ENH: model with a volume but multi-mesh should can be mesh union

As title

Signed-off-by: salt.wei <salt.wei@bambulab.com>
Change-Id: I4cf12198980a9a5a7d8dbbfc49fd5d807ca97902

src/slic3r/GUI/GUI_Factories.cpp

@@ -927,7 +927,7 @@ void MenuFactory::append_menu_item_merge_parts_to_single_part(wxMenu* menu)
     menu->AppendSeparator();
     append_menu_item(menu, wxID_ANY, _L("Mesh boolean"), _L("Mesh boolean operations including union and subtraction"),
         [](wxCommandEvent&) { obj_list()->boolean/*merge_volumes*/(); }, "", menu,
-        []() { return obj_list()->can_merge_to_single_object(); }, m_parent);
+        []() { return obj_list()->can_mesh_boolean(); }, m_parent);
 }
 
 void MenuFactory::append_menu_items_mirror(wxMenu* menu)

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -3076,6 +3076,16 @@ bool ObjectList::can_merge_to_single_object() const
     return (*m_objects)[obj_idx]->volumes.size() > 1;
 }
 
+bool ObjectList::can_mesh_boolean() const
+{
+    int obj_idx = get_selected_obj_idx();
+    if (obj_idx < 0)
+        return false;
+
+    // selected object should be multi mesh
+    return (*m_objects)[obj_idx]->volumes.size() > 1 || ((*m_objects)[obj_idx]->volumes.size() == 1 && (*m_objects)[obj_idx]->volumes[0]->is_splittable());
+}
+
 bool ObjectList::has_selected_cut_object() const
 {
     wxDataViewItemArray sels;

src/slic3r/GUI/GUI_ObjectList.hpp

@@ -311,6 +311,7 @@ public:
     bool                can_split_instances();
     bool                can_merge_to_multipart_object() const;
     bool                can_merge_to_single_object() const;
+    bool                can_mesh_boolean() const;
 
     bool                has_selected_cut_object() const;
     void                invalidate_cut_info_for_selection();