Fixed regression of 71fa411100

where the PrintObject bounding box was not invalidated correctly
when the transformation matrices of instances changed.

Also refactored PrintObject::size() for const correctness.

src/libslic3r/GCode.cpp

@@ -1091,7 +1091,7 @@ namespace DoExport {
 static inline std::vector<const PrintInstance*> sort_object_instances_by_max_z(const Print &print)
 {
     std::vector<const PrintObject*> objects(print.objects().begin(), print.objects().end());
-	std::sort(objects.begin(), objects.end(), [](const PrintObject *po1, const PrintObject *po2) { return po1->size(2) < po2->size(2); });
+	std::sort(objects.begin(), objects.end(), [](const PrintObject *po1, const PrintObject *po2) { return po1->size()(2) < po2->size()(2); });
 	std::vector<const PrintInstance*> instances;
 	instances.reserve(objects.size());
 	for (const PrintObject *object : objects)

src/libslic3r/Model.cpp

@@ -907,10 +907,8 @@ const BoundingBoxf3& ModelObject::raw_bounding_box() const
 
         const Transform3d& inst_matrix = this->instances.front()->get_transformation().get_matrix(true);
         for (const ModelVolume *v : this->volumes)
-        {
             if (v->is_model_part())
                 m_raw_bounding_box.merge(v->mesh().transformed_bounding_box(inst_matrix * v->get_matrix()));
-        }
     }
 	return m_raw_bounding_box;
 }

src/libslic3r/Print.cpp

@@ -836,7 +836,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
         // Update the ModelObject instance, possibly invalidate the linked PrintObjects.
         assert(it_status->status == ModelObjectStatus::Old || it_status->status == ModelObjectStatus::Moved);
         // Check whether a model part volume was added or removed, their transformations or order changed.
-        // Only volume IDs, volume types and their order are checked, configuration and other parameters are NOT checked.
+        // Only volume IDs, volume types, transformation matrices and their order are checked, configuration and other parameters are NOT checked.
         bool model_parts_differ         = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::MODEL_PART);
         bool modifiers_differ           = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::PARAMETER_MODIFIER);
         bool support_blockers_differ    = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::SUPPORT_BLOCKER);
@@ -899,10 +899,14 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
 	                model_object.instances.emplace_back(new ModelInstance(*model_instance));
 	                model_object.instances.back()->set_model_object(&model_object);
 	            }
-	        } else {
+	        } else if (! std::equal(model_object.instances.begin(), model_object.instances.end(), model_object_new.instances.begin(), 
-	        	// Just synchronize the content of the instances. This avoids memory allocation and it does not invalidate ModelInstance pointers,
+	        		[](auto l, auto r){ return l->print_volume_state == r->print_volume_state && l->printable == r->printable && 
-	        	// which may be accessed by G-code export in the meanwhile to deduce sequential print order.
+	        						           l->get_transformation().get_matrix().isApprox(r->get_transformation().get_matrix()); })) {
-                auto new_instance = model_object_new.instances.begin();
+	        	// If some of the instances changed, the bounding box of the updated ModelObject is likely no more valid.
+	        	// This is safe as the ModelObject's bounding box is only accessed from this function, which is called from the main thread only.
+	 			model_object.invalidate_bounding_box();
+	        	// Synchronize the content of instances.
+	        	auto new_instance = model_object_new.instances.begin();
 				for (auto old_instance = model_object.instances.begin(); old_instance != model_object.instances.end(); ++ old_instance, ++ new_instance) {
 					(*old_instance)->set_transformation((*new_instance)->get_transformation());
                     (*old_instance)->print_volume_state = (*new_instance)->print_volume_state;
@@ -1197,7 +1201,7 @@ std::string Print::validate() const
         {
             std::vector<coord_t> object_height;
             for (const PrintObject *object : m_objects)
-                object_height.insert(object_height.end(), object->instances().size(), object->size(2));
+                object_height.insert(object_height.end(), object->instances().size(), object->size()(2));
             std::sort(object_height.begin(), object_height.end());
             // Ignore the tallest *copy* (this is why we repeat height for all of them):
             // it will be printed as last one so its height doesn't matter.
@@ -1429,7 +1433,7 @@ BoundingBox Print::bounding_box() const
     for (const PrintObject *object : m_objects)
         for (const PrintInstance &instance : object->instances()) {
             bb.merge(instance.shift);
-            bb.merge(instance.shift + to_2d(object->size));
+            bb.merge(instance.shift + to_2d(object->size()));
         }
     return bb;
 }

src/libslic3r/Print.hpp

@@ -120,17 +120,17 @@ public:
     // so that next call to make_perimeters() performs a union() before computing loops
     bool                    typed_slices;
 
-    Vec3crd                 size;           // XYZ in scaled coordinates
+    // XYZ in scaled coordinates
-
+    const Vec3crd&           size() const			{ return m_size; }
     const PrintObjectConfig& config() const         { return m_config; }    
     const LayerPtrs&        layers() const          { return m_layers; }
     const SupportLayerPtrs& support_layers() const  { return m_support_layers; }
     const Transform3d&      trafo() const           { return m_trafo; }
     const PrintInstances&   instances() const       { return m_instances; }
-    const Point 			instance_center(size_t idx) const { return m_instances[idx].shift + m_copies_shift + Point(this->size.x() / 2, this->size.y() / 2); }
+    const Point 			instance_center(size_t idx) const { return m_instances[idx].shift + m_copies_shift + Point(this->size().x() / 2, this->size().y() / 2); }
 
     // since the object is aligned to origin, bounding box coincides with size
-    BoundingBox bounding_box() const { return BoundingBox(Point(0,0), to_2d(this->size)); }
+    BoundingBox bounding_box() const { return BoundingBox(Point(0,0), to_2d(this->size())); }
 
     // adds region_id, too, if necessary
     void add_region_volume(unsigned int region_id, int volume_id, const t_layer_height_range &layer_range) {
@@ -235,6 +235,8 @@ private:
     void combine_infill();
     void _generate_support_material();
 
+    // XYZ in scaled coordinates
+    Vec3crd									m_size;
     PrintObjectConfig                       m_config;
     // Translation in Z + Rotation + Scaling / Mirroring.
     Transform3d                             m_trafo = Transform3d::Identity();

src/libslic3r/PrintObject.cpp

@@ -43,7 +43,7 @@ namespace Slic3r {
 PrintObject::PrintObject(Print* print, ModelObject* model_object, bool add_instances) :
     PrintObjectBaseWithState(print, model_object),
     typed_slices(false),
-    size(Vec3crd::Zero())
+    m_size(Vec3crd::Zero())
 {
     // Compute the translation to be applied to our meshes so that we work with smaller coordinates
     {
@@ -56,7 +56,7 @@ PrintObject::PrintObject(Print* print, ModelObject* model_object, bool add_insta
         const BoundingBoxf3 modobj_bbox = model_object->raw_bounding_box();
         m_copies_shift = Point::new_scale(modobj_bbox.min(0), modobj_bbox.min(1));
         // Scale the object size and store it
-        this->size = (modobj_bbox.size() * (1. / SCALING_FACTOR)).cast<coord_t>();
+        this->m_size = (modobj_bbox.size() * (1. / SCALING_FACTOR)).cast<coord_t>();
     }
     
     if (add_instances) {
@@ -1450,7 +1450,7 @@ void PrintObject::update_slicing_parameters()
 {
     if (! m_slicing_params.valid)
         m_slicing_params = SlicingParameters::create_from_config(
-            this->print()->config(), m_config, unscale<double>(this->size(2)), this->object_extruders());
+            this->print()->config(), m_config, unscale<double>(this->size()(2)), this->object_extruders());
 }
 
 SlicingParameters PrintObject::slicing_parameters(const DynamicPrintConfig& full_config, const ModelObject& model_object, float object_max_z)