Fixed undo/redo issue when clear method of FacetsAnnotation and ModelConfig

reset timestamp to 1. This led to a bug where e.g. deleting painted facets
through the respective item in object list followed by  possible other actions
and undo restored the painted facets from the time when the project was loaded.
I'm not sure if there was any other situation where this problem manifested.

src/libslic3r/Model.cpp

@@ -1198,9 +1198,9 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, ModelObjectCutAttr
     for (ModelVolume *volume : volumes) {
         const auto volume_matrix = volume->get_matrix();
 
-        volume->supported_facets.clear();
-        volume->seam_facets.clear();
-        volume->mmu_segmentation_facets.clear();
+        volume->supported_facets.reset();
+        volume->seam_facets.reset();
+        volume->mmu_segmentation_facets.reset();
 
         if (! volume->is_model_part()) {
             // Modifiers are not cut, but we still need to add the instance transformation
@@ -2019,11 +2019,11 @@ bool FacetsAnnotation::set(const TriangleSelector& selector)
     return false;
 }
 
-void FacetsAnnotation::clear()
+void FacetsAnnotation::reset()
 {
     m_data.first.clear();
     m_data.second.clear();
-    this->reset_timestamp();
+    this->touch();
 }
 
 // Following function takes data from a triangle and encodes it as string

src/libslic3r/Model.hpp

@@ -541,7 +541,10 @@ public:
     indexed_triangle_set get_facets_strict(const ModelVolume& mv, EnforcerBlockerType type) const;
     bool has_facets(const ModelVolume& mv, EnforcerBlockerType type) const;
     bool empty() const { return m_data.first.empty(); }
-    void clear();
+
+    // Following method clears the config and increases its timestamp, so the deleted
+    // state is considered changed from perspective of the undo/redo stack.
+    void reset();
 
     // Serialize triangle into string, for serialization into 3MF/AMF.
     std::string get_triangle_as_string(int i) const;

src/libslic3r/ObjectID.hpp

@@ -105,9 +105,6 @@ protected:
 	// The class tree will have virtual tables and type information.
 	virtual ~ObjectWithTimestamp() = default;
 
-    // Resetting timestamp to 1 indicates the object is in its initial (cleared) state.
-    // To be called by the derived class's clear() method.
-    void                reset_timestamp() { m_timestamp = 1; }
     // The timestamp uniquely identifies content of the derived class' data, therefore it makes sense to copy the timestamp if the content data was copied.
     void                copy_timestamp(const ObjectWithTimestamp& rhs) { m_timestamp = rhs.m_timestamp; }
 

src/libslic3r/PrintConfig.hpp

@@ -1064,7 +1064,9 @@ Points get_bed_shape(const SLAPrinterConfig &cfg);
 class ModelConfig
 {
 public:
-    void         clear() { m_data.clear(); m_timestamp = 1; }
+    // Following method clears the config and increases its timestamp, so the deleted
+    // state is considered changed from perspective of the undo/redo stack.
+    void         reset() { m_data.clear(); touch(); }
 
     void         assign_config(const ModelConfig &rhs) {
         if (m_timestamp != rhs.m_timestamp) {
@@ -1076,7 +1078,7 @@ public:
         if (m_timestamp != rhs.m_timestamp) {
             m_data      = std::move(rhs.m_data);
             m_timestamp = rhs.m_timestamp;
-            rhs.clear();
+            rhs.reset();
         }
     }
 

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -1803,21 +1803,21 @@ void ObjectList::del_info_item(const int obj_idx, InfoItemType type)
         cnv->get_gizmos_manager().reset_all_states();
         Plater::TakeSnapshot(plater, _L("Remove paint-on supports"));
         for (ModelVolume* mv : (*m_objects)[obj_idx]->volumes)
-            mv->supported_facets.clear();
+            mv->supported_facets.reset();
         break;
 
     case InfoItemType::CustomSeam:
         cnv->get_gizmos_manager().reset_all_states();
         Plater::TakeSnapshot(plater, _L("Remove paint-on seam"));
         for (ModelVolume* mv : (*m_objects)[obj_idx]->volumes)
-            mv->seam_facets.clear();
+            mv->seam_facets.reset();
         break;
 
     case InfoItemType::MmuSegmentation:
         cnv->get_gizmos_manager().reset_all_states();
         Plater::TakeSnapshot(plater, _L("Remove Multi Material painting"));
         for (ModelVolume* mv : (*m_objects)[obj_idx]->volumes)
-            mv->mmu_segmentation_facets.clear();
+            mv->mmu_segmentation_facets.reset();
         break;
 
     case InfoItemType::Sinking:
@@ -1856,7 +1856,7 @@ void ObjectList::del_settings_from_config(const wxDataViewItem& parent_item)
     if (is_layer_settings)
         layer_height = m_config->opt_float("layer_height");
 
-    m_config->clear();
+    m_config->reset();
 
     if (extruder >= 0)
         m_config->set_key_value("extruder", new ConfigOptionInt(extruder));
@@ -1932,7 +1932,7 @@ bool ObjectList::del_subobject_from_object(const int obj_idx, const int idx, con
             const auto last_volume = object->volumes[0];
             if (!last_volume->config.empty()) {
                 object->config.apply(last_volume->config);
-                last_volume->config.clear();
+                last_volume->config.reset();
 
                 // update extruder color in ObjectList
                 wxDataViewItem obj_item = m_objects_model->GetItemById(obj_idx);
@@ -3769,7 +3769,7 @@ void ObjectList::last_volume_is_deleted(const int obj_idx)
     auto volume = (*m_objects)[obj_idx]->volumes.front();
 
     // clear volume's config values
-    volume->config.clear();
+    volume->config.reset();
 
     // set a default extruder value, since user can't add it manually
     volume->config.set_key_value("extruder", new ConfigOptionInt(0));

src/slic3r/GUI/Plater.cpp

@@ -6217,9 +6217,9 @@ void Plater::clear_before_change_mesh(int obj_idx)
     bool paint_removed = false;
     for (ModelVolume* mv : mo->volumes) {
         paint_removed |= ! mv->supported_facets.empty() || ! mv->seam_facets.empty() || ! mv->mmu_segmentation_facets.empty();
-        mv->supported_facets.clear();
-        mv->seam_facets.clear();
-        mv->mmu_segmentation_facets.clear();
+        mv->supported_facets.reset();
+        mv->seam_facets.reset();
+        mv->mmu_segmentation_facets.reset();
     }
     if (paint_removed) {
         // snapshot_time is captured by copy so the lambda knows where to undo/redo to.