +2429,15 @@ void Plater::priv::object_list_changed()
 
 void Plater::priv::select_all()
 {
+//    this->take_snapshot(_(L("Select All")));
+
     view3D->select_all();
     this->sidebar->obj_list()->update_selections();
 }
 
 void Plater::priv::deselect_all()
 {
+//    this->take_snapshot(_(L("Deselect All")));
     view3D->deselect_all();
 }
 
@@ -2425,6 +2459,7 @@ void Plater::priv::remove(size_t obj_idx)
 
 void Plater::priv::delete_object_from_model(size_t obj_idx)
 {
+    this->take_snapshot(_(L("Delete Object")));
     model.delete_object(obj_idx);
     update();
     object_list_changed();
@@ -2432,6 +2467,8 @@ void Plater::priv::delete_object_from_model(size_t obj_idx)
 
 void Plater::priv::reset()
 {
+	this->take_snapshot(_(L("Reset Project")));
+
     set_project_filename(wxEmptyString);
 
     // Prevent toolpaths preview from rendering while we modify the Print object
@@ -2457,17 +2494,20 @@ void Plater::priv::reset()
 
 void Plater::priv::mirror(Axis axis)
 {
+    this->take_snapshot(_(L("Mirror")));
     view3D->mirror_selection(axis);
 }
 
 void Plater::priv::arrange()
 {
+    this->take_snapshot(_(L("Arrange")));
     m_ui_jobs.start(Jobs::Arrange);
 }
 
 // This method will find an optimal orientation for the currently selected item
 // Very similar in nature to the arrange method above...
 void Plater::priv::sla_optimize_rotation() {
+    this->take_snapshot(_(L("Optimize Rotation")));
     m_ui_jobs.start(Jobs::Rotoptimize);
 }
 
@@ -2623,6 +2663,8 @@ void Plater::priv::split_object()
         Slic3r::GUI::warning_catcher(q, _(L("The selected object couldn't be split because it contains only one part.")));
     else
     {
+        this->take_snapshot(_(L("Split to Objects")));
+
         unsigned int counter = 1;
         for (ModelObject* m : new_objects)
             m->name = current_model_object->name + "_" + std::to_string(counter++);
@@ -2861,6 +2903,8 @@ void Plater::priv::update_sla_scene()
 
 void Plater::priv::reload_from_disk()
 {
+    this->take_snapshot(_(L("Reload from Disk")));
+
     const auto &selection = get_selection();
     const auto obj_orig_idx = selection.get_object_idx();
     if (selection.is_wipe_tower() || obj_orig_idx == -1) { return; }
@@ -2894,6 +2938,9 @@ void Plater::priv::fix_through_netfabb(const int obj_idx, const int vol_idx/* =
 {
     if (obj_idx < 0)
         return;
+
+    this->take_snapshot(_(L("Fix Throught NetFabb")));
+
     fix_model_by_win10_sdk_gui(*model.objects[obj_idx], vol_idx);
     this->update();
     this->object_list_changed();
@@ -3139,6 +3186,8 @@ void Plater::priv::on_action_layersediting(SimpleEvent&)
 
 void Plater::priv::on_object_select(SimpleEvent& evt)
 {
+//    this->take_snapshot(_(L("Object Selection")));
+
     wxGetApp().obj_list()->update_selections();
     selection_changed();
 }
@@ -3414,8 +3463,7 @@ void Plater::priv::init_view_toolbar()
     item.icon_filename = "editor.svg";
     item.tooltip = _utf8(L("3D editor view")) + " [" + GUI::shortkey_ctrl_prefix() + "5]";
     item.sprite_id = 0;
-    item.action_callback = [this]() { if (this->q != nullptr) wxPostEvent(this->q, SimpleEvent(EVT_GLVIEWTOOLBAR_3D)); };
-    item.is_toggable = false;
+    item.left.action_callback = [this]() { if (this->q != nullptr) wxPostEvent(this->q, SimpleEvent(EVT_GLVIEWTOOLBAR_3D)); };
     if (!view_toolbar.add_item(item))
         return;
 
@@ -3423,8 +3471,7 @@ void Plater::priv::init_view_toolbar()
     item.icon_filename = "preview.svg";
     item.tooltip = _utf8(L("Preview")) + " [" + GUI::shortkey_ctrl_prefix() + "6]";
     item.sprite_id = 1;
-    item.action_callback = [this]() { if (this->q != nullptr) wxPostEvent(this->q, SimpleEvent(EVT_GLVIEWTOOLBAR_PREVIEW)); };
-    item.is_toggable = false;
+    item.left.action_callback = [this]() { if (this->q != nullptr) wxPostEvent(this->q, SimpleEvent(EVT_GLVIEWTOOLBAR_PREVIEW)); };
     if (!view_toolbar.add_item(item))
         return;
 
@@ -3554,6 +3601,51 @@ void Plater::priv::show_action_buttons(const bool is_ready_to_slice) const
 	}
 }
 
+int Plater::priv::get_active_snapshot_index()
+{
+    const size_t& active_snapshot_time = this->undo_redo_stack.active_snapshot_time();
+    const std::vector<UndoRedo::Snapshot>& ss_stack = this->undo_redo_stack.snapshots();
+    const auto it = std::lower_bound(ss_stack.begin(), ss_stack.end(), UndoRedo::Snapshot(active_snapshot_time));
+    return it - ss_stack.begin();
+}
+
+void Plater::priv::undo()
+{
+	if (this->undo_redo_stack.undo(model, this->view3D->get_canvas3d()->get_selection()))
+		this->update_after_undo_redo();
+}
+
+void Plater::priv::redo()
+{ 
+	if (this->undo_redo_stack.redo(model))
+		this->update_after_undo_redo();
+}
+
+void Plater::priv::undo_to(size_t time_to_load)
+{
+	if (this->undo_redo_stack.undo(model, this->view3D->get_canvas3d()->get_selection(), time_to_load))
+		this->update_after_undo_redo();
+}
+
+void Plater::priv::redo_to(size_t time_to_load)
+{ 
+	if (this->undo_redo_stack.redo(model, time_to_load))
+		this->update_after_undo_redo();
+}
+
+void Plater::priv::update_after_undo_redo()
+{
+	this->view3D->get_canvas3d()->get_selection().clear();
+	this->update(false); // update volumes from the deserializd model
+	//YS_FIXME update obj_list from the deserialized model (maybe store ObjectIDs into the tree?) (no selections at this point of time)
+    this->view3D->get_canvas3d()->get_selection().set_deserialized(GUI::Selection::EMode(this->undo_redo_stack.selection_deserialized().mode), this->undo_redo_stack.selection_deserialized().volumes_and_instances);
+
+    wxGetApp().obj_list()->update_after_undo_redo();
+
+	//FIXME what about the state of the manipulators?
+	//FIXME what about the focus? Cursor in the side panel?
+}
+
 void Sidebar::set_btn_label(const ActionButtonType btn_type, const wxString& label) const
 {
     switch (btn_type)
@@ -3591,6 +3683,8 @@ void Plater::new_project()
 
 void Plater::load_project()
 {
+	this->take_snapshot(_(L("Load Project")));
+
     wxString input_file;
     wxGetApp().load_project(this, input_file);
     load_project(input_file);
@@ -3616,6 +3710,8 @@ void Plater::add_model()
     if (input_files.empty())
         return;
 
+    this->take_snapshot(_(L("Add object(s)")));
+
     std::vector<fs::path> input_paths;
     for (const auto &file : input_files) {
         input_paths.push_back(into_path(file));
@@ -3673,13 +3769,18 @@ void Plater::delete_object_from_model(size_t obj_idx) { p->delete_object_from_mo
 
 void Plater::remove_selected()
 {
+	this->take_snapshot(_(L("Delete Selected Objects")));
+    this->suppress_snapshots();
     this->p->view3D->delete_selected();
+    this->allow_snapshots();
 }
 
 void Plater::increase_instances(size_t num)
 {
     if (! can_increase_instances()) { return; }
 
+	this->take_snapshot(_(L("Increase Instances")));
+
     int obj_idx = p->get_selected_object_idx();
 
     ModelObject* model_object = p->model.objects[obj_idx];
@@ -3714,6 +3815,8 @@ void Plater::decrease_instances(size_t num)
 {
     if (! can_decrease_instances()) { return; }
 
+	this->take_snapshot(_(L("Decrease Instances")));
+
     int obj_idx = p->get_selected_object_idx();
 
     ModelObject* model_object = p->model.objects[obj_idx];
@@ -3748,11 +3851,16 @@ void Plater::set_number_of_copies(/*size_t num*/)
     if (num < 0)
         return;
 
+    this->take_snapshot(wxString::Format(_(L("Set numbers of copies to %d")), num));
+    this->suppress_snapshots();
+
     int diff = (int)num - (int)model_object->instances.size();
     if (diff > 0)
         increase_instances(diff);
     else if (diff < 0)
         decrease_instances(-diff);
+
+    this->allow_snapshots();
 }
 
 bool Plater::is_selection_empty() const
@@ -3776,6 +3884,8 @@ void Plater::cut(size_t obj_idx, size_t instance_idx, coordf_t z, bool keep_uppe
         return;
     }
 
+    this->take_snapshot(_(L("Cut")));
+
     wxBusyCursor wait;
     const auto new_objects = object->cut(instance_idx, z, keep_upper, keep_lower, rotate_lower);
 
@@ -4065,6 +4175,45 @@ void Plater::send_gcode()
     }
 }
 
+void Plater::take_snapshot(const std::string &snapshot_name) { p->take_snapshot(snapshot_name); }
+void Plater::take_snapshot(const wxString &snapshot_name) { p->take_snapshot(snapshot_name); }
+void Plater::suppress_snapshots() { p->suppress_snapshots(); }
+void Plater::allow_snapshots() { p->allow_snapshots(); }
+void Plater::undo() { p->undo(); }
+void Plater::redo() { p->redo(); }
+void Plater::undo_to(int selection)
+{
+    if (selection == 0) {
+        p->undo();
+        return;
+    }
+    
+    const int idx = p->get_active_snapshot_index() - selection - 1;
+    p->undo_to(p->undo_redo_stack.snapshots()[idx].timestamp);
+}
+void Plater::redo_to(int selection)
+{
+    if (selection == 0) {
+        p->redo();
+        return;
+    }
+    
+    const int idx = p->get_active_snapshot_index() + selection + 1;
+    p->redo_to(p->undo_redo_stack.snapshots()[idx].timestamp);
+}
+bool Plater::undo_redo_string_getter(const bool is_undo, int idx, const char** out_text)
+{
+    const std::vector<UndoRedo::Snapshot>& ss_stack = p->undo_redo_stack.snapshots();
+    const int idx_in_ss_stack = p->get_active_snapshot_index() + (is_undo ? -(++idx) : idx);
+
+    if (0 < idx_in_ss_stack && idx_in_ss_stack < ss_stack.size() - 1) {
+        *out_text = ss_stack[idx_in_ss_stack].name.c_str();
+        return true;
+    }
+
+    return false;
+}
+
 void Plater::on_extruders_change(int num_extruders)
 {
     auto& choices = sidebar().combos_filament();
@@ -4290,8 +4439,11 @@ void Plater::copy_selection_to_clipboard()
 
 void Plater::paste_from_clipboard()
 {
-    if (can_paste_from_clipboard())
-        p->view3D->get_canvas3d()->get_selection().paste_from_clipboard();
+    if (!can_paste_from_clipboard())
+        return;
+
+    this->take_snapshot(_(L("Paste From Clipboard")));
+    p->view3D->get_canvas3d()->get_selection().paste_from_clipboard();
 }
 
 void Plater::msw_rescale()
@@ -4356,6 +4508,16 @@ bool Plater::can_copy_to_clipboard() const
     return true;
 }
 
+bool Plater::can_undo() const
+{
+    return p->undo_redo_stack.has_undo_snapshot();
+}
+
+bool Plater::can_redo() const
+{
+    return p->undo_redo_stack.has_redo_snapshot();
+}
+
 SuppressBackgroundProcessingUpdate::SuppressBackgroundProcessingUpdate() :
     m_was_running(wxGetApp().plater()->is_background_process_running())
 {
diff --git a/src/slic3r/GUI/Plater.hpp b/src/slic3r/GUI/Plater.hpp
index 9ba63461e..e73f88ef3 100644
--- a/src/slic3r/GUI/Plater.hpp
+++ b/src/slic3r/GUI/Plater.hpp
@@ -184,6 +184,16 @@ public:
     void fix_through_netfabb(const int obj_idx, const int vol_idx = -1);
     void send_gcode();
 
+    void take_snapshot(const std::string &snapshot_name);
+    void take_snapshot(const wxString &snapshot_name);
+    void suppress_snapshots();
+    void allow_snapshots();
+    void undo();
+    void redo();
+    void undo_to(int selection);
+    void redo_to(int selection);
+    bool undo_redo_string_getter(const bool is_undo, int idx, const char** out_text);
+
     void on_extruders_change(int extruders_count);
     void on_config_change(const DynamicPrintConfig &config);
     // On activating the parent window.
@@ -218,6 +228,8 @@ public:
     bool can_layers_editing() const;
     bool can_paste_from_clipboard() const;
     bool can_copy_to_clipboard() const;
+    bool can_undo() const;
+    bool can_redo() const;
 
     void msw_rescale();
 
diff --git a/src/slic3r/GUI/PresetBundle.cpp b/src/slic3r/GUI/PresetBundle.cpp
index b28cb2eda..00c1f8168 100644
--- a/src/slic3r/GUI/PresetBundle.cpp
+++ b/src/slic3r/GUI/PresetBundle.cpp
@@ -1366,7 +1366,7 @@ void PresetBundle::export_configbundle(const std::string &path, bool export_syst
                 continue;
             c << std::endl << "[" << presets->section_name() << ":" << preset.name << "]" << std::endl;
             for (const std::string &opt_key : preset.config.keys())
-                c << opt_key << " = " << preset.config.serialize(opt_key) << std::endl;
+                c << opt_key << " = " << preset.config.opt_serialize(opt_key) << std::endl;
         }
     }
 
diff --git a/src/slic3r/GUI/Selection.cpp b/src/slic3r/GUI/Selection.cpp
index 696ba6c1e..b960f8369 100644
--- a/src/slic3r/GUI/Selection.cpp
+++ b/src/slic3r/GUI/Selection.cpp
@@ -312,6 +312,22 @@ void Selection::add_all()
     this->set_bounding_boxes_dirty();
 }
 
+void Selection::set_deserialized(EMode mode, const std::vector<std::pair<size_t, size_t>> &volumes_and_instances)
+{
+    if (! m_valid)
+        return;
+
+	m_mode = mode;
+    for (unsigned int i : m_list)
+        (*m_volumes)[i]->selected = false;
+    m_list.clear();
+    for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++ i)
+		if (std::binary_search(volumes_and_instances.begin(), volumes_and_instances.end(), (*m_volumes)[i]->geometry_id))
+			this->do_add_volume(i);
+    update_type();
+    this->set_bounding_boxes_dirty();
+}
+
 void Selection::clear()
 {
     if (!m_valid)
@@ -790,6 +806,8 @@ void Selection::scale_to_fit_print_volume(const DynamicPrintConfig& config)
             double s = std::min(sx, std::min(sy, sz));
             if (s != 1.0)
             {
+                wxGetApp().plater()->take_snapshot(_(L("Scale To Fit")));
+
                 TransformationType type;
                 type.set_world();
                 type.set_relative();
@@ -798,12 +816,12 @@ void Selection::scale_to_fit_print_volume(const DynamicPrintConfig& config)
                 // apply scale
                 start_dragging();
                 scale(s * Vec3d::Ones(), type);
-                wxGetApp().plater()->canvas3D()->do_scale();
+                wxGetApp().plater()->canvas3D()->do_scale(""); // avoid storing another snapshot
 
                 // center selection on print bed
                 start_dragging();
                 translate(print_volume.center() - get_bounding_box().center());
-                wxGetApp().plater()->canvas3D()->do_move();
+                wxGetApp().plater()->canvas3D()->do_move(""); // avoid storing another snapshot
 
                 wxGetApp().obj_manipul()->set_dirty();
             }
@@ -1177,7 +1195,7 @@ void Selection::copy_to_clipboard()
         ModelObject* dst_object = m_clipboard.add_object();
         dst_object->name                 = src_object->name;
         dst_object->input_file           = src_object->input_file;
-        dst_object->config               = src_object->config;
+		static_cast<DynamicPrintConfig&>(dst_object->config) = static_cast<const DynamicPrintConfig&>(src_object->config);
         dst_object->sla_support_points   = src_object->sla_support_points;
         dst_object->sla_points_status    = src_object->sla_points_status;
         dst_object->layer_config_ranges  = src_object->layer_config_ranges;     // #ys_FIXME_experiment
@@ -2016,6 +2034,10 @@ bool Selection::is_from_fully_selected_instance(unsigned int volume_idx) const
 
 void Selection::paste_volumes_from_clipboard()
 {
+#ifdef _DEBUG
+    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
+
     int dst_obj_idx = get_object_idx();
     if ((dst_obj_idx < 0) || ((int)m_model->objects.size() <= dst_obj_idx))
         return;
@@ -2057,6 +2079,9 @@ void Selection::paste_volumes_from_clipboard()
             }
 
             volumes.push_back(dst_volume);
+#ifdef _DEBUG
+		    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
         }
 
         // keeps relative position of multivolume selections
@@ -2070,10 +2095,18 @@ void Selection::paste_volumes_from_clipboard()
 
         wxGetApp().obj_list()->paste_volumes_into_list(dst_obj_idx, volumes);
     }
+
+#ifdef _DEBUG
+    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
 }
 
 void Selection::paste_objects_from_clipboard()
 {
+#ifdef _DEBUG
+    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
+
     std::vector<size_t> object_idxs;
     const ModelObjectPtrs& src_objects = m_clipboard.get_objects();
     for (const ModelObject* src_object : src_objects)
@@ -2087,9 +2120,16 @@ void Selection::paste_objects_from_clipboard()
         }
 
         object_idxs.push_back(m_model->objects.size() - 1);
+#ifdef _DEBUG
+	    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
     }
 
     wxGetApp().obj_list()->paste_objects_into_list(object_idxs);
+
+#ifdef _DEBUG
+    check_model_ids_validity(*m_model);
+#endif /* _DEBUG */
 }
 
 } // namespace GUI
diff --git a/src/slic3r/GUI/Selection.hpp b/src/slic3r/GUI/Selection.hpp
index 4674a4804..915a8c855 100644
--- a/src/slic3r/GUI/Selection.hpp
+++ b/src/slic3r/GUI/Selection.hpp
@@ -171,7 +171,7 @@ private:
         Vec3d dragging_center;
         // Map from indices of ModelObject instances in Model::objects
         // to a set of indices of ModelVolume instances in ModelObject::instances
-        // Here the index means a position inside the respective std::vector, not ModelID.
+        // Here the index means a position inside the respective std::vector, not ObjectID.
         ObjectIdxsToInstanceIdxsMap content;
     };
 
@@ -237,6 +237,9 @@ public:
 
     void add_all();
 
+    // To be called after Undo or Redo once the volumes are updated.
+    void set_deserialized(EMode mode, const std::vector<std::pair<size_t, size_t>> &volumes_and_instances);
+
     // Update the selection based on the new instance IDs.
 	void instances_changed(const std::vector<size_t> &instance_ids_selected);
     // Update the selection based on the map from old indices to new indices after m_volumes changed.
diff --git a/src/slic3r/Utils/UndoRedo.cpp b/src/slic3r/Utils/UndoRedo.cpp
new file mode 100644
index 000000000..058062502
--- /dev/null
+++ b/src/slic3r/Utils/UndoRedo.cpp
@@ -0,0 +1,821 @@
+#include "UndoRedo.hpp"
+
+#include <algorithm>
+#include <iostream>
+#include <fstream>
+#include <memory>
+#include <typeinfo> 
+#include <cassert>
+#include <cstddef>
+
+#include <cereal/types/polymorphic.hpp>
+#include <cereal/types/map.hpp> 
+#include <cereal/types/string.hpp> 
+#include <cereal/types/utility.hpp> 
+#include <cereal/types/vector.hpp> 
+#include <cereal/archives/binary.hpp>
+#define CEREAL_FUTURE_EXPERIMENTAL
+#include <cereal/archives/adapters.hpp>
+
+#include <libslic3r/ObjectID.hpp>
+
+#include <boost/foreach.hpp>
+
+#ifndef NDEBUG
+// #define SLIC3R_UNDOREDO_DEBUG
+#endif /* NDEBUG */
+
+namespace Slic3r {
+namespace UndoRedo {
+
+static std::string topmost_snapsnot_name = "@@@ Topmost @@@";
+
+bool Snapshot::is_topmost() const
+{
+	return this->name == topmost_snapsnot_name;
+}
+
+// Time interval, start is closed, end is open.
+struct Interval
+{
+public:
+	Interval(size_t begin, size_t end) : m_begin(begin), m_end(end) {}
+
+	size_t  begin() const { return m_begin; }
+	size_t  end()   const { return m_end; }
+
+	bool 	is_valid() const { return m_begin >= 0 && m_begin < m_end; }
+	// This interval comes strictly before the rhs interval.
+	bool 	strictly_before(const Interval &rhs) const { return this->is_valid() && rhs.is_valid() && m_end <= rhs.m_begin; }
+	// This interval comes strictly after the rhs interval.
+	bool 	strictly_after(const Interval &rhs) const { return this->is_valid() && rhs.is_valid() && rhs.m_end <= m_begin; }
+
+	bool    operator<(const Interval &rhs) const { return (m_begin < rhs.m_begin) || (m_begin == rhs.m_begin && m_end < rhs.m_end); }
+	bool 	operator==(const Interval &rhs) const { return m_begin == rhs.m_begin && m_end == rhs.m_end; }
+
+	void    trim_end(size_t new_end) { m_end = std::min(m_end, new_end); }
+	void 	extend_end(size_t new_end) { assert(new_end >= m_end); m_end = new_end; }
+
+private:
+	size_t 	m_begin;
+	size_t 	m_end;
+};
+
+// History of a single object tracked by the Undo / Redo stack. The object may be mutable or immutable.
+class ObjectHistoryBase
+{
+public:
+	virtual ~ObjectHistoryBase() {}
+
+	// Is the object captured by this history mutable or immutable?
+	virtual bool is_mutable() const = 0;
+	virtual bool is_immutable() const = 0;
+	virtual const void* immutable_object_ptr() const { return nullptr; }
+
+	// If the history is empty, the ObjectHistory object could be released.
+	virtual bool empty() = 0;
+
+	// Release all data after the given timestamp. For the ImmutableObjectHistory, the shared pointer is NOT released.
+	virtual void release_after_timestamp(size_t timestamp) = 0;
+
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	// Human readable debug information.
+	virtual std::string	format() = 0;
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+
+#ifndef NDEBUG
+	virtual bool valid() = 0;
+#endif /* NDEBUG */
+};
+
+template<typename T> class ObjectHistory : public ObjectHistoryBase
+{
+public:
+	~ObjectHistory() override {}
+
+	// If the history is empty, the ObjectHistory object could be released.
+	bool empty() override { return m_history.empty(); }
+
+	// Release all data after the given timestamp. The shared pointer is NOT released.
+	void release_after_timestamp(size_t timestamp) override {
+		assert(! m_history.empty());
+		assert(this->valid());
+		// it points to an interval which either starts with timestamp, or follows the timestamp.
+		auto it = std::lower_bound(m_history.begin(), m_history.end(), T(timestamp, timestamp));
+		if (it != m_history.begin()) {
+			auto it_prev = it;
+			-- it_prev;
+			assert(it_prev->begin() < timestamp);
+			// Trim the last interval with timestamp.
+			it_prev->trim_end(timestamp);
+		}
+		m_history.erase(it, m_history.end());
+		assert(this->valid());
+	}
+
+protected:
+	std::vector<T>	m_history;
+};
+
+// Big objects (mainly the triangle meshes) are tracked by Slicer using the shared pointers
+// and they are immutable.
+// The Undo / Redo stack therefore may keep a shared pointer to these immutable objects
+// and as long as the ref counter of these objects is higher than 1 (1 reference is held
+// by the Undo / Redo stack), there is no cost associated to holding the object
+// at the Undo / Redo stack. Once the reference counter drops to 1 (only the Undo / Redo
+// stack holds the reference), the shared pointer may get serialized (and possibly compressed)
+// and the shared pointer may be released.
+// The history of a single immutable object may not be continuous, as an immutable object may
+// be removed from the scene while being kept at the Copy / Paste stack.
+template<typename T>
+class ImmutableObjectHistory : public ObjectHistory<Interval>
+{
+public:
+	ImmutableObjectHistory(std::shared_ptr<const T>	shared_object) : m_shared_object(shared_object) {}
+	~ImmutableObjectHistory() override {}
+
+	bool is_mutable() const override { return false; }
+	bool is_immutable() const override { return true; }
+	const void* immutable_object_ptr() const { return (const void*)m_shared_object.get(); }
+
+	void save(size_t active_snapshot_time, size_t current_time) {
+		assert(m_history.empty() || m_history.back().end() <= active_snapshot_time || 
+			// The snapshot of an immutable object may have already been taken from another mutable object.
+			(m_history.back().begin() <= active_snapshot_time && m_history.back().end() == current_time + 1));
+		if (m_history.empty() || m_history.back().end() < active_snapshot_time)
+			m_history.emplace_back(active_snapshot_time, current_time + 1);
+		else
+			m_history.back().extend_end(current_time + 1);
+	}
+
+	bool has_snapshot(size_t timestamp) {
+		if (m_history.empty())
+			return false;
+		auto it = std::lower_bound(m_history.begin(), m_history.end(), Interval(timestamp, timestamp));
+		if (it == m_history.end() || it->begin() > timestamp) {
+			if (it == m_history.begin())
+				return false;
+			-- it;
+		}
+		return timestamp >= it->begin() && timestamp < it->end();
+	}
+
+	bool 						is_serialized() const { return m_shared_object.get() == nullptr; }
+	const std::string&			serialized_data() const { return m_serialized; }
+	std::shared_ptr<const T>& 	shared_ptr(StackImpl &stack);
+
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::string 				format() override {
+		std::string out = typeid(T).name();
+		out += this->is_serialized() ? 
+			std::string(" len:") + std::to_string(m_serialized.size()) : 
+			std::string(" shared_ptr:") + ptr_to_string(m_shared_object.get());
+		for (const Interval &interval : m_history)
+			out += std::string(", <") + std::to_string(interval.begin()) + "," + std::to_string(interval.end()) + ")";
+		return out;
+	}
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+
+#ifndef NDEBUG
+	bool 						valid() override;
+#endif /* NDEBUG */
+
+private:
+	// Either the source object is held by a shared pointer and the m_serialized field is empty,
+	// or the shared pointer is null and the object is being serialized into m_serialized.
+	std::shared_ptr<const T>	m_shared_object;
+	std::string 				m_serialized;
+};
+
+struct MutableHistoryInterval
+{
+private:
+	struct Data
+	{
+		// Reference counter of this data chunk. We may have used shared_ptr, but the shared_ptr is thread safe
+		// with the associated cost of CPU cache invalidation on refcount change.
+		size_t		refcnt;
+		size_t		size;
+		char 		data[1];
+
+		bool 		matches(const std::string& rhs) { return this->size == rhs.size() && memcmp(this->data, rhs.data(), this->size) == 0; }
+	};
+
+	Interval    m_interval;
+	Data	   *m_data;
+
+public:
+	MutableHistoryInterval(const Interval &interval, const std::string &input_data) : m_interval(interval), m_data(nullptr) {
+		m_data = (Data*)new char[offsetof(Data, data) + input_data.size()];
+		m_data->refcnt = 1;
+		m_data->size = input_data.size();
+		memcpy(m_data->data, input_data.data(), input_data.size());
+	}
+
+	MutableHistoryInterval(const Interval &interval, MutableHistoryInterval &other) : m_interval(interval), m_data(other.m_data) {
+		++ m_data->refcnt;
+	}
+
+	// as a key for std::lower_bound
+	MutableHistoryInterval(const size_t begin, const size_t end) : m_interval(begin, end), m_data(nullptr) {}
+
+	MutableHistoryInterval(MutableHistoryInterval&& rhs) : m_interval(rhs.m_interval), m_data(rhs.m_data) { rhs.m_data = nullptr; }
+	MutableHistoryInterval& operator=(MutableHistoryInterval&& rhs) { m_interval = rhs.m_interval; m_data = rhs.m_data; rhs.m_data = nullptr; return *this; }
+
+	~MutableHistoryInterval() {
+		if (m_data != nullptr && -- m_data->refcnt == 0)
+			delete[] (char*)m_data;
+	}
+
+	const Interval& interval() const { return m_interval; }
+	size_t		begin() const { return m_interval.begin(); }
+	size_t		end()   const { return m_interval.end(); }
+	void 		trim_end(size_t timestamp) { m_interval.trim_end(timestamp); }
+	void 		extend_end(size_t timestamp) { m_interval.extend_end(timestamp); }
+
+	bool		operator<(const MutableHistoryInterval& rhs) const { return m_interval < rhs.m_interval; }
+	bool 		operator==(const MutableHistoryInterval& rhs) const { return m_interval == rhs.m_interval; }
+
+	const char* data() const { return m_data->data; }
+	size_t  	size() const { return m_data->size; }
+	size_t		refcnt() const { return m_data->refcnt; }
+	bool		matches(const std::string& data) { return m_data->matches(data); }
+
+private:
+	MutableHistoryInterval(const MutableHistoryInterval &rhs);
+	MutableHistoryInterval& operator=(const MutableHistoryInterval &rhs);
+};
+
+static inline std::string ptr_to_string(const void* ptr)
+{
+	char buf[64];
+	sprintf(buf, "%p", ptr);
+	return buf;
+}
+
+// Smaller objects (Model, ModelObject, ModelInstance, ModelVolume, DynamicPrintConfig)
+// are mutable and there is not tracking of the changes, therefore a snapshot needs to be
+// taken every time and compared to the previous data at the Undo / Redo stack.
+// The serialized data is stored if it is different from the last value on the stack, otherwise
+// the serialized data is discarded.
+// The history of a single mutable object may not be continuous, as an mutable object may
+// be removed from the scene while being kept at the Copy / Paste stack, therefore an object snapshot
+// with the same serialized object data may be shared by multiple history intervals.
+template<typename T>
+class MutableObjectHistory : public ObjectHistory<MutableHistoryInterval>
+{
+public:
+	~MutableObjectHistory() override {}
+
+	bool is_mutable() const override { return true; }
+	bool is_immutable() const override { return false; }
+
+	void save(size_t active_snapshot_time, size_t current_time, const std::string &data) {
+		assert(m_history.empty() || m_history.back().end() <= active_snapshot_time);
+		if (m_history.empty() || m_history.back().end() < active_snapshot_time) {
+			if (! m_history.empty() && m_history.back().matches(data))
+				// Share the previous data by reference counting.
+				m_history.emplace_back(Interval(current_time, current_time + 1), m_history.back());
+			else
+				// Allocate new data.
+				m_history.emplace_back(Interval(current_time, current_time + 1), data);
+		} else {
+			assert(! m_history.empty());
+			assert(m_history.back().end() == active_snapshot_time);
+			if (m_history.back().matches(data))
+				// Just extend the last interval using the old data.
+				m_history.back().extend_end(current_time + 1);
+			else
+				// Allocate new data time continuous with the previous data.
+				m_history.emplace_back(Interval(active_snapshot_time, current_time + 1), data);
+		}
+	}
+
+	std::string load(size_t timestamp) const {
+		assert(! m_history.empty());
+		auto it = std::lower_bound(m_history.begin(), m_history.end(), MutableHistoryInterval(timestamp, timestamp));
+		if (it == m_history.end() || it->begin() > timestamp) {
+			assert(it != m_history.begin());
+			-- it;
+		}
+		assert(timestamp >= it->begin() && timestamp < it->end());
+		return std::string(it->data(), it->data() + it->size());
+	}
+
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::string format() override {
+		std::string out = typeid(T).name();
+		for (const MutableHistoryInterval &interval : m_history)
+			out += std::string(", ptr:") + ptr_to_string(interval.data()) + " len:" + std::to_string(interval.size()) + " <" + std::to_string(interval.begin()) + "," + std::to_string(interval.end()) + ")";
+		return out;
+	}
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+
+#ifndef NDEBUG
+	bool valid() override;
+#endif /* NDEBUG */
+};
+
+#ifndef NDEBUG
+template<typename T>
+bool ImmutableObjectHistory<T>::valid()
+{
+	// The immutable object content is captured either by a shared object, or by its serialization, but not both.
+	assert(! m_shared_object == ! m_serialized.empty());
+	// Verify that the history intervals are sorted and do not overlap.
+	if (! m_history.empty())
+		for (size_t i = 1; i < m_history.size(); ++ i)
+			assert(m_history[i - 1].strictly_before(m_history[i]));
+	return true;
+}
+#endif /* NDEBUG */
+
+#ifndef NDEBUG
+template<typename T>
+bool MutableObjectHistory<T>::valid()
+{
+	// Verify that the history intervals are sorted and do not overlap, and that the data reference counters are correct.
+	if (! m_history.empty()) {
+		std::map<const char*, size_t> refcntrs;
+		assert(m_history.front().data() != nullptr);
+		++ refcntrs[m_history.front().data()];
+		for (size_t i = 1; i < m_history.size(); ++ i) {
+			assert(m_history[i - 1].interval().strictly_before(m_history[i].interval()));
+			++ refcntrs[m_history[i].data()];
+		}
+		for (const auto &hi : m_history) {
+			assert(hi.data() != nullptr);
+			assert(refcntrs[hi.data()] == hi.refcnt());
+		}
+	}
+	return true;
+}
+#endif /* NDEBUG */
+
+class StackImpl
+{
+public:
+	// Stack needs to be initialized. An empty stack is not valid, there must be a "New Project" status stored at the beginning.
+	StackImpl() : m_active_snapshot_time(0), m_current_time(0) {}
+
+	// The Undo / Redo stack is being initialized with an empty model and an empty selection.
+	// The first snapshot cannot be removed.
+	void initialize(const Slic3r::Model &model, const Slic3r::GUI::Selection &selection);
+
+	// Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
+	void take_snapshot(const std::string &snapshot_name, const Slic3r::Model &model, const Slic3r::GUI::Selection &selection);
+	void load_snapshot(size_t timestamp, Slic3r::Model &model);
+
+	bool has_undo_snapshot() const;
+	bool has_redo_snapshot() const;
+	bool undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, size_t jump_to_time);
+	bool redo(Slic3r::Model &model, size_t jump_to_time);
+
+	// Snapshot history (names with timestamps).
+	const std::vector<Snapshot>& 	snapshots() const { return m_snapshots; }
+	// Timestamp of the active snapshot.
+	size_t 							active_snapshot_time() const { return m_active_snapshot_time; }
+
+	const Selection& selection_deserialized() const { return m_selection; }
+
+//protected:
+	template<typename T, typename T_AS> ObjectID save_mutable_object(const T &object);
+	template<typename T> ObjectID save_immutable_object(std::shared_ptr<const T> &object);
+	template<typename T> T* load_mutable_object(const Slic3r::ObjectID id);
+	template<typename T> std::shared_ptr<const T> load_immutable_object(const Slic3r::ObjectID id);
+	template<typename T, typename T_AS> void load_mutable_object(const Slic3r::ObjectID id, T &target);
+
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::string format() const {
+		std::string out = "Objects\n";
+		for (const std::pair<const ObjectID, std::unique_ptr<ObjectHistoryBase>> &kvp : m_objects)
+			out += std::string("ObjectID:") + std::to_string(kvp.first.id) + " " + kvp.second->format() + "\n";
+		out += "Snapshots\n";
+		for (const Snapshot &snapshot : m_snapshots) {
+			if (snapshot.timestamp == m_active_snapshot_time)
+				out += ">>> ";
+			out += std::string("Name: \"") + snapshot.name + "\", timestamp: " + std::to_string(snapshot.timestamp) + 
+				", Model ID:" + ((snapshot.model_id == 0) ? "Invalid" : std::to_string(snapshot.model_id)) + "\n";
+		}
+		if (m_active_snapshot_time > m_snapshots.back().timestamp)
+			out += ">>>\n";
+		out += "Current time: " + std::to_string(m_current_time) + "\n";
+		return out;
+	}
+	void print() const {
+		std::cout << "Undo / Redo stack" << std::endl;
+		std::cout << this->format() << std::endl;
+	}
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+
+
+#ifndef NDEBUG
+	bool valid() const {
+		assert(! m_snapshots.empty());
+		auto it = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+		assert(it != m_snapshots.begin() && it != m_snapshots.end() && it->timestamp == m_active_snapshot_time);
+		assert(m_active_snapshot_time < m_snapshots.back().timestamp || m_snapshots.back().is_topmost());
+		for (auto it = m_objects.begin(); it != m_objects.end(); ++ it)
+			assert(it->second->valid());
+		return true;
+	}
+#endif /* NDEBUG */
+
+private:
+	template<typename T> ObjectID 	immutable_object_id(const std::shared_ptr<const T> &ptr) { 
+		return this->immutable_object_id_impl((const void*)ptr.get());
+	}
+	ObjectID     					immutable_object_id_impl(const void *ptr) {
+		auto it = m_shared_ptr_to_object_id.find(ptr);
+		if (it == m_shared_ptr_to_object_id.end()) {
+			// Allocate a new temporary ObjectID for this shared pointer.
+			ObjectBase object_with_id;
+			it = m_shared_ptr_to_object_id.insert(it, std::make_pair(ptr, object_with_id.id()));
+		}
+		return it->second;
+	}
+	void 							collect_garbage();
+
+	// Each individual object (Model, ModelObject, ModelInstance, ModelVolume, Selection, TriangleMesh)
+	// is stored with its own history, referenced by the ObjectID. Immutable objects do not provide
+	// their own IDs, therefore there are temporary IDs generated for them and stored to m_shared_ptr_to_object_id.
+	std::map<ObjectID, std::unique_ptr<ObjectHistoryBase>> 	m_objects;
+	std::map<const void*, ObjectID>							m_shared_ptr_to_object_id;
+	// Snapshot history (names with timestamps).
+	std::vector<Snapshot>									m_snapshots;
+	// Timestamp of the active snapshot.
+	size_t 													m_active_snapshot_time;
+	// Logical time counter. m_current_time is being incremented with each snapshot taken.
+	size_t 													m_current_time;
+	// Last selection serialized or deserialized.
+	Selection 												m_selection;
+};
+
+using InputArchive  = cereal::UserDataAdapter<StackImpl, cereal::BinaryInputArchive>;
+using OutputArchive = cereal::UserDataAdapter<StackImpl, cereal::BinaryOutputArchive>;
+
+} // namespace UndoRedo
+
+class Model;
+class ModelObject;
+class ModelVolume;
+class ModelInstance;
+class ModelMaterial;
+class ModelConfig;
+class DynamicPrintConfig;
+class TriangleMesh;
+
+} // namespace Slic3r
+
+namespace cereal
+{
+	// Let cereal know that there are load / save non-member functions declared for ModelObject*, ignore serialization of pointers triggering 
+	// static assert, that cereal does not support serialization of raw pointers.
+	template <class Archive> struct specialize<Archive, Slic3r::Model*, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, Slic3r::ModelObject*, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, Slic3r::ModelVolume*, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, Slic3r::ModelInstance*, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, Slic3r::ModelMaterial*, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, Slic3r::ModelConfig, cereal::specialization::non_member_load_save> {};
+	template <class Archive> struct specialize<Archive, std::shared_ptr<Slic3r::TriangleMesh>, cereal::specialization::non_member_load_save> {};
+
+	// Store ObjectBase derived class onto the Undo / Redo stack as a separate object,
+	// store just the ObjectID to this stream.
+	template <class T> void save(BinaryOutputArchive& ar, T* const& ptr)
+	{
+		ar(cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar).save_mutable_object<T, T>(*ptr));
+	}
+
+	// Load ObjectBase derived class from the Undo / Redo stack as a separate object
+	// based on the ObjectID loaded from this stream.
+	template <class T> void load(BinaryInputArchive& ar, T*& ptr)
+	{
+		Slic3r::UndoRedo::StackImpl& stack = cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar);
+		size_t id;
+		ar(id);
+		ptr = stack.load_mutable_object<T>(Slic3r::ObjectID(id));
+	}
+
+	// Store ObjectBase derived class onto the Undo / Redo stack as a separate object,
+	// store just the ObjectID to this stream.
+	template <class T> void save(BinaryOutputArchive &ar, const std::unique_ptr<T> &ptr)
+	{
+		ar(cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar).save_mutable_object<T>(*ptr.get()));
+	}
+
+	// Load ObjectBase derived class from the Undo / Redo stack as a separate object
+	// based on the ObjectID loaded from this stream.
+	template <class T> void load(BinaryInputArchive &ar, std::unique_ptr<T> &ptr)
+	{
+		Slic3r::UndoRedo::StackImpl& stack = cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar);
+		size_t id;
+		ar(id);
+		ptr.reset(stack.load_mutable_object<T>(Slic3r::ObjectID(id)));
+	}
+
+	// Store ObjectBase derived class onto the Undo / Redo stack as a separate object,
+	// store just the ObjectID to this stream.
+	void save(BinaryOutputArchive& ar, const Slic3r::ModelConfig &cfg)
+	{
+		ar(cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar).save_mutable_object<Slic3r::ModelConfig, Slic3r::DynamicPrintConfig>(cfg));
+	}
+
+	// Load ObjectBase derived class from the Undo / Redo stack as a separate object
+	// based on the ObjectID loaded from this stream.
+	void load(BinaryInputArchive& ar, Slic3r::ModelConfig &cfg)
+	{
+		Slic3r::UndoRedo::StackImpl& stack = cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar);
+		size_t id;
+		ar(id);
+		stack.load_mutable_object<Slic3r::ModelConfig, Slic3r::DynamicPrintConfig>(Slic3r::ObjectID(id), cfg);
+	}
+
+	// Store ObjectBase derived class onto the Undo / Redo stack as a separate object,
+	// store just the ObjectID to this stream.
+	template <class T> void save(BinaryOutputArchive &ar, const std::shared_ptr<const T> &ptr)
+	{
+		ar(cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar).save_immutable_object<T>(const_cast<std::shared_ptr<const T>&>(ptr)));
+	}
+
+	// Load ObjectBase derived class from the Undo / Redo stack as a separate object
+	// based on the ObjectID loaded from this stream.
+	template <class T> void load(BinaryInputArchive &ar, std::shared_ptr<const T> &ptr)
+	{
+		Slic3r::UndoRedo::StackImpl &stack = cereal::get_user_data<Slic3r::UndoRedo::StackImpl>(ar);
+		size_t id;
+		ar(id);
+		ptr = stack.load_immutable_object<T>(Slic3r::ObjectID(id));
+	}
+}
+
+#include <libslic3r/Model.hpp>
+#include <libslic3r/TriangleMesh.hpp>
+#include <slic3r/GUI/Selection.hpp>
+
+namespace Slic3r {
+namespace UndoRedo {
+
+template<typename T> std::shared_ptr<const T>& 	ImmutableObjectHistory<T>::shared_ptr(StackImpl &stack)
+{
+	if (m_shared_object.get() == nullptr && ! this->m_serialized.empty()) {
+		// Deserialize the object.
+		std::istringstream iss(m_serialized);
+		{
+			Slic3r::UndoRedo::InputArchive archive(stack, iss);
+			typedef typename std::remove_const<T>::type Type;
+			std::unique_ptr<Type> mesh(new Type());
+			archive(*mesh.get());
+			m_shared_object = std::move(mesh);
+		}
+	}
+	return m_shared_object;
+}
+
+template<typename T, typename T_AS> ObjectID StackImpl::save_mutable_object(const T &object)
+{
+	// First find or allocate a history stack for the ObjectID of this object instance.
+	auto it_object_history = m_objects.find(object.id());
+	if (it_object_history == m_objects.end())
+		it_object_history = m_objects.insert(it_object_history, std::make_pair(object.id(), std::unique_ptr<MutableObjectHistory<T>>(new MutableObjectHistory<T>())));
+	auto *object_history = static_cast<MutableObjectHistory<T>*>(it_object_history->second.get());
+	// Then serialize the object into a string.
+	std::ostringstream oss;
+	{
+		Slic3r::UndoRedo::OutputArchive archive(*this, oss);
+		archive(static_cast<const T_AS&>(object));
+	}
+	object_history->save(m_active_snapshot_time, m_current_time, oss.str());
+	return object.id();
+}
+
+template<typename T> ObjectID StackImpl::save_immutable_object(std::shared_ptr<const T> &object)
+{
+	// First allocate a temporary ObjectID for this pointer.
+	ObjectID object_id = this->immutable_object_id(object);
+	// and find or allocate a history stack for the ObjectID associated to this shared_ptr.
+	auto it_object_history = m_objects.find(object_id);
+	if (it_object_history == m_objects.end())
+		it_object_history = m_objects.emplace_hint(it_object_history, object_id, std::unique_ptr<ImmutableObjectHistory<T>>(new ImmutableObjectHistory<T>(object)));
+	// Then save the interval.
+	static_cast<ImmutableObjectHistory<T>*>(it_object_history->second.get())->save(m_active_snapshot_time, m_current_time);
+	return object_id;
+}
+
+template<typename T> T* StackImpl::load_mutable_object(const Slic3r::ObjectID id)
+{
+	T *target = new T();
+	this->load_mutable_object<T, T>(id, *target);
+	return target;
+}
+
+template<typename T> std::shared_ptr<const T> StackImpl::load_immutable_object(const Slic3r::ObjectID id)
+{
+	// First find a history stack for the ObjectID of this object instance.
+	auto it_object_history = m_objects.find(id);
+	assert(it_object_history != m_objects.end());
+	auto *object_history = static_cast<ImmutableObjectHistory<T>*>(it_object_history->second.get());
+	assert(object_history->has_snapshot(m_active_snapshot_time));
+	return object_history->shared_ptr(*this);
+}
+
+template<typename T, typename T_AS> void StackImpl::load_mutable_object(const Slic3r::ObjectID id, T &target)
+{
+	// First find a history stack for the ObjectID of this object instance.
+	auto it_object_history = m_objects.find(id);
+	assert(it_object_history != m_objects.end());
+	auto *object_history = static_cast<const MutableObjectHistory<T>*>(it_object_history->second.get());
+	// Then get the data associated with the object history and m_active_snapshot_time.
+	std::istringstream iss(object_history->load(m_active_snapshot_time));
+	Slic3r::UndoRedo::InputArchive archive(*this, iss);
+	target.m_id = id;
+	archive(static_cast<T_AS&>(target));
+}
+
+// Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
+void StackImpl::take_snapshot(const std::string &snapshot_name, const Slic3r::Model &model, const Slic3r::GUI::Selection &selection)
+{
+	// Release old snapshot data.
+	assert(m_active_snapshot_time <= m_current_time);
+	for (auto &kvp : m_objects)
+		kvp.second->release_after_timestamp(m_active_snapshot_time);
+	{
+		auto it = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+		m_snapshots.erase(it, m_snapshots.end());
+	}
+	// Take new snapshots.
+	this->save_mutable_object<Slic3r::Model, Slic3r::Model>(model);
+	m_selection.volumes_and_instances.clear();
+	m_selection.volumes_and_instances.reserve(selection.get_volume_idxs().size());
+	m_selection.mode = selection.get_mode();
+	for (unsigned int volume_idx : selection.get_volume_idxs())
+		m_selection.volumes_and_instances.emplace_back(selection.get_volume(volume_idx)->geometry_id);
+	this->save_mutable_object<Selection, Selection>(m_selection);
+	// Save the snapshot info.
+	m_snapshots.emplace_back(snapshot_name, m_current_time ++, model.id().id);
+	m_active_snapshot_time = m_current_time;
+	// Save snapshot info of the last "current" aka "top most" state, that is only being serialized
+	// if undoing an action. Such a snapshot has an invalid Model ID assigned if it was not taken yet.
+	m_snapshots.emplace_back(topmost_snapsnot_name, m_active_snapshot_time, 0);
+	// Release empty objects from the history.
+	this->collect_garbage();
+	assert(this->valid());
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::cout << "After snapshot" << std::endl;
+	this->print();
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+}
+
+void StackImpl::load_snapshot(size_t timestamp, Slic3r::Model &model)
+{
+	// Find the snapshot by time. It must exist.
+	const auto it_snapshot = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(timestamp));
+	if (it_snapshot == m_snapshots.end() || it_snapshot->timestamp != timestamp)
+		throw std::runtime_error((boost::format("Snapshot with timestamp %1% does not exist") % timestamp).str());
+
+	m_active_snapshot_time = timestamp;
+	model.clear_objects();
+	model.clear_materials();
+	this->load_mutable_object<Slic3r::Model, Slic3r::Model>(ObjectID(it_snapshot->model_id), model);
+	model.update_links_bottom_up_recursive();
+	m_selection.volumes_and_instances.clear();
+	this->load_mutable_object<Selection, Selection>(m_selection.id(), m_selection);
+	// Sort the volumes so that we may use binary search.
+	std::sort(m_selection.volumes_and_instances.begin(), m_selection.volumes_and_instances.end());
+	this->m_active_snapshot_time = timestamp;
+	assert(this->valid());
+}
+
+bool StackImpl::has_undo_snapshot() const
+{ 
+	assert(this->valid());
+	auto it = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+	return -- it != m_snapshots.begin();
+}
+
+bool StackImpl::has_redo_snapshot() const
+{
+	assert(this->valid());
+	auto it = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+	return ++ it != m_snapshots.end();
+}
+
+bool StackImpl::undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, size_t time_to_load)
+{ 
+	assert(this->valid());
+	if (time_to_load == SIZE_MAX) {
+		auto it_current = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+		if (-- it_current == m_snapshots.begin())
+			return false;
+		time_to_load = it_current->timestamp;
+	}
+	assert(time_to_load < m_active_snapshot_time);
+	assert(std::binary_search(m_snapshots.begin(), m_snapshots.end(), Snapshot(time_to_load)));
+	if (m_active_snapshot_time == m_snapshots.back().timestamp && ! m_snapshots.back().is_topmost_captured()) {
+		// The current state is temporary. The current state needs to be captured to be redoable.
+		this->take_snapshot(topmost_snapsnot_name, model, selection);
+		// The line above entered another topmost_snapshot_name.
+		assert(m_snapshots.back().is_topmost());
+		assert(! m_snapshots.back().is_topmost_captured());
+		// Pop it back, it is not needed as there is now a captured topmost state.
+		m_snapshots.pop_back();
+		// current_time was extended, but it should not cause any harm. Resetting it back may complicate the logic unnecessarily.
+		//-- m_current_time;
+		assert(m_snapshots.back().is_topmost());
+		assert(m_snapshots.back().is_topmost_captured());
+	}
+	this->load_snapshot(time_to_load, model);
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::cout << "After undo" << std::endl;
+ 	this->print();
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+	return true;
+}
+
+bool StackImpl::redo(Slic3r::Model &model, size_t time_to_load)
+{ 
+	assert(this->valid());
+	if (time_to_load == SIZE_MAX) {
+		auto it_current = std::lower_bound(m_snapshots.begin(), m_snapshots.end(), Snapshot(m_active_snapshot_time));
+		if (++ it_current == m_snapshots.end())
+			return false;
+		time_to_load = it_current->timestamp;
+	}
+	assert(time_to_load > m_active_snapshot_time);
+	assert(std::binary_search(m_snapshots.begin(), m_snapshots.end(), Snapshot(time_to_load)));
+	this->load_snapshot(time_to_load, model);
+#ifdef SLIC3R_UNDOREDO_DEBUG
+	std::cout << "After redo" << std::endl;
+ 	this->print();
+#endif /* SLIC3R_UNDOREDO_DEBUG */
+	return true;
+}
+
+void StackImpl::collect_garbage()
+{
+	// Purge objects with empty histories.
+	for (auto it = m_objects.begin(); it != m_objects.end();) {
+		if (it->second->empty()) {
+			if (it->second->immutable_object_ptr() != nullptr)
+				// Release the immutable object from the ptr to ObjectID map.
+				m_shared_ptr_to_object_id.erase(it->second->immutable_object_ptr());
+			it = m_objects.erase(it);
+		} else
+			++ it;
+	}
+}
+
+// Wrappers of the private implementation.
+Stack::Stack() : pimpl(new StackImpl()) {}
+Stack::~Stack() {}
+void Stack::take_snapshot(const std::string &snapshot_name, const Slic3r::Model &model, const Slic3r::GUI::Selection &selection) { pimpl->take_snapshot(snapshot_name, model, selection); }
+bool Stack::has_undo_snapshot() const { return pimpl->has_undo_snapshot(); }
+bool Stack::has_redo_snapshot() const { return pimpl->has_redo_snapshot(); }
+bool Stack::undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, size_t time_to_load) { return pimpl->undo(model, selection, time_to_load); }
+bool Stack::redo(Slic3r::Model &model, size_t time_to_load) { return pimpl->redo(model, time_to_load); }
+const Selection& Stack::selection_deserialized() const { return pimpl->selection_deserialized(); }
+
+const std::vector<Snapshot>& Stack::snapshots() const { return pimpl->snapshots(); }
+size_t Stack::active_snapshot_time() const { return pimpl->active_snapshot_time(); }
+
+} // namespace UndoRedo
+} // namespace Slic3r
+
+
+//FIXME we should have unit tests for testing serialization of basic types as DynamicPrintConfig.
+#if 0
+#include "libslic3r/Config.hpp"
+#include "libslic3r/PrintConfig.hpp"
+namespace Slic3r {
+	bool test_dynamic_print_config_serialization() {
+		FullPrintConfig full_print_config;
+		DynamicPrintConfig cfg;
+		cfg.apply(full_print_config, false);
+
+		std::string serialized;
+	   	try {
+			std::ostringstream ss;
+			cereal::BinaryOutputArchive oarchive(ss);
+	        oarchive(cfg);
+			serialized = ss.str();
+	    } catch (std::runtime_error e) {
+	        e.what();
+	    }
+
+	    DynamicPrintConfig cfg2;
+	   	try {
+			std::stringstream ss(serialized);
+			cereal::BinaryInputArchive iarchive(ss);
+	        iarchive(cfg2);
+	    } catch (std::runtime_error e) {
+	        e.what();
+	    }
+
+	    if (cfg == cfg2) {
+	    	printf("Yes!\n");
+			return true;
+	    }
+	    printf("No!\n");
+		return false;
+	}
+} // namespace Slic3r
+#endif
diff --git a/src/slic3r/Utils/UndoRedo.hpp b/src/slic3r/Utils/UndoRedo.hpp
new file mode 100644
index 000000000..f8bfda08c
--- /dev/null
+++ b/src/slic3r/Utils/UndoRedo.hpp
@@ -0,0 +1,94 @@
+#ifndef slic3r_Utils_UndoRedo_hpp_
+#define slic3r_Utils_UndoRedo_hpp_
+
+#include <algorithm>
+#include <memory>
+#include <string>
+#include <vector>
+#include <cassert>
+
+#include <libslic3r/ObjectID.hpp>
+
+namespace Slic3r {
+
+class Model;
+
+namespace GUI {
+	class Selection;
+} // namespace GUI
+
+namespace UndoRedo {
+
+struct Snapshot
+{
+	Snapshot(size_t timestamp) : timestamp(timestamp) {}
+	Snapshot(const std::string &name, size_t timestamp, size_t model_id) : name(name), timestamp(timestamp), model_id(model_id) {}
+	
+	std::string name;
+	size_t 		timestamp;
+	size_t 		model_id;
+
+	bool		operator< (const Snapshot &rhs) const { return this->timestamp < rhs.timestamp; }
+	bool		operator==(const Snapshot &rhs) const { return this->timestamp == rhs.timestamp; }
+
+	// The topmost snapshot represents the current state when going forward.
+	bool 		is_topmost() const;
+	// The topmost snapshot is not being serialized to the Undo / Redo stack until going back in time, 
+	// when the top most state is being serialized, so we can redo back to the top most state.
+	bool 		is_topmost_captured() const { assert(this->is_topmost()); return model_id > 0; }
+};
+
+// Excerpt of Slic3r::GUI::Selection for serialization onto the Undo / Redo stack.
+struct Selection : public Slic3r::ObjectBase {
+	unsigned char							mode;
+	std::vector<std::pair<size_t, size_t>>	volumes_and_instances;
+	template<class Archive> void serialize(Archive &ar) { ar(mode, volumes_and_instances); }
+};
+
+class StackImpl;
+
+class Stack
+{
+public:
+	// Stack needs to be initialized. An empty stack is not valid, there must be a "New Project" status stored at the beginning.
+	// The first "New Project" snapshot shall not be removed.
+	Stack();
+	~Stack();
+
+	// Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
+	void take_snapshot(const std::string &snapshot_name, const Slic3r::Model &model, const Slic3r::GUI::Selection &selection);
+
+	// To be queried to enable / disable the Undo / Redo buttons at the UI.
+	bool has_undo_snapshot() const;
+	bool has_redo_snapshot() const;
+
+	// Roll back the time. If time_to_load is SIZE_MAX, the previous snapshot is activated.
+	// Undoing an action may need to take a snapshot of the current application state, so that redo to the current state is possible.
+	bool undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, size_t time_to_load = SIZE_MAX);
+
+	// Jump forward in time. If time_to_load is SIZE_MAX, the next snapshot is activated.
+	bool redo(Slic3r::Model &model, size_t time_to_load = SIZE_MAX);
+
+	// Snapshot history (names with timestamps).
+	// Each snapshot indicates start of an interval in which this operation is performed.
+	// There is one additional snapshot taken at the very end, which indicates the current unnamed state.
+
+	const std::vector<Snapshot>& snapshots() const;
+	// Timestamp of the active snapshot. One of the snapshots of this->snapshots() shall have Snapshot::timestamp equal to this->active_snapshot_time().
+	// The snapshot time indicates start of an operation, which is finished at the time of the following snapshot, therefore
+	// the active snapshot is the successive snapshot. The same logic applies to the time_to_load parameter of undo() and redo() operations.
+	size_t active_snapshot_time() const;
+
+	// After load_snapshot() / undo() / redo() the selection is deserialized into a list of ObjectIDs, which needs to be converted
+	// into the list of GLVolume pointers once the 3D scene is updated.
+	const Selection& selection_deserialized() const;
+
+private:
+	friend class StackImpl;
+	std::unique_ptr<StackImpl> 	pimpl;
+};
+
+}; // namespace UndoRedo
+}; // namespace Slic3r
+
+#endif /* slic3r_Utils_UndoRedo_hpp_ */
diff --git a/xs/t/15_config.t b/xs/t/15_config.t
index 397f7e479..1f9fc939b 100644
--- a/xs/t/15_config.t
+++ b/xs/t/15_config.t
@@ -9,19 +9,19 @@ use Test::More tests => 147;
 foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintConfig) {
     $config->set('layer_height', 0.3);
     ok abs($config->get('layer_height') - 0.3) < 1e-4, 'set/get float';
-    is $config->serialize('layer_height'), '0.3', 'serialize float';
+    is $config->opt_serialize('layer_height'), '0.3', 'serialize float';
     
     $config->set('perimeters', 2);
     is $config->get('perimeters'), 2, 'set/get int';
-    is $config->serialize('perimeters'), '2', 'serialize int';
+    is $config->opt_serialize('perimeters'), '2', 'serialize int';
     
     $config->set('extrusion_axis', 'A');
     is $config->get('extrusion_axis'), 'A', 'set/get string';
-    is $config->serialize('extrusion_axis'), 'A', 'serialize string';
+    is $config->opt_serialize('extrusion_axis'), 'A', 'serialize string';
     
     $config->set('notes', "foo\nbar");
     is $config->get('notes'), "foo\nbar", 'set/get string with newline';
-    is $config->serialize('notes'), 'foo\nbar', 'serialize string with newline';
+    is $config->opt_serialize('notes'), 'foo\nbar', 'serialize string with newline';
     $config->set_deserialize('notes', 'bar\nbaz');
     is $config->get('notes'), "bar\nbaz", 'deserialize string with newline';
 
@@ -59,7 +59,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
         )
     {    
         $config->set('filament_notes', $test_data->{values});
-        is $config->serialize('filament_notes'), $test_data->{serialized}, 'serialize multi-string value ' . $test_data->{name};
+        is $config->opt_serialize('filament_notes'), $test_data->{serialized}, 'serialize multi-string value ' . $test_data->{name};
         $config->set_deserialize('filament_notes', '');
         is_deeply $config->get('filament_notes'), [], 'deserialize multi-string value - empty ' . $test_data->{name};
         $config->set_deserialize('filament_notes', $test_data->{serialized});
@@ -68,12 +68,12 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
 
     $config->set('first_layer_height', 0.3);
     ok abs($config->get('first_layer_height') - 0.3) < 1e-4, 'set/get absolute floatOrPercent';
-    is $config->serialize('first_layer_height'), '0.3', 'serialize absolute floatOrPercent';
+    is $config->opt_serialize('first_layer_height'), '0.3', 'serialize absolute floatOrPercent';
     
     $config->set('first_layer_height', '50%');
     $config->get_abs_value('first_layer_height');
     ok abs($config->get_abs_value('first_layer_height') - 0.15) < 1e-4, 'set/get relative floatOrPercent';
-    is $config->serialize('first_layer_height'), '50%', 'serialize relative floatOrPercent';
+    is $config->opt_serialize('first_layer_height'), '50%', 'serialize relative floatOrPercent';
     
     # Uh-oh, we have no point option to test at the moment
     #ok $config->set('print_center', [50,80]), 'valid point coordinates';
@@ -86,11 +86,10 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     
     $config->set('use_relative_e_distances', 1);
     is $config->get('use_relative_e_distances'), 1, 'set/get bool';
-    is $config->serialize('use_relative_e_distances'), '1', 'serialize bool';
-    
+    is $config->opt_serialize('use_relative_e_distances'), '1', 'serialize bool';
     $config->set('gcode_flavor', 'teacup');
     is $config->get('gcode_flavor'), 'teacup', 'set/get enum';
-    is $config->serialize('gcode_flavor'), 'teacup', 'serialize enum';
+    is $config->opt_serialize('gcode_flavor'), 'teacup', 'serialize enum';
     $config->set_deserialize('gcode_flavor', 'mach3');
     is $config->get('gcode_flavor'), 'mach3', 'deserialize enum (gcode_flavor)';
     $config->set_deserialize('gcode_flavor', 'machinekit');
@@ -106,7 +105,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     is_deeply [ map $_->pp, @{$config->get('extruder_offset')} ], [[10,20],[30,45]], 'set/get points';
     $config->set('extruder_offset', [Slic3r::Pointf->new(10,20),Slic3r::Pointf->new(30,45)]);
     is_deeply [ map $_->pp, @{$config->get('extruder_offset')} ], [[10,20],[30,45]], 'set/get points';
-    is $config->serialize('extruder_offset'), '10x20,30x45', 'serialize points';
+    is $config->opt_serialize('extruder_offset'), '10x20,30x45', 'serialize points';
     $config->set_deserialize('extruder_offset', '20x10');
     is_deeply [ map $_->pp, @{$config->get('extruder_offset')} ], [[20,10]], 'deserialize points';
     $config->set_deserialize('extruder_offset', '0x0');
@@ -120,7 +119,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     # truncate ->get() to first decimal digit
     $config->set('nozzle_diameter', [0.2,3]);
     is_deeply [ map int($_*10)/10, @{$config->get('nozzle_diameter')} ], [0.2,3], 'set/get floats';
-    is $config->serialize('nozzle_diameter'), '0.2,3', 'serialize floats';
+    is $config->opt_serialize('nozzle_diameter'), '0.2,3', 'serialize floats';
     $config->set_deserialize('nozzle_diameter', '0.1,0.4');
     is_deeply [ map int($_*10)/10, @{$config->get('nozzle_diameter')} ], [0.1,0.4], 'deserialize floats';
     $config->set_deserialize('nozzle_diameter', '3');
@@ -133,7 +132,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     
     $config->set('temperature', [180,210]);
     is_deeply $config->get('temperature'), [180,210], 'set/get ints';
-    is $config->serialize('temperature'), '180,210', 'serialize ints';
+    is $config->opt_serialize('temperature'), '180,210', 'serialize ints';
     $config->set_deserialize('temperature', '195,220');
     is_deeply $config->get('temperature'), [195,220], 'deserialize ints';
     {
@@ -147,7 +146,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     is $config->get_at('wipe', 0), 1, 'get_at bools';
     is $config->get_at('wipe', 1), 0, 'get_at bools';
     is $config->get_at('wipe', 9), 1, 'get_at bools';
-    is $config->serialize('wipe'), '1,0', 'serialize bools';
+    is $config->opt_serialize('wipe'), '1,0', 'serialize bools';
     $config->set_deserialize('wipe', '0,1,1');
     is_deeply $config->get('wipe'), [0,1,1], 'deserialize bools';
     $config->set_deserialize('wipe', '');
@@ -162,7 +161,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     
     $config->set('post_process', ['foo','bar']);
     is_deeply $config->get('post_process'), ['foo','bar'], 'set/get strings';
-    is $config->serialize('post_process'), 'foo;bar', 'serialize strings';
+    is $config->opt_serialize('post_process'), 'foo;bar', 'serialize strings';
     $config->set_deserialize('post_process', 'bar;baz');
     is_deeply $config->get('post_process'), ['bar','baz'], 'deserialize strings';
     {
diff --git a/xs/xsp/Config.xsp b/xs/xsp/Config.xsp
index e193a2321..f5e6ffb05 100644
--- a/xs/xsp/Config.xsp
+++ b/xs/xsp/Config.xsp
@@ -33,7 +33,7 @@
         %code{% RETVAL = ConfigBase__set_deserialize(THIS, opt_key, str); %};
     void set_ifndef(t_config_option_key opt_key, SV* value, bool deserialize = false)
         %code{% ConfigBase__set_ifndef(THIS, opt_key, value, deserialize); %};
-    std::string serialize(t_config_option_key opt_key);
+    std::string opt_serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
         double get_abs_value(t_config_option_key opt_key, double ratio_over);
@@ -95,7 +95,7 @@
         %code{% RETVAL = ConfigBase__set_deserialize(THIS, opt_key, str); %};
     void set_ifndef(t_config_option_key opt_key, SV* value, bool deserialize = false)
         %code{% ConfigBase__set_ifndef(THIS, opt_key, value, deserialize); %};
-    std::string serialize(t_config_option_key opt_key);
+    std::string opt_serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
         double get_abs_value(t_config_option_key opt_key, double ratio_over);