WIP: Integration of MMU painting into the slicing back-end.

6 files changed, 191 insertions, 95 deletions

diff --git a/src/libslic3r/ClipperUtils.cpp b/src/libslic3r/ClipperUtils.cpp
index a49665ae5..7216c7509 100644
--- a/src/libslic3r/ClipperUtils.cpp
+++ b/src/libslic3r/ClipperUtils.cpp
@@ -461,6 +461,8 @@ static inline Polygons _clipper(ClipperLib::ClipType clipType, TSubj &&subject,
 
 Slic3r::Polygons diff(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset)
     { return _clipper(ClipperLib::ctDifference, ClipperUtils::PolygonsProvider(subject), ClipperUtils::PolygonsProvider(clip), do_safety_offset); }
+Slic3r::Polygons diff(const Slic3r::Polygons &subject, const Slic3r::ExPolygons &clip, ApplySafetyOffset do_safety_offset)
+    { return _clipper(ClipperLib::ctDifference, ClipperUtils::PolygonsProvider(subject), ClipperUtils::ExPolygonsProvider(clip), do_safety_offset); }
 Slic3r::Polygons diff(const Slic3r::ExPolygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset)
     { return _clipper(ClipperLib::ctDifference, ClipperUtils::ExPolygonsProvider(subject), ClipperUtils::PolygonsProvider(clip), do_safety_offset); }
 Slic3r::Polygons diff(const Slic3r::ExPolygons &subject, const Slic3r::ExPolygons &clip, ApplySafetyOffset do_safety_offset)
diff --git a/src/libslic3r/ClipperUtils.hpp b/src/libslic3r/ClipperUtils.hpp
index fc9677d8b..061658086 100644
--- a/src/libslic3r/ClipperUtils.hpp
+++ b/src/libslic3r/ClipperUtils.hpp
@@ -296,6 +296,7 @@ Slic3r::Lines _clipper_ln(ClipperLib::ClipType clipType, const Slic3r::Lines &su
 
 // Safety offset is applied to the clipping polygons only.
 Slic3r::Polygons   diff(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
+Slic3r::Polygons   diff(const Slic3r::Polygons &subject, const Slic3r::ExPolygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
 Slic3r::Polygons   diff(const Slic3r::ExPolygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
 Slic3r::Polygons   diff(const Slic3r::ExPolygons &subject, const Slic3r::ExPolygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
 Slic3r::ExPolygons diff_ex(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 018754bc0..e68eb7b6d 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -561,7 +561,7 @@ ModelObject& ModelObject::assign_copy(const ModelObject &rhs)
     this->sla_support_points          = rhs.sla_support_points;
     this->sla_points_status           = rhs.sla_points_status;
     this->sla_drain_holes             = rhs.sla_drain_holes;
-    this->layer_config_ranges         = rhs.layer_config_ranges;    // #ys_FIXME_experiment
+    this->layer_config_ranges         = rhs.layer_config_ranges;
     this->layer_height_profile        = rhs.layer_height_profile;
     this->printable                   = rhs.printable;
     this->origin_translation          = rhs.origin_translation;
@@ -602,7 +602,7 @@ ModelObject& ModelObject::assign_copy(ModelObject &&rhs)
     this->sla_support_points          = std::move(rhs.sla_support_points);
     this->sla_points_status           = std::move(rhs.sla_points_status);
     this->sla_drain_holes             = std::move(rhs.sla_drain_holes);
-    this->layer_config_ranges         = std::move(rhs.layer_config_ranges); // #ys_FIXME_experiment
+    this->layer_config_ranges         = std::move(rhs.layer_config_ranges);
     this->layer_height_profile        = std::move(rhs.layer_height_profile);
     this->origin_translation          = std::move(rhs.origin_translation);
     m_bounding_box                    = std::move(rhs.m_bounding_box);
diff --git a/src/libslic3r/PrintApply.cpp b/src/libslic3r/PrintApply.cpp
index 6b6b94f7d..46af1fee8 100644
--- a/src/libslic3r/PrintApply.cpp
+++ b/src/libslic3r/PrintApply.cpp
@@ -645,31 +645,28 @@ bool verify_update_print_object_regions(
             }
 
     // Verify and / or update PrintRegions produced by color painting. 
-    for (const PrintObjectRegions::LayerRangeRegions &layer_range : print_object_regions.layer_ranges) {
-        size_t painted_region_idx = 0;
-        for (unsigned int painted_extruder_id : painting_extruders)
-            for (int parent_region_id = 0; parent_region_id < int(layer_range.volume_regions.size()); ++ parent_region_id) {
-                const PrintObjectRegions::VolumeRegion  &parent_region  = layer_range.volume_regions[parent_region_id];
-                const PrintObjectRegions::PaintedRegion &region         = layer_range.painted_regions[painted_region_idx ++];
-                PrintRegionConfig cfg = parent_region.region->config();
-                cfg.perimeter_extruder.value = painted_extruder_id;
-                cfg.infill_extruder.value    = painted_extruder_id;
-                if (cfg != region.region->config()) {
-                    // Region configuration changed.
-                    if (print_region_ref_cnt(*region.region) == 0) {
-                        // Region is referenced for the first time. Just change its parameters.
-                        // Stop the background process before assigning new configuration to the regions.
-                        t_config_option_keys diff = region.region->config().diff(cfg);
-                        callback_invalidate(region.region->config(), cfg, diff);
-                        region.region->config_apply_only(cfg, diff, false);
-                    } else {
-                        // Region is referenced multiple times, thus the region is being split. We need to reslice.
-                        return false;
-                    }
+    for (const PrintObjectRegions::LayerRangeRegions &layer_range : print_object_regions.layer_ranges)
+        for (const PrintObjectRegions::PaintedRegion &region : layer_range.painted_regions) {
+            const PrintObjectRegions::VolumeRegion &parent_region   = layer_range.volume_regions[region.parent];
+            PrintRegionConfig                       cfg             = parent_region.region->config();
+            cfg.perimeter_extruder.value    = region.extruder_id;
+            cfg.solid_infill_extruder.value = region.extruder_id;
+            cfg.infill_extruder.value       = region.extruder_id;
+            if (cfg != region.region->config()) {
+                // Region configuration changed.
+                if (print_region_ref_cnt(*region.region) == 0) {
+                    // Region is referenced for the first time. Just change its parameters.
+                    // Stop the background process before assigning new configuration to the regions.
+                    t_config_option_keys diff = region.region->config().diff(cfg);
+                    callback_invalidate(region.region->config(), cfg, diff);
+                    region.region->config_apply_only(cfg, diff, false);
+                } else {
+                    // Region is referenced multiple times, thus the region is being split. We need to reslice.
+                    return false;
                 }
-                print_region_ref_inc(*region.region);
             }
-    }
+            print_region_ref_inc(*region.region);
+        }
 
     // Lastly verify, whether some regions were not merged.
     {
@@ -855,16 +852,23 @@ static PrintObjectRegions* generate_print_object_regions(
     }
 
     // Finally add painting regions.
-    for (PrintObjectRegions::LayerRangeRegions &layer_range : layer_ranges_regions)
+    for (PrintObjectRegions::LayerRangeRegions &layer_range : layer_ranges_regions) {
         for (unsigned int painted_extruder_id : painting_extruders)
             for (int parent_region_id = 0; parent_region_id < int(layer_range.volume_regions.size()); ++ parent_region_id)
                 if (const PrintObjectRegions::VolumeRegion &parent_region = layer_range.volume_regions[parent_region_id];
                     parent_region.model_volume->is_model_part() || parent_region.model_volume->is_modifier()) {
                     PrintRegionConfig cfg = parent_region.region->config();
-                    cfg.perimeter_extruder.value = painted_extruder_id;
-                    cfg.infill_extruder.value    = painted_extruder_id;
+                    cfg.perimeter_extruder.value    = painted_extruder_id;
+                    cfg.solid_infill_extruder.value = painted_extruder_id;
+                    cfg.infill_extruder.value       = painted_extruder_id;
                     layer_range.painted_regions.push_back({ painted_extruder_id, parent_region_id, get_create_region(std::move(cfg))});
                 }
+        // Sort the regions by parent region::print_object_region_id() and extruder_id to help the slicing algorithm when applying MMU segmentation.
+        std::sort(layer_range.painted_regions.begin(), layer_range.painted_regions.end(), [&layer_range](auto &l, auto &r) {
+            int lid = layer_range.volume_regions[l.parent].region->print_object_region_id();
+            int rid = layer_range.volume_regions[r.parent].region->print_object_region_id();
+            return lid < rid || (lid == rid && l.extruder_id < r.extruder_id); });
+    }
 
     return out.release();
 }
@@ -1049,6 +1053,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
         bool solid_or_modifier_differ   = model_volume_list_changed(model_object, model_object_new, solid_or_modifier_types);
         bool supports_differ            = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::SUPPORT_BLOCKER) ||
                                           model_volume_list_changed(model_object, model_object_new, ModelVolumeType::SUPPORT_ENFORCER);
+        bool mmu_segmentation_differ    = model_mmu_segmentation_data_changed(model_object, model_object_new);
         bool layer_height_ranges_differ = ! layer_height_ranges_equal(model_object.layer_config_ranges, model_object_new.layer_config_ranges, model_object_new.layer_height_profile.empty());
         bool model_origin_translation_differ = model_object.origin_translation != model_object_new.origin_translation;
         auto print_objects_range        = print_object_status_db.get_range(model_object);
@@ -1056,7 +1061,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
         // All PrintObjects in print_objects_range shall point to the same prints_objects_regions
         model_object_status.print_object_regions = print_objects_range.begin()->print_object->m_shared_regions;
         model_object_status.print_object_regions->ref_cnt_inc();
-        if (solid_or_modifier_differ || model_origin_translation_differ || layer_height_ranges_differ ||
+        if (solid_or_modifier_differ || mmu_segmentation_differ || model_origin_translation_differ || layer_height_ranges_differ ||
             ! model_object.layer_height_profile.timestamp_matches(model_object_new.layer_height_profile)) {
             // The very first step (the slicing step) is invalidated. One may freely remove all associated PrintObjects.
             model_object_status.print_object_regions_status = model_origin_translation_differ || layer_height_ranges_differ ?
@@ -1075,7 +1080,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
                 model_object_status.print_object_regions->clear();
             // Copy content of the ModelObject including its ID, do not change the parent.
             model_object.assign_copy(model_object_new);
-        } else { 
+        } else {
             model_object_status.print_object_regions_status = ModelObjectStatus::PrintObjectRegionsStatus::Valid;
             if (supports_differ || model_custom_supports_data_changed(model_object, model_object_new)) {
                 // First stop background processing before shuffling or deleting the ModelVolumes in the ModelObject's list.
@@ -1229,7 +1234,6 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     // All regions now have distinct settings.
     // Check whether applying the new region config defaults we would get different regions,
     // update regions or create regions from scratch.
-    const std::vector<unsigned int> painting_extruders;
     for (auto it_print_object = m_objects.begin(); it_print_object != m_objects.end();) {
         // Find the range of PrintObjects sharing the same associated ModelObject.
         auto                it_print_object_end  = it_print_object;
@@ -1244,6 +1248,13 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
             model_object_status.print_object_regions = print_object_regions;
             print_object_regions->ref_cnt_inc();
         }
+        std::vector<unsigned int> painting_extruders;
+        if (const auto &volumes = print_object.model_object()->volumes; 
+            std::find_if(volumes.begin(), volumes.end(), [](const ModelVolume *v) { return ! v->mmu_segmentation_facets.empty(); }) != volumes.end()) {
+            //FIXME be more specific! Don't enumerate extruders that are not used for painting!
+            painting_extruders.assign(num_extruders, 0);
+            std::iota(painting_extruders.begin(), painting_extruders.end(), 1);
+        }
         if (model_object_status.print_object_regions_status == ModelObjectStatus::PrintObjectRegionsStatus::Valid) {
             // Verify that the trafo for regions & volume bounding boxes thus for regions is still applicable.
             if (print_object_regions && ! trafos_differ_in_rotation_by_z_and_mirroring_by_xy_only(print_object_regions->trafo_bboxes, model_object_status.print_instances.front().trafo))
diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index df635a249..e69edd051 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -6,7 +6,6 @@
 #include "Geometry.hpp"
 #include "I18N.hpp"
 #include "Layer.hpp"
-#include "MultiMaterialSegmentation.hpp"
 #include "SupportMaterial.hpp"
 #include "Surface.hpp"
 #include "Slicing.hpp"
diff --git a/src/libslic3r/PrintObjectSlice.cpp b/src/libslic3r/PrintObjectSlice.cpp
index a64cedd03..f44d6fdbf 100644
--- a/src/libslic3r/PrintObjectSlice.cpp
+++ b/src/libslic3r/PrintObjectSlice.cpp
@@ -1,6 +1,7 @@
 #include "ElephantFootCompensation.hpp"
 #include "I18N.hpp"
 #include "Layer.hpp"
+#include "MultiMaterialSegmentation.hpp"
 #include "Print.hpp"
 
 #include <boost/log/trivial.hpp>
@@ -221,10 +222,34 @@ static inline VolumeSlices& volume_slices_find_by_id(std::vector<VolumeSlices> &
 
 static inline bool overlap_in_xy(const BoundingBoxf3 &l, const BoundingBoxf3 &r)
 {
+    assert(l.defined && r.defined);
     return ! (l.max.x() < r.min.x() || l.min.x() > r.max.x() ||
               l.max.y() < r.min.y() || l.min.y() > r.max.y());
 }
 
+static std::vector<PrintObjectRegions::LayerRangeRegions>::const_iterator layer_range_first(const std::vector<PrintObjectRegions::LayerRangeRegions> &layer_ranges, double z)
+{
+    auto  it = lower_bound_by_predicate(layer_ranges.begin(), layer_ranges.end(),
+        [z](const PrintObjectRegions::LayerRangeRegions &lr) { return lr.layer_height_range.second < z; });
+    assert(it != layer_ranges.end() && it->layer_height_range.first <= z && z <= it->layer_height_range.second);
+    if (z == it->layer_height_range.second)
+        if (auto it_next = it; ++ it_next != layer_ranges.end() && it_next->layer_height_range.first == z)
+            it = it_next;
+    assert(it != layer_ranges.end() && it->layer_height_range.first <= z && z <= it->layer_height_range.second);
+    return it;
+}
+
+static std::vector<PrintObjectRegions::LayerRangeRegions>::const_iterator layer_range_next(
+    const std::vector<PrintObjectRegions::LayerRangeRegions>            &layer_ranges, 
+    std::vector<PrintObjectRegions::LayerRangeRegions>::const_iterator   it,
+    double                                                               z)
+{
+    for (; it->layer_height_range.second <= z; ++ it)
+        assert(it != layer_ranges.end());
+    assert(it != layer_ranges.end() && it->layer_height_range.first <= z && z < it->layer_height_range.second);
+    return it;
+}
+
 static std::vector<std::vector<ExPolygons>> slices_to_regions(
     ModelVolumePtrs                                           model_volumes,
     const PrintObjectRegions                                 &print_object_regions,
@@ -304,13 +329,7 @@ static std::vector<std::vector<ExPolygons>> slices_to_regions(
             [&slices_by_region, &print_object_regions, &zs_complex, &layer_ranges_regions_to_slices, clip_multipart_objects, &throw_on_cancel_callback]
                 (const tbb::blocked_range<size_t> &range) {
                 float z              = zs_complex[range.begin()].second;
-                auto  it_layer_range = lower_bound_by_predicate(print_object_regions.layer_ranges.begin(), print_object_regions.layer_ranges.end(), 
-                    [z](const PrintObjectRegions::LayerRangeRegions &lr){ return lr.layer_height_range.second < z; });
-                assert(it_layer_range != print_object_regions.layer_ranges.end() && it_layer_range->layer_height_range.first <= z && z <= it_layer_range->layer_height_range.second);
-                if (z == it_layer_range->layer_height_range.second)
-                    if (auto it_next = it_layer_range; ++ it_next != print_object_regions.layer_ranges.end() && it_next->layer_height_range.first == z)
-                        it_layer_range = it_next;
-                assert(it_layer_range != print_object_regions.layer_ranges.end() && it_layer_range->layer_height_range.first <= z && z <= it_layer_range->layer_height_range.second);
+                auto  it_layer_range = layer_range_first(print_object_regions.layer_ranges, z);
                 // Per volume_regions slices at this Z height.
                 struct RegionSlice { 
                     ExPolygons  expolygons;
@@ -328,9 +347,7 @@ static std::vector<std::vector<ExPolygons>> slices_to_regions(
                 std::vector<RegionSlice> temp_slices;
                 for (size_t zs_complex_idx = range.begin(); zs_complex_idx < range.end(); ++ zs_complex_idx) {
                     auto [z_idx, z] = zs_complex[zs_complex_idx];
-                    for (; it_layer_range->layer_height_range.second <= z; ++ it_layer_range)
-                        assert(it_layer_range != print_object_regions.layer_ranges.end());
-                    assert(it_layer_range != print_object_regions.layer_ranges.end() && it_layer_range->layer_height_range.first <= z && z < it_layer_range->layer_height_range.second);
+                    it_layer_range = layer_range_next(print_object_regions.layer_ranges, it_layer_range, z);
                     const PrintObjectRegions::LayerRangeRegions &layer_range = *it_layer_range;
                     {
                         std::vector<VolumeSlices*> &layer_range_regions_to_slices = layer_ranges_regions_to_slices[it_layer_range - print_object_regions.layer_ranges.begin()];
@@ -575,57 +592,6 @@ void PrintObject::slice_volumes()
     }
     region_slices.clear();
     
-#if 0
-        // Second clip the volumes in the order they are presented at the user interface.
-        BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - parallel clipping - start";
-        tbb::parallel_for(
-            tbb::blocked_range<size_t>(0, slice_zs.size()),
-            [this, &sliced_volumes, num_modifiers](const tbb::blocked_range<size_t>& range) {
-                float delta   = float(scale_(m_config.xy_size_compensation.value));
-                // Only upscale together with clipping if there are no modifiers, as the modifiers shall be applied before upscaling
-                // (upscaling may grow the object outside of the modifier mesh).
-                bool  upscale = delta > 0 && num_modifiers == 0;
-                for (size_t layer_id = range.begin(); layer_id < range.end(); ++ layer_id) {
-                    m_print->throw_if_canceled();
-                    // Trim volumes in a single layer, one by the other, possibly apply upscaling.
-                    {
-                        Polygons processed;
-                        for (SlicedVolume &sliced_volume : sliced_volumes) 
-                        	if (! sliced_volume.expolygons_by_layer.empty()) {
-	                            ExPolygons slices = std::move(sliced_volume.expolygons_by_layer[layer_id]);
-	                            if (upscale)
-	                                slices = offset_ex(std::move(slices), delta);
-	                            if (! processed.empty())
-	                                // Trim by the slices of already processed regions.
-	                                slices = diff_ex(slices, processed);
-	                            if (size_t(&sliced_volume - &sliced_volumes.front()) + 1 < sliced_volumes.size())
-	                                // Collect the already processed regions to trim the to be processed regions.
-	                                polygons_append(processed, slices);
-	                            sliced_volume.expolygons_by_layer[layer_id] = std::move(slices);
-	                        }
-                    }
-                    // Collect and union volumes of a single region.
-                    for (int region_id = 0; region_id < int(m_region_volumes.size()); ++ region_id) {
-                        ExPolygons expolygons;
-                        size_t     num_volumes = 0;
-                        for (SlicedVolume &sliced_volume : sliced_volumes)
-                            if (sliced_volume.region_id == region_id && ! sliced_volume.expolygons_by_layer.empty() && ! sliced_volume.expolygons_by_layer[layer_id].empty()) {
-                                ++ num_volumes;
-                                append(expolygons, std::move(sliced_volume.expolygons_by_layer[layer_id]));
-                            }
-                        if (num_volumes > 1)
-                            // Merge the islands using a positive / negative offset.
-                            expolygons = offset_ex(offset_ex(expolygons, float(scale_(EPSILON))), -float(scale_(EPSILON)));
-                        m_layers[layer_id]->regions()[region_id]->slices.append(std::move(expolygons), stInternal);
-                    }
-                }
-            });
-        BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - parallel clipping - end";
-        clipped  = true;
-        upscaled = m_config.xy_size_compensation.value > 0 && num_modifiers == 0;
-    }
-#endif
-
     BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - removing top empty layers";
     while (! m_layers.empty()) {
         const Layer *layer = m_layers.back();
@@ -638,6 +604,124 @@ void PrintObject::slice_volumes()
         m_layers.back()->upper_layer = nullptr;
     m_print->throw_if_canceled();
 
+    // Is any ModelVolume MMU painted?
+    if (const auto &volumes = this->model_object()->volumes;
+        std::find_if(volumes.begin(), volumes.end(), [](const ModelVolume *v) { return ! v->mmu_segmentation_facets.empty(); }) != volumes.end()) {
+        BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - MMU segmentation";
+        // Returns MMU segmentation based on painting in MMU segmentation gizmo
+        std::vector<std::vector<std::pair<ExPolygon, size_t>>> segmentation = multi_material_segmentation_by_painting(*this);
+        assert(segmentation.size() == m_layers.size());
+        tbb::parallel_for(
+            tbb::blocked_range<size_t>(0, segmentation.size(), std::max(segmentation.size() / 128, size_t(1))),
+            [this, &segmentation](const tbb::blocked_range<size_t> &range) {
+                const auto  &layer_ranges   = this->m_shared_regions->layer_ranges;
+                double       z              = m_layers[range.begin()]->slice_z;
+                auto         it_layer_range = layer_range_first(layer_ranges, z);
+                const size_t num_extruders = this->print()->config().nozzle_diameter.size();
+                struct ByExtruder {
+                    ExPolygons  expolygons;
+                    BoundingBox bbox;
+                };
+                std::vector<ByExtruder> by_extruder;
+                struct ByRegion {
+                    ExPolygons  expolygons;
+                    bool        needs_merge { false };
+                };
+                std::vector<ByRegion> by_region;
+                for (size_t layer_id = range.begin(); layer_id < range.end(); ++ layer_id) {
+                    m_print->throw_if_canceled();
+                    Layer *layer = m_layers[layer_id];
+                    it_layer_range = layer_range_next(layer_ranges, it_layer_range, layer->slice_z);
+                    const PrintObjectRegions::LayerRangeRegions &layer_range = *it_layer_range;
+                    // Gather per extruder expolygons.
+                    by_extruder.assign(num_extruders, ByExtruder());
+                    by_region.assign(layer->m_regions.size(), ByRegion());
+                    bool layer_split = false;
+                    for (size_t extruder_id = 0; extruder_id < num_extruders; ++ extruder_id) {
+                        ByExtruder &region = by_extruder[extruder_id];
+                        for (const std::pair<ExPolygon, size_t> &colored_polygon : segmentation[layer_id])
+                            if (colored_polygon.second == extruder_id)
+                                region.expolygons.emplace_back(std::move(colored_polygon.first));
+                        if (! region.expolygons.empty()) {
+                            region.bbox = get_extents(region.expolygons);
+                            layer_split = true;
+                        }
+                    }
+                    if (! layer_split)
+                        continue;
+                    // Split LayerRegions by by_extruder regions.
+                    auto it_painted_region = layer_range.painted_regions.begin();
+                    for (size_t region_id = 0; region_id < layer->m_regions.size(); ++ region_id)
+                        if (LayerRegion &layerm = *layer->m_regions[region_id]; ! layerm.slices.surfaces.empty()) {
+                            const BoundingBox bbox = get_extents(layerm.slices.surfaces);
+                            assert(it_painted_region < layer_range.painted_regions.end());
+                            for (; layer_range.volume_regions[it_painted_region->parent].region->print_object_region_id() < region_id; ++ it_painted_region)
+                                assert(it_painted_region < layer_range.painted_regions.end());
+                            assert(&layerm.region() == it_painted_region->region && layerm.region().print_object_region_id() == region_id);
+                            // 1-based extruder ID
+                            bool   self_trimmed = false;
+                            size_t self_extruder_id;
+                            for (size_t extruder_id = 1; extruder_id <= by_extruder.size(); ++ extruder_id)
+                                if (ByExtruder &segmented = by_extruder[extruder_id - 1]; segmented.bbox.defined && bbox.overlap(segmented.bbox)) {
+                                    // Find the target region.
+                                    for (; it_painted_region->extruder_id < extruder_id; ++ it_painted_region)
+                                        assert(it_painted_region < layer_range.painted_regions.end());
+                                    assert(layer_range.volume_regions[it_painted_region->parent].region == &layerm.region() && it_painted_region->extruder_id == extruder_id);
+                                    //FIXME Don't trim by self, it is not reliable.
+                                    if (&layerm.region() == it_painted_region->region) {
+                                        self_extruder_id = extruder_id;
+                                        continue;
+                                    }
+                                    // Steal from this region.
+                                    int         target_region_id = it_painted_region->region->print_object_region_id();
+                                    ExPolygons  stolen           = intersection_ex(layerm.slices.surfaces, segmented.expolygons);
+                                    if (! stolen.empty()) {
+                                        ByRegion &dst = by_region[target_region_id];
+                                        if (dst.expolygons.empty()) {
+                                            dst.expolygons = std::move(stolen);
+                                        } else {
+                                            append(dst.expolygons, std::move(stolen));
+                                            dst.needs_merge = true;
+                                        }
+                                    }
+#if 0
+                                    if (&layerm.region() == it_painted_region->region)
+                                        // Slices of this LayerRegion were trimmed by a MMU region of the same PrintRegion.
+                                        self_trimmed = true;
+#endif
+                                }
+                            if (! self_trimmed) {
+                                // Trim slices of this LayerRegion with all the MMU regions.
+                                Polygons mine = to_polygons(std::move(layerm.slices.surfaces));
+                                for (auto &segmented : by_extruder)
+                                    if (&segmented - by_extruder.data() + 1 != self_extruder_id && segmented.bbox.defined && bbox.overlap(segmented.bbox)) {
+                                        mine = diff(mine, segmented.expolygons);
+                                        if (mine.empty())
+                                            break;
+                                    }
+                                if (! mine.empty()) {
+                                    ByRegion &dst = by_region[layerm.region().print_object_region_id()];
+                                    if (dst.expolygons.empty()) {
+                                        dst.expolygons = union_ex(mine);
+                                    } else {
+                                        append(dst.expolygons, union_ex(mine));
+                                        dst.needs_merge = true;
+                                    }
+                                }
+                            }
+                        }
+                    // Re-create Surfaces of LayerRegions.
+                    for (size_t region_id = 0; region_id < layer->m_regions.size(); ++ region_id) {
+                        ByRegion &src = by_region[region_id];
+                        if (src.needs_merge)
+                            // Multiple regions were merged into one.
+                            src.expolygons = offset2_ex(src.expolygons, float(scale_(EPSILON)), - float(scale_(EPSILON)));
+                        layer->m_regions[region_id]->slices.set(std::move(src.expolygons), stInternal);
+                    }
+                }
+            });
+    }
+
     BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - make_slices in parallel - begin";
     {
         // Compensation value, scaled. Only applying the negative scaling here, as the positive scaling has already been applied during slicing.
@@ -650,8 +734,7 @@ void PrintObject::slice_volumes()
 	    ExPolygons  lslices_1st_layer;
 	    tbb::parallel_for(
 	        tbb::blocked_range<size_t>(0, m_layers.size()),
-			[this, xy_compensation_scaled, elephant_foot_compensation_scaled, &lslices_1st_layer]
-				(const tbb::blocked_range<size_t>& range) {
+			[this, xy_compensation_scaled, elephant_foot_compensation_scaled, &lslices_1st_layer](const tbb::blocked_range<size_t>& range) {
 	            for (size_t layer_id = range.begin(); layer_id < range.end(); ++ layer_id) {
 	                m_print->throw_if_canceled();
 	                Layer *layer = m_layers[layer_id];