Particles: initial object socket and emitter node support

Object sockets work now, but only the new Object Transforms and the
Particle Mesh Emitter node use it. The emitter does not actually
use the mesh surface yet. Instead, new particles are just emitted around
the origin of the object.

Internally, handles to object data blocks are passed around in the network,
instead of raw object pointers. Using handles has a couple of benefits:
* The caller of the function has control over which handles can be resolved
  and therefore limit access to specific data. The set of data blocks that
  is accessed by a node tree should be known statically. This is necessary
  for a proper integration with the dependency graph.
* When the pointer to an object changes (e.g. after restarting Blender),
  all handles are still valid.
* When an object is deleted, the handle is invalidated without causing crashes.
* The handle is just an integer that can be stored per particle and can be cached easily.

The mapping between handles and their corresponding data blocks is
stored in the Simulation data block.

26 files changed, 633 insertions, 57 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index 1d01436c7e4..4c55488ecd5 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -1343,6 +1343,7 @@ int ntreeTexExecTree(struct bNodeTree *ntree,
 #define FN_NODE_FLOAT_COMPARE 1202
 #define FN_NODE_GROUP_INSTANCE_ID 1203
 #define FN_NODE_COMBINE_STRINGS 1204
+#define FN_NODE_OBJECT_TRANSFORMS 1205
 
 /** \} */
 
diff --git a/source/blender/blenkernel/BKE_persistent_data_handle.hh b/source/blender/blenkernel/BKE_persistent_data_handle.hh
new file mode 100644
index 00000000000..721132560e3
--- /dev/null
+++ b/source/blender/blenkernel/BKE_persistent_data_handle.hh
@@ -0,0 +1,132 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __BKE_PERSISTENT_DATA_HANDLE_H__
+#define __BKE_PERSISTENT_DATA_HANDLE_H__
+
+/** \file
+ * \ingroup bke
+ *
+ * A PersistentDataHandle is a weak reference to some data in a Blender file. The handle itself is
+ * just a number. A PersistentDataHandleMap is used to convert between handles and the actual data.
+ */
+
+#include "BLI_map.hh"
+
+#include "DNA_ID.h"
+
+struct Object;
+
+namespace blender::bke {
+
+class PersistentDataHandleMap;
+
+class PersistentDataHandle {
+ private:
+  /* Negative values indicate that the handle is "empty". */
+  int32_t handle_;
+
+  friend PersistentDataHandleMap;
+
+ protected:
+  PersistentDataHandle(int handle) : handle_(handle)
+  {
+  }
+
+ public:
+  PersistentDataHandle() : handle_(-1)
+  {
+  }
+
+  friend bool operator==(const PersistentDataHandle &a, const PersistentDataHandle &b)
+  {
+    return a.handle_ == b.handle_;
+  }
+
+  friend bool operator!=(const PersistentDataHandle &a, const PersistentDataHandle &b)
+  {
+    return !(a == b);
+  }
+
+  friend std::ostream &operator<<(std::ostream &stream, const PersistentDataHandle &a)
+  {
+    stream << a.handle_;
+    return stream;
+  }
+
+  uint64_t hash() const
+  {
+    return (uint64_t)handle_;
+  }
+};
+
+class PersistentIDHandle : public PersistentDataHandle {
+  friend PersistentDataHandleMap;
+  using PersistentDataHandle::PersistentDataHandle;
+};
+
+class PersistentObjectHandle : public PersistentIDHandle {
+  friend PersistentDataHandleMap;
+  using PersistentIDHandle::PersistentIDHandle;
+};
+
+class PersistentDataHandleMap {
+ private:
+  Map<int32_t, const ID *> id_by_handle_;
+  Map<const ID *, int32_t> handle_by_id_;
+
+ public:
+  void add(int32_t handle, const ID &id)
+  {
+    BLI_assert(handle >= 0);
+    handle_by_id_.add(&id, handle);
+    id_by_handle_.add(handle, &id);
+  }
+
+  PersistentIDHandle lookup(const ID *id) const
+  {
+    const int handle = handle_by_id_.lookup_default(id, -1);
+    return PersistentIDHandle(handle);
+  }
+
+  PersistentObjectHandle lookup(const Object *object) const
+  {
+    const int handle = handle_by_id_.lookup_default((const ID *)object, -1);
+    return PersistentObjectHandle(handle);
+  }
+
+  const ID *lookup(const PersistentIDHandle &handle) const
+  {
+    const ID *id = id_by_handle_.lookup_default(handle.handle_, nullptr);
+    return id;
+  }
+
+  const Object *lookup(const PersistentObjectHandle &handle) const
+  {
+    const ID *id = this->lookup((const PersistentIDHandle &)handle);
+    if (id == nullptr) {
+      return nullptr;
+    }
+    if (GS(id->name) != ID_OB) {
+      return nullptr;
+    }
+    return (const Object *)id;
+  }
+};
+
+}  // namespace blender::bke
+
+#endif /*  __BKE_PERSISTENT_DATA_HANDLE_H__ */
diff --git a/source/blender/blenkernel/CMakeLists.txt b/source/blender/blenkernel/CMakeLists.txt
index 800fa7d18ee..d702da55ea8 100644
--- a/source/blender/blenkernel/CMakeLists.txt
+++ b/source/blender/blenkernel/CMakeLists.txt
@@ -363,6 +363,7 @@ set(SRC
   BKE_packedFile.h
   BKE_paint.h
   BKE_particle.h
+  BKE_persistent_data_handle.hh
   BKE_pbvh.h
   BKE_pointcache.h
   BKE_pointcloud.h
diff --git a/source/blender/blenkernel/intern/node.c b/source/blender/blenkernel/intern/node.c
index 52f0d259058..20d65e52b09 100644
--- a/source/blender/blenkernel/intern/node.c
+++ b/source/blender/blenkernel/intern/node.c
@@ -4345,6 +4345,7 @@ static void registerFunctionNodes(void)
   register_node_type_fn_switch();
   register_node_type_fn_group_instance_id();
   register_node_type_fn_combine_strings();
+  register_node_type_fn_object_transforms();
 }
 
 void init_nodesystem(void)
diff --git a/source/blender/blenkernel/intern/simulation.cc b/source/blender/blenkernel/intern/simulation.cc
index 1ac987d130d..1f11869e21c 100644
--- a/source/blender/blenkernel/intern/simulation.cc
+++ b/source/blender/blenkernel/intern/simulation.cc
@@ -89,6 +89,9 @@ static void simulation_copy_data(Main *bmain, ID *id_dst, const ID *id_src, cons
   }
 
   BLI_listbase_clear(&simulation_dst->states);
+
+  BLI_duplicatelist(&simulation_dst->persistent_data_handles,
+                    &simulation_src->persistent_data_handles);
 }
 
 static void free_simulation_state_head(SimulationState *state)
@@ -169,6 +172,8 @@ static void simulation_free_data(ID *id)
   }
 
   BKE_simulation_state_remove_all(simulation);
+
+  BLI_freelistN(&simulation->persistent_data_handles);
 }
 
 static void simulation_foreach_id(ID *id, LibraryForeachIDData *data)
@@ -178,6 +183,10 @@ static void simulation_foreach_id(ID *id, LibraryForeachIDData *data)
     /* nodetree **are owned by IDs**, treat them as mere sub-data and not real ID! */
     BKE_library_foreach_ID_embedded(data, (ID **)&simulation->nodetree);
   }
+  LISTBASE_FOREACH (
+      PersistentDataHandleItem *, handle_item, &simulation->persistent_data_handles) {
+    BKE_LIB_FOREACHID_PROCESS_ID(data, handle_item->id, IDWALK_CB_USER);
+  }
 }
 
 IDTypeInfo IDType_ID_SIM = {
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 8bfab730313..f443859e62c 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -8675,8 +8675,12 @@ static void direct_link_volume(BlendDataReader *reader, Volume *volume)
 /** \name Read ID: Simulation
  * \{ */
 
-static void lib_link_simulation(BlendLibReader *UNUSED(reader), Simulation *UNUSED(simulation))
+static void lib_link_simulation(BlendLibReader *reader, Simulation *simulation)
 {
+  LISTBASE_FOREACH (
+      PersistentDataHandleItem *, handle_item, &simulation->persistent_data_handles) {
+    BLO_read_id_address(reader, simulation->id.lib, &handle_item->id);
+  }
 }
 
 static void direct_link_simulation(BlendDataReader *reader, Simulation *simulation)
@@ -8697,6 +8701,8 @@ static void direct_link_simulation(BlendDataReader *reader, Simulation *simulati
       };
     }
   }
+
+  BLO_read_list(reader, &simulation->persistent_data_handles);
 }
 
 /** \} */
@@ -11105,6 +11111,10 @@ static void expand_simulation(BlendExpander *expander, Simulation *simulation)
   if (simulation->adt) {
     expand_animdata(expander, simulation->adt);
   }
+  LISTBASE_FOREACH (
+      PersistentDataHandleItem *, handle_item, &simulation->persistent_data_handles) {
+    BLO_expand(expander, handle_item->id);
+  }
 }
 
 /**
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 8b9de3eea24..d33d8032ed1 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -3859,6 +3859,8 @@ static void write_simulation(BlendWriter *writer, Simulation *simulation, const
         }
       }
     }
+
+    BLO_write_struct_list(writer, PersistentDataHandleItem, &simulation->persistent_data_handles);
   }
 }
 
diff --git a/source/blender/functions/FN_multi_function.hh b/source/blender/functions/FN_multi_function.hh
index 77ab2749377..eaddcee7964 100644
--- a/source/blender/functions/FN_multi_function.hh
+++ b/source/blender/functions/FN_multi_function.hh
@@ -98,6 +98,11 @@ class MultiFunction {
     return signature_.function_name;
   }
 
+  bool depends_on_context() const
+  {
+    return signature_.depends_on_context;
+  }
+
   const MFSignature &signature() const
   {
     return signature_;
diff --git a/source/blender/functions/FN_multi_function_context.hh b/source/blender/functions/FN_multi_function_context.hh
index 3a448cc2c6e..8492fd86742 100644
--- a/source/blender/functions/FN_multi_function_context.hh
+++ b/source/blender/functions/FN_multi_function_context.hh
@@ -29,15 +29,39 @@
 
 #include "BLI_utildefines.h"
 
+#include "BLI_map.hh"
+
 namespace blender::fn {
 
+class MFContext;
+
 class MFContextBuilder {
+ private:
+  Map<std::string, const void *> global_contexts_;
+
+  friend MFContext;
+
+ public:
+  template<typename T> void add_global_context(std::string name, const T *context)
+  {
+    global_contexts_.add_new(std::move(name), (const void *)context);
+  }
 };
 
 class MFContext {
+ private:
+  MFContextBuilder &builder_;
+
  public:
-  MFContext(MFContextBuilder &UNUSED(builder))
+  MFContext(MFContextBuilder &builder) : builder_(builder)
+  {
+  }
+
+  template<typename T> const T *get_global_context(StringRef name) const
   {
+    const void *context = builder_.global_contexts_.lookup_default_as(name, nullptr);
+    /* TODO: Implement type checking. */
+    return (const T *)context;
   }
 };
 
diff --git a/source/blender/functions/FN_multi_function_network.hh b/source/blender/functions/FN_multi_function_network.hh
index f6d6c7417e7..20f8fb2ee43 100644
--- a/source/blender/functions/FN_multi_function_network.hh
+++ b/source/blender/functions/FN_multi_function_network.hh
@@ -95,7 +95,7 @@ class MFNode : NonCopyable, NonMovable {
   Span<MFOutputSocket *> outputs();
   Span<const MFOutputSocket *> outputs() const;
 
-  bool all_inputs_have_origin() const;
+  bool has_unlinked_inputs() const;
 
  private:
   void destruct_sockets();
@@ -341,14 +341,14 @@ inline Span<const MFOutputSocket *> MFNode::outputs() const
   return outputs_;
 }
 
-inline bool MFNode::all_inputs_have_origin() const
+inline bool MFNode::has_unlinked_inputs() const
 {
   for (const MFInputSocket *socket : inputs_) {
     if (socket->origin() == nullptr) {
-      return false;
+      return true;
     }
   }
-  return true;
+  return false;
 }
 
 /* --------------------------------------------------------------------
diff --git a/source/blender/functions/FN_multi_function_params.hh b/source/blender/functions/FN_multi_function_params.hh
index 9cce8bb7401..93d7b47af83 100644
--- a/source/blender/functions/FN_multi_function_params.hh
+++ b/source/blender/functions/FN_multi_function_params.hh
@@ -68,6 +68,10 @@ class MFParamsBuilder {
     virtual_array_spans_.append(ref);
   }
 
+  template<typename T> void add_uninitialized_single_output(T *value)
+  {
+    this->add_uninitialized_single_output(GMutableSpan(CPPType::get<T>(), value, 1));
+  }
   void add_uninitialized_single_output(GMutableSpan ref)
   {
     this->assert_current_param_type(MFParamType::ForSingleOutput(ref.type()));
diff --git a/source/blender/functions/FN_multi_function_signature.hh b/source/blender/functions/FN_multi_function_signature.hh
index af5f61fe2ee..26df7c98e4a 100644
--- a/source/blender/functions/FN_multi_function_signature.hh
+++ b/source/blender/functions/FN_multi_function_signature.hh
@@ -36,6 +36,7 @@ struct MFSignature {
   RawVector<std::string> param_names;
   RawVector<MFParamType> param_types;
   RawVector<int> param_data_indices;
+  bool depends_on_context = false;
 
   int data_index(int param_index) const
   {
@@ -157,6 +158,15 @@ class MFSignatureBuilder {
         break;
     }
   }
+
+  /* Context */
+
+  /** This indicates that the function accesses the context. This disables optimizations that
+   * depend on the fact that the function always performes the same operation. */
+  void depends_on_context()
+  {
+    data_.depends_on_context = true;
+  }
 };
 
 }  // namespace blender::fn
diff --git a/source/blender/functions/intern/multi_function_network_evaluation.cc b/source/blender/functions/intern/multi_function_network_evaluation.cc
index a7e1a2f42af..58577e31c42 100644
--- a/source/blender/functions/intern/multi_function_network_evaluation.cc
+++ b/source/blender/functions/intern/multi_function_network_evaluation.cc
@@ -230,7 +230,7 @@ BLI_NOINLINE void MFNetworkEvaluator::evaluate_network_to_compute_outputs(
     }
 
     BLI_assert(node.is_function());
-    BLI_assert(node.all_inputs_have_origin());
+    BLI_assert(!node.has_unlinked_inputs());
     const MFFunctionNode &function_node = node.as_function();
 
     bool all_origins_are_computed = true;
diff --git a/source/blender/functions/intern/multi_function_network_optimization.cc b/source/blender/functions/intern/multi_function_network_optimization.cc
index e76b2f51a15..f1e047f01a1 100644
--- a/source/blender/functions/intern/multi_function_network_optimization.cc
+++ b/source/blender/functions/intern/multi_function_network_optimization.cc
@@ -142,13 +142,24 @@ void dead_node_removal(MFNetwork &network)
  *
  * \{ */
 
+static bool function_node_can_be_constant(MFFunctionNode *node)
+{
+  if (node->has_unlinked_inputs()) {
+    return false;
+  }
+  if (node->function().depends_on_context()) {
+    return false;
+  }
+  return true;
+}
+
 static Vector<MFNode *> find_non_constant_nodes(MFNetwork &network)
 {
   Vector<MFNode *> non_constant_nodes;
   non_constant_nodes.extend(network.dummy_nodes());
 
   for (MFFunctionNode *node : network.function_nodes()) {
-    if (!node->all_inputs_have_origin()) {
+    if (!function_node_can_be_constant(node)) {
       non_constant_nodes.append(node);
     }
   }
@@ -319,17 +330,18 @@ void constant_folding(MFNetwork &network, ResourceCollector &resources)
 
 static uint64_t compute_node_hash(MFFunctionNode &node, RNG *rng, Span<uint64_t> node_hashes)
 {
+  if (node.function().depends_on_context()) {
+    return BLI_rng_get_uint(rng);
+  }
+  if (node.has_unlinked_inputs()) {
+    return BLI_rng_get_uint(rng);
+  }
+
   uint64_t combined_inputs_hash = 394659347u;
   for (MFInputSocket *input_socket : node.inputs()) {
     MFOutputSocket *origin_socket = input_socket->origin();
-    uint64_t input_hash;
-    if (origin_socket == nullptr) {
-      input_hash = BLI_rng_get_uint(rng);
-    }
-    else {
-      input_hash = BLI_ghashutil_combine_hash(node_hashes[origin_socket->node().id()],
-                                              origin_socket->index());
-    }
+    uint64_t input_hash = BLI_ghashutil_combine_hash(node_hashes[origin_socket->node().id()],
+                                                     origin_socket->index());
     combined_inputs_hash = BLI_ghashutil_combine_hash(combined_inputs_hash, input_hash);
   }
 
diff --git a/source/blender/makesdna/DNA_simulation_types.h b/source/blender/makesdna/DNA_simulation_types.h
index c4ff51a107e..f7a7f94da53 100644
--- a/source/blender/makesdna/DNA_simulation_types.h
+++ b/source/blender/makesdna/DNA_simulation_types.h
@@ -37,6 +37,9 @@ typedef struct Simulation {
 
   /** List containing SimulationState objects. */
   struct ListBase states;
+
+  /** List containing PersistentDataHandleItem objects. */
+  struct ListBase persistent_data_handles;
 } Simulation;
 
 typedef struct SimulationState {
@@ -64,6 +67,15 @@ typedef struct ParticleSimulationState {
   struct ListBase ptcaches;
 } ParticleSimulationState;
 
+/** Stores a mapping between an integer handle and a corresponding ID data block. */
+typedef struct PersistentDataHandleItem {
+  struct PersistentDataHandleItem *next;
+  struct PersistentDataHandleItem *prev;
+  struct ID *id;
+  int handle;
+  char _pad[4];
+} PersistentDataHandleItem;
+
 /* Simulation.flag */
 enum {
   SIM_DS_EXPAND = (1 << 0),
diff --git a/source/blender/nodes/CMakeLists.txt b/source/blender/nodes/CMakeLists.txt
index b3cb8163f2a..80720f5206a 100644
--- a/source/blender/nodes/CMakeLists.txt
+++ b/source/blender/nodes/CMakeLists.txt
@@ -135,6 +135,7 @@ set(SRC
   function/nodes/node_fn_combine_strings.cc
   function/nodes/node_fn_float_compare.cc
   function/nodes/node_fn_group_instance_id.cc
+  function/nodes/node_fn_object_transforms.cc
   function/nodes/node_fn_switch.cc
   function/node_function_util.cc
 
diff --git a/source/blender/nodes/NOD_function.h b/source/blender/nodes/NOD_function.h
index 377ae8bfb84..4c05da694f7 100644
--- a/source/blender/nodes/NOD_function.h
+++ b/source/blender/nodes/NOD_function.h
@@ -26,6 +26,7 @@ void register_node_type_fn_float_compare(void);
 void register_node_type_fn_switch(void);
 void register_node_type_fn_group_instance_id(void);
 void register_node_type_fn_combine_strings(void);
+void register_node_type_fn_object_transforms(void);
 
 #ifdef __cplusplus
 }
diff --git a/source/blender/nodes/NOD_node_tree_multi_function.hh b/source/blender/nodes/NOD_node_tree_multi_function.hh
index 79c2b3c7ce8..81b467eca3a 100644
--- a/source/blender/nodes/NOD_node_tree_multi_function.hh
+++ b/source/blender/nodes/NOD_node_tree_multi_function.hh
@@ -288,7 +288,12 @@ class SocketMFNetworkBuilder : public MFNetworkBuilderBase {
    */
   template<typename T> void set_constant_value(T value)
   {
-    const fn::MultiFunction &fn = this->construct_fn<fn::CustomMF_Constant<T>>(std::move(value));
+    this->construct_generator_fn<fn::CustomMF_Constant<T>>(std::move(value));
+  }
+
+  template<typename T, typename... Args> void construct_generator_fn(Args &&... args)
+  {
+    const fn::MultiFunction &fn = this->construct_fn<T>(std::forward<Args>(args)...);
     this->set_generator_fn(fn);
   }
 
diff --git a/source/blender/nodes/NOD_static_types.h b/source/blender/nodes/NOD_static_types.h
index 91aa11566d3..31ce3f81450 100644
--- a/source/blender/nodes/NOD_static_types.h
+++ b/source/blender/nodes/NOD_static_types.h
@@ -276,6 +276,8 @@ DefNode(FunctionNode, FN_NODE_FLOAT_COMPARE, def_float_compare, "FLOAT_COMPARE",
 DefNode(FunctionNode, FN_NODE_SWITCH,        def_fn_switch,     "SWITCH",        Switch,       "Switch", "")
 DefNode(FunctionNode, FN_NODE_GROUP_INSTANCE_ID, 0,             "GROUP_INSTANCE_ID", GroupInstanceID,  "Group Instance ID", "")
 DefNode(FunctionNode, FN_NODE_COMBINE_STRINGS, 0,               "COMBINE_STRINGS", CombineStrings, "Combine Strings", "")
+DefNode(FunctionNode, FN_NODE_OBJECT_TRANSFORMS, 0,             "OBJECT_TRANSFORMS", ObjectTransforms, "Object Transforms", "")
+
 
 
 /* undefine macros */
diff --git a/source/blender/nodes/function/nodes/node_fn_object_transforms.cc b/source/blender/nodes/function/nodes/node_fn_object_transforms.cc
new file mode 100644
index 00000000000..26b25406590
--- /dev/null
+++ b/source/blender/nodes/function/nodes/node_fn_object_transforms.cc
@@ -0,0 +1,88 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include "node_function_util.hh"
+
+#include "BKE_persistent_data_handle.hh"
+
+static bNodeSocketTemplate fn_node_object_transforms_in[] = {
+    {SOCK_OBJECT, N_("Object")},
+    {-1, ""},
+};
+
+static bNodeSocketTemplate fn_node_object_transforms_out[] = {
+    {SOCK_VECTOR, N_("Location")},
+    {-1, ""},
+};
+
+class ObjectTransformsFunction : public blender::fn::MultiFunction {
+ public:
+  ObjectTransformsFunction()
+  {
+    blender::fn::MFSignatureBuilder signature = this->get_builder("Object Transforms");
+    signature.depends_on_context();
+    signature.single_input<blender::bke::PersistentObjectHandle>("Object");
+    signature.single_output<blender::float3>("Location");
+  }
+
+  void call(blender::IndexMask mask,
+            blender::fn::MFParams params,
+            blender::fn::MFContext context) const override
+  {
+    blender::fn::VSpan handles =
+        params.readonly_single_input<blender::bke::PersistentObjectHandle>(0, "Object");
+    blender::MutableSpan locations = params.uninitialized_single_output<blender::float3>(
+        1, "Location");
+
+    const blender::bke::PersistentDataHandleMap *handle_map =
+        context.get_global_context<blender::bke::PersistentDataHandleMap>(
+            "PersistentDataHandleMap");
+    if (handle_map == nullptr) {
+      locations.fill_indices(mask, {0, 0, 0});
+      return;
+    }
+
+    for (int64_t i : mask) {
+      blender::bke::PersistentObjectHandle handle = handles[i];
+      const Object *object = handle_map->lookup(handle);
+      blender::float3 location;
+      if (object == nullptr) {
+        location = {0, 0, 0};
+      }
+      else {
+        location = object->loc;
+      }
+      locations[i] = location;
+    }
+  }
+};
+
+static void fn_node_object_transforms_expand_in_mf_network(
+    blender::nodes::NodeMFNetworkBuilder &builder)
+{
+  static ObjectTransformsFunction fn;
+  builder.set_matching_fn(fn);
+}
+
+void register_node_type_fn_object_transforms()
+{
+  static bNodeType ntype;
+
+  fn_node_type_base(&ntype, FN_NODE_OBJECT_TRANSFORMS, "Object Transforms", 0, 0);
+  node_type_socket_templates(&ntype, fn_node_object_transforms_in, fn_node_object_transforms_out);
+  ntype.expand_in_mf_network = fn_node_object_transforms_expand_in_mf_network;
+  nodeRegisterType(&ntype);
+}
diff --git a/source/blender/nodes/intern/node_socket.cc b/source/blender/nodes/intern/node_socket.cc
index 3a82438a211..49868505d68 100644
--- a/source/blender/nodes/intern/node_socket.cc
+++ b/source/blender/nodes/intern/node_socket.cc
@@ -34,6 +34,7 @@
 
 #include "BKE_lib_id.h"
 #include "BKE_node.h"
+#include "BKE_persistent_data_handle.hh"
 
 #include "RNA_access.h"
 #include "RNA_types.h"
@@ -583,6 +584,59 @@ static bNodeSocketType *make_socket_type_string()
   return socktype;
 }
 
+class ObjectSocketMultiFunction : public blender::fn::MultiFunction {
+ private:
+  const Object *object_;
+
+ public:
+  ObjectSocketMultiFunction(const Object *object) : object_(object)
+  {
+    blender::fn::MFSignatureBuilder signature = this->get_builder("Object Socket");
+    signature.depends_on_context();
+    signature.single_output<blender::bke::PersistentObjectHandle>("Object");
+  }
+
+  void call(blender::IndexMask mask,
+            blender::fn::MFParams params,
+            blender::fn::MFContext context) const override
+  {
+    blender::MutableSpan output =
+        params.uninitialized_single_output<blender::bke::PersistentObjectHandle>(0, "Object");
+
+    /* Try to get a handle map, so that the object can be converted to a handle. */
+    const blender::bke::PersistentDataHandleMap *handle_map =
+        context.get_global_context<blender::bke::PersistentDataHandleMap>(
+            "PersistentDataHandleMap");
+
+    if (handle_map == nullptr) {
+      /* Return empty handles when there is no handle map. */
+      output.fill_indices(mask, blender::bke::PersistentObjectHandle());
+      return;
+    }
+
+    blender::bke::PersistentObjectHandle handle = handle_map->lookup(object_);
+    for (int64_t i : mask) {
+      output[i] = handle;
+    }
+  }
+};
+
+MAKE_CPP_TYPE(PersistentObjectHandle, blender::bke::PersistentObjectHandle);
+
+static bNodeSocketType *make_socket_type_object()
+{
+  bNodeSocketType *socktype = make_standard_socket_type(SOCK_OBJECT, PROP_NONE);
+  socktype->get_mf_data_type = []() {
+    /* Objects are not passed along as raw pointers, but as handles. */
+    return blender::fn::MFDataType::ForSingle<blender::bke::PersistentObjectHandle>();
+  };
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
+    const Object *object = builder.socket_default_value<bNodeSocketValueObject>()->value;
+    builder.construct_generator_fn<ObjectSocketMultiFunction>(object);
+  };
+  return socktype;
+}
+
 void register_standard_node_socket_types(void)
 {
   /* draw callbacks are set in drawnode.c to avoid bad-level calls */
@@ -615,7 +669,7 @@ void register_standard_node_socket_types(void)
 
   nodeRegisterSocketType(make_standard_socket_type(SOCK_SHADER, PROP_NONE));
 
-  nodeRegisterSocketType(make_standard_socket_type(SOCK_OBJECT, PROP_NONE));
+  nodeRegisterSocketType(make_socket_type_object());
 
   nodeRegisterSocketType(make_standard_socket_type(SOCK_IMAGE, PROP_NONE));
 
diff --git a/source/blender/simulation/intern/particle_function.cc b/source/blender/simulation/intern/particle_function.cc
index e0de68d9b29..935ef7983d9 100644
--- a/source/blender/simulation/intern/particle_function.cc
+++ b/source/blender/simulation/intern/particle_function.cc
@@ -50,12 +50,18 @@ ParticleFunction::ParticleFunction(const fn::MultiFunction *global_fn,
 }
 
 ParticleFunctionEvaluator::ParticleFunctionEvaluator(
-    const ParticleFunction &particle_fn, const ParticleChunkContext &particle_chunk_context)
+    const ParticleFunction &particle_fn,
+    const SimulationSolveContext &solve_context,
+    const ParticleChunkContext &particle_chunk_context)
     : particle_fn_(particle_fn),
+      solve_context_(solve_context),
       particle_chunk_context_(particle_chunk_context),
       mask_(particle_chunk_context_.index_mask()),
       outputs_(particle_fn_.output_types_.size(), nullptr)
 {
+  global_context_.add_global_context("PersistentDataHandleMap", &solve_context_.handle_map());
+  per_particle_context_.add_global_context("PersistentDataHandleMap",
+                                           &solve_context_.handle_map());
 }
 
 ParticleFunctionEvaluator::~ParticleFunctionEvaluator()
diff --git a/source/blender/simulation/intern/particle_function.hh b/source/blender/simulation/intern/particle_function.hh
index bbb40efb388..eec4a700383 100644
--- a/source/blender/simulation/intern/particle_function.hh
+++ b/source/blender/simulation/intern/particle_function.hh
@@ -60,6 +60,7 @@ class ParticleFunctionEvaluator {
  private:
   ResourceCollector resources_;
   const ParticleFunction &particle_fn_;
+  const SimulationSolveContext &solve_context_;
   const ParticleChunkContext &particle_chunk_context_;
   IndexMask mask_;
   fn::MFContextBuilder global_context_;
@@ -69,6 +70,7 @@ class ParticleFunctionEvaluator {
 
  public:
   ParticleFunctionEvaluator(const ParticleFunction &particle_fn,
+                            const SimulationSolveContext &solve_context,
                             const ParticleChunkContext &particle_chunk_context);
   ~ParticleFunctionEvaluator();
 
diff --git a/source/blender/simulation/intern/simulation_collect_influences.cc b/source/blender/simulation/intern/simulation_collect_influences.cc
index d4161b06a00..4760063daca 100644
--- a/source/blender/simulation/intern/simulation_collect_influences.cc
+++ b/source/blender/simulation/intern/simulation_collect_influences.cc
@@ -50,31 +50,51 @@ static Span<const nodes::DNode *> get_particle_simulation_nodes(const nodes::Der
   return tree.nodes_by_type("SimulationNodeParticleSimulation");
 }
 
-static std::optional<Array<std::string>> compute_global_string_inputs(
-    nodes::MFNetworkTreeMap &network_map, Span<const fn::MFInputSocket *> sockets)
+/* Returns true on success. */
+static bool compute_global_inputs(nodes::MFNetworkTreeMap &network_map,
+                                  ResourceCollector &resources,
+                                  Span<const fn::MFInputSocket *> sockets,
+                                  MutableSpan<fn::GMutableSpan> r_results)
 {
   int amount = sockets.size();
   if (amount == 0) {
-    return Array<std::string>();
+    return true;
   }
 
   if (network_map.network().have_dummy_or_unlinked_dependencies(sockets)) {
-    return {};
+    return false;
   }
 
   fn::MFNetworkEvaluator network_fn{{}, sockets};
-
   fn::MFParamsBuilder params{network_fn, 1};
-
-  Array<std::string> strings(amount, NoInitialization());
-  for (int i : IndexRange(amount)) {
-    params.add_uninitialized_single_output(
-        fn::GMutableSpan(fn::CPPType::get<std::string>(), strings.data() + i, 1));
+  for (int param_index : network_fn.param_indices()) {
+    fn::MFParamType param_type = network_fn.param_type(param_index);
+    BLI_assert(param_type.category() == fn::MFParamType::Category::SingleOutput); /* For now. */
+    const fn::CPPType &type = param_type.data_type().single_type();
+    void *buffer = resources.linear_allocator().allocate(type.size(), type.alignment());
+    resources.add(buffer, type.destruct_cb(), AT);
+    fn::GMutableSpan span{type, buffer, 1};
+    r_results[param_index] = span;
+    params.add_uninitialized_single_output(span);
   }
-
   fn::MFContextBuilder context;
-  network_fn.call({0}, params, context);
+  network_fn.call(IndexRange(1), params, context);
+  return true;
+}
 
+static std::optional<Array<std::string>> compute_global_string_inputs(
+    nodes::MFNetworkTreeMap &network_map, Span<const fn::MFInputSocket *> sockets)
+{
+  ResourceCollector local_resources;
+  Array<fn::GMutableSpan> computed_values(sockets.size(), NoInitialization());
+  if (!compute_global_inputs(network_map, local_resources, sockets, computed_values)) {
+    return {};
+  }
+
+  Array<std::string> strings(sockets.size());
+  for (int i : sockets.index_range()) {
+    strings[i] = std::move(computed_values[i].typed<std::string>()[0]);
+  }
   return strings;
 }
 
@@ -203,7 +223,8 @@ class ParticleFunctionForce : public ParticleForce {
     IndexMask mask = context.particle_chunk().index_mask();
     MutableSpan<float3> r_combined_force = context.force_dst();
 
-    ParticleFunctionEvaluator evaluator{particle_fn_, context.particle_chunk()};
+    ParticleFunctionEvaluator evaluator{
+        particle_fn_, context.solve_context(), context.particle_chunk()};
     evaluator.compute();
     fn::VSpan<float3> forces = evaluator.get<float3>(0, "Force");
 
@@ -258,44 +279,120 @@ static void collect_forces(nodes::MFNetworkTreeMap &network_map,
 
 class MyBasicEmitter : public ParticleEmitter {
  private:
-  std::string name_;
+  Array<std::string> names_;
+  const fn::MultiFunction &inputs_fn_;
+  uint32_t seed_;
 
  public:
-  MyBasicEmitter(std::string name) : name_(std::move(name))
+  MyBasicEmitter(Array<std::string> names, const fn::MultiFunction &inputs_fn, uint32_t seed)
+      : names_(std::move(names)), inputs_fn_(inputs_fn), seed_(seed)
   {
   }
 
   void emit(ParticleEmitterContext &context) const override
   {
-    ParticleAllocator *allocator = context.try_get_particle_allocator(name_);
-    if (allocator == nullptr) {
+    fn::MFContextBuilder mf_context;
+    mf_context.add_global_context("PersistentDataHandleMap",
+                                  &context.solve_context().handle_map());
+
+    fn::MFParamsBuilder mf_params{inputs_fn_, 1};
+    bke::PersistentObjectHandle object_handle;
+    float rate;
+    mf_params.add_uninitialized_single_output(&object_handle);
+    mf_params.add_uninitialized_single_output(&rate);
+    inputs_fn_.call(IndexRange(1), mf_params, mf_context);
+
+    const Object *object = context.solve_context().handle_map().lookup(object_handle);
+    if (object == nullptr) {
       return;
     }
 
-    fn::MutableAttributesRef attributes = allocator->allocate(10);
-    RandomNumberGenerator rng{(uint32_t)context.simulation_time_interval().start() ^
-                              (uint32_t)DefaultHash<std::string>{}(name_)};
+    Vector<float3> new_positions;
+    Vector<float3> new_velocities;
+    Vector<float> new_birth_times;
+
+    float start_time = context.simulation_time_interval().start();
+    RandomNumberGenerator rng{(*(uint32_t *)&start_time) ^ seed_};
+
+    int amount = rate * 10;
+    for (int i : IndexRange(amount)) {
+      UNUSED_VARS(i);
+      new_positions.append(rng.get_unit_float3() * 0.3 + float3(object->loc));
+      new_velocities.append(rng.get_unit_float3());
+      new_birth_times.append(context.simulation_time_interval().start());
+    }
+
+    for (StringRef name : names_) {
+      ParticleAllocator *allocator = context.try_get_particle_allocator(name);
+      if (allocator == nullptr) {
+        return;
+      }
 
-    MutableSpan<float3> positions = attributes.get<float3>("Position");
-    MutableSpan<float3> velocities = attributes.get<float3>("Velocity");
-    MutableSpan<float> birth_times = attributes.get<float>("Birth Time");
+      fn::MutableAttributesRef attributes = allocator->allocate(amount);
 
-    for (int i : IndexRange(attributes.size())) {
-      positions[i] = rng.get_unit_float3();
-      velocities[i] = rng.get_unit_float3();
-      birth_times[i] = context.simulation_time_interval().start();
+      initialized_copy_n(new_positions.data(), amount, attributes.get<float3>("Position").data());
+      initialized_copy_n(new_velocities.data(), amount, attributes.get<float3>("Velocity").data());
+      initialized_copy_n(
+          new_birth_times.data(), amount, attributes.get<float>("Birth Time").data());
     }
   }
 };
 
+static Vector<const nodes::DNode *> find_linked_particle_simulations(
+    const nodes::DOutputSocket &output_socket)
+{
+  Vector<const nodes::DNode *> simulation_nodes;
+  for (const nodes::DInputSocket *target_socket : output_socket.linked_sockets()) {
+    if (target_socket->node().idname() == "SimulationNodeParticleSimulation") {
+      simulation_nodes.append(&target_socket->node());
+    }
+  }
+  return simulation_nodes;
+}
+
+static ParticleEmitter *create_particle_emitter(const nodes::DNode &dnode,
+                                                ResourceCollector &resources,
+                                                nodes::MFNetworkTreeMap &network_map)
+{
+  Vector<const nodes::DNode *> simulation_dnodes = find_linked_particle_simulations(
+      dnode.output(0));
+  if (simulation_dnodes.size() == 0) {
+    return nullptr;
+  }
+
+  Array<std::string> names{simulation_dnodes.size()};
+  for (int i : simulation_dnodes.index_range()) {
+    names[i] = dnode_to_path(*simulation_dnodes[i]);
+  }
+
+  Array<const fn::MFInputSocket *> input_sockets{dnode.inputs().size()};
+  for (int i : input_sockets.index_range()) {
+    input_sockets[i] = &network_map.lookup_dummy(dnode.input(i));
+  }
+
+  if (network_map.network().have_dummy_or_unlinked_dependencies(input_sockets)) {
+    return nullptr;
+  }
+
+  fn::MultiFunction &inputs_fn = resources.construct<fn::MFNetworkEvaluator>(
+      AT, Span<const fn::MFOutputSocket *>(), input_sockets.as_span());
+
+  uint32_t seed = DefaultHash<std::string>{}(dnode_to_path(dnode));
+  ParticleEmitter &emitter = resources.construct<MyBasicEmitter>(
+      AT, std::move(names), inputs_fn, seed);
+  return &emitter;
+}
+
 static void collect_emitters(nodes::MFNetworkTreeMap &network_map,
                              ResourceCollector &resources,
                              SimulationInfluences &r_influences)
 {
-  for (const nodes::DNode *dnode : get_particle_simulation_nodes(network_map.tree())) {
-    std::string name = dnode_to_path(*dnode);
-    ParticleEmitter &emitter = resources.construct<MyBasicEmitter>(AT, name);
-    r_influences.particle_emitters.append(&emitter);
+  for (const nodes::DNode *dnode :
+       network_map.tree().nodes_by_type("SimulationNodeParticleMeshEmitter")) {
+    ParticleEmitter *emitter = create_particle_emitter(*dnode, resources, network_map);
+    if (emitter != nullptr) {
+      r_influences.particle_emitters.append(emitter);
+    }
   }
 }
 
@@ -316,6 +413,23 @@ static void prepare_particle_attribute_builders(nodes::MFNetworkTreeMap &network
   }
 }
 
+static void find_used_data_blocks(const nodes::DerivedNodeTree &tree,
+                                  SimulationInfluences &r_influences)
+{
+  const bNodeSocketType *socktype = nodeSocketTypeFind("NodeSocketObject");
+  BLI_assert(socktype != nullptr);
+
+  for (const nodes::DInputSocket *dsocket : tree.input_sockets()) {
+    const bNodeSocket *bsocket = dsocket->bsocket();
+    if (bsocket->typeinfo == socktype) {
+      Object *value = ((const bNodeSocketValueObject *)bsocket->default_value)->value;
+      if (value != nullptr) {
+        r_influences.used_data_blocks.add(&value->id);
+      }
+    }
+  }
+}
+
 void collect_simulation_influences(Simulation &simulation,
                                    ResourceCollector &resources,
                                    SimulationInfluences &r_influences,
@@ -343,6 +457,8 @@ void collect_simulation_influences(Simulation &simulation,
   for (const nodes::DNode *dnode : get_particle_simulation_nodes(tree)) {
     r_states_info.particle_simulation_names.add(dnode_to_path(*dnode));
   }
+
+  find_used_data_blocks(tree, r_influences);
 }
 
 }  // namespace blender::sim
diff --git a/source/blender/simulation/intern/simulation_solver.cc b/source/blender/simulation/intern/simulation_solver.cc
index f542d6ab2c8..158c50957df 100644
--- a/source/blender/simulation/intern/simulation_solver.cc
+++ b/source/blender/simulation/intern/simulation_solver.cc
@@ -17,8 +17,11 @@
 #include "simulation_solver.hh"
 
 #include "BKE_customdata.h"
+#include "BKE_lib_id.h"
+#include "BKE_persistent_data_handle.hh"
 
 #include "BLI_rand.hh"
+#include "BLI_set.hh"
 
 namespace blender::sim {
 
@@ -243,6 +246,53 @@ BLI_NOINLINE static void remove_dead_and_add_new_particles(ParticleSimulationSta
   state.next_particle_id += allocator.total_allocated();
 }
 
+static void update_persistent_data_handles(Simulation &simulation,
+                                           const VectorSet<ID *> &used_data_blocks)
+{
+  Set<ID *> contained_ids;
+  Set<int> used_handles;
+
+  /* Remove handles that have been invalidated. */
+  LISTBASE_FOREACH_MUTABLE (
+      PersistentDataHandleItem *, handle_item, &simulation.persistent_data_handles) {
+    if (handle_item->id == nullptr) {
+      BLI_remlink(&simulation.persistent_data_handles, handle_item);
+      continue;
+    }
+    if (!used_data_blocks.contains(handle_item->id)) {
+      id_us_min(handle_item->id);
+      BLI_remlink(&simulation.persistent_data_handles, handle_item);
+      MEM_freeN(handle_item);
+      continue;
+    }
+    contained_ids.add_new(handle_item->id);
+    used_handles.add_new(handle_item->handle);
+  }
+
+  /* Add new handles that are not in the list yet. */
+  int next_handle = 0;
+  for (ID *id : used_data_blocks) {
+    if (contained_ids.contains(id)) {
+      continue;
+    }
+
+    /* Find the next available handle. */
+    while (used_handles.contains(next_handle)) {
+      next_handle++;
+    }
+    used_handles.add_new(next_handle);
+
+    PersistentDataHandleItem *handle_item = (PersistentDataHandleItem *)MEM_callocN(
+        sizeof(*handle_item), AT);
+    /* Cannot store const pointers in DNA. */
+    id_us_plus(id);
+    handle_item->id = id;
+    handle_item->handle = next_handle;
+
+    BLI_addtail(&simulation.persistent_data_handles, handle_item);
+  }
+}
+
 void initialize_simulation_states(Simulation &simulation,
                                   Depsgraph &UNUSED(depsgraph),
                                   const SimulationInfluences &UNUSED(influences))
@@ -255,11 +305,18 @@ void solve_simulation_time_step(Simulation &simulation,
                                 const SimulationInfluences &influences,
                                 float time_step)
 {
-  SimulationSolveContext solve_context{
-      simulation,
-      depsgraph,
-      influences,
-      TimeInterval(simulation.current_simulation_time, time_step)};
+  update_persistent_data_handles(simulation, influences.used_data_blocks);
+
+  bke::PersistentDataHandleMap handle_map;
+  LISTBASE_FOREACH (PersistentDataHandleItem *, handle, &simulation.persistent_data_handles) {
+    handle_map.add(handle->handle, *handle->id);
+  }
+
+  SimulationSolveContext solve_context{simulation,
+                                       depsgraph,
+                                       influences,
+                                       TimeInterval(simulation.current_simulation_time, time_step),
+                                       handle_map};
   TimeInterval simulation_time_interval{simulation.current_simulation_time, time_step};
 
   Vector<SimulationState *> simulation_states{simulation.states};
diff --git a/source/blender/simulation/intern/simulation_solver.hh b/source/blender/simulation/intern/simulation_solver.hh
index b5e42b53846..1d1b9935661 100644
--- a/source/blender/simulation/intern/simulation_solver.hh
+++ b/source/blender/simulation/intern/simulation_solver.hh
@@ -24,6 +24,8 @@
 
 #include "FN_attributes_ref.hh"
 
+#include "BKE_persistent_data_handle.hh"
+
 #include "particle_allocator.hh"
 #include "time_interval.hh"
 
@@ -50,6 +52,7 @@ struct SimulationInfluences {
   Map<std::string, Vector<const ParticleForce *>> particle_forces;
   Map<std::string, fn::AttributesInfoBuilder *> particle_attributes_builder;
   Vector<const ParticleEmitter *> particle_emitters;
+  VectorSet<ID *> used_data_blocks;
 };
 
 class SimulationSolveContext {
@@ -58,16 +61,19 @@ class SimulationSolveContext {
   Depsgraph &depsgraph_;
   const SimulationInfluences &influences_;
   TimeInterval solve_interval_;
+  const bke::PersistentDataHandleMap &id_handle_map_;
 
  public:
   SimulationSolveContext(Simulation &simulation,
                          Depsgraph &depsgraph,
                          const SimulationInfluences &influences,
-                         TimeInterval solve_interval)
+                         TimeInterval solve_interval,
+                         const bke::PersistentDataHandleMap &handle_map)
       : simulation_(simulation),
         depsgraph_(depsgraph),
         influences_(influences),
-        solve_interval_(solve_interval)
+        solve_interval_(solve_interval),
+        id_handle_map_(handle_map)
   {
   }
 
@@ -80,6 +86,11 @@ class SimulationSolveContext {
   {
     return influences_;
   }
+
+  const bke::PersistentDataHandleMap &handle_map() const
+  {
+    return id_handle_map_;
+  }
 };
 
 class ParticleAllocators {
@@ -147,6 +158,11 @@ class ParticleEmitterContext {
   {
   }
 
+  SimulationSolveContext &solve_context()
+  {
+    return solve_context_;
+  }
+
   ParticleAllocator *try_get_particle_allocator(StringRef particle_simulation_name)
   {
     return particle_allocators_.try_get_allocator(particle_simulation_name);
@@ -174,6 +190,11 @@ class ParticleForceContext {
   {
   }
 
+  SimulationSolveContext &solve_context()
+  {
+    return solve_context_;
+  }
+
   const ParticleChunkContext &particle_chunk() const
   {
     return particle_chunk_context_;