Avoid unnecessary mesh duplication for the objects with modifiers

addons/io_scene_gltf2/__init__.py

@@ -659,6 +659,13 @@ class ExportGLTF2_Base(ConvertGLTF2_Base):
         default=False
     )
 
+    export_compare_meshes: BoolProperty(
+        name='Compare meshes',
+        description='Compare mesh objects after applying modifiers '
+                    '(to avoid duplication of identical meshes in the exported file)',
+        default=False
+    )
+
     export_shared_accessors: BoolProperty(
         name='Shared Accessors',
         description='Export Primitives using shared accessors for attributes',
@@ -1200,6 +1207,7 @@ def execute(self, context):
         export_settings['gltf_extras'] = self.export_extras
         export_settings['gltf_yup'] = self.export_yup
         export_settings['gltf_apply'] = self.export_apply
+        export_settings['gltf_compare_meshes'] = self.export_compare_meshes
         export_settings['gltf_shared_accessors'] = self.export_shared_accessors
         export_settings['gltf_current_frame'] = self.export_current_frame
         export_settings['gltf_animations'] = self.export_animations
@@ -1497,6 +1505,7 @@ def export_panel_data_mesh(layout, operator):
     header.label(text="Mesh")
     if body:
         body.prop(operator, 'export_apply')
+        body.prop(operator, 'export_compare_meshes')
         body.prop(operator, 'export_texcoords')
         body.prop(operator, 'export_normals')
         col = body.column()

addons/io_scene_gltf2/blender/exp/gather.py

@@ -111,6 +111,7 @@ def __gather_scene(blender_scene, export_settings):
     export_user_extensions('vtree_after_filter_hook', export_settings, vtree)
 
     export_settings['vtree'] = vtree
+    export_settings['mesh_instances'] = {}
 
     # If we don't remove armature object, we can't have bones directly at root of scene
     # So looping only on root nodes, as they are all nodes, not bones
@@ -149,6 +150,8 @@ def __gather_scene(blender_scene, export_settings):
 
     export_user_extensions('gather_scene_hook', export_settings, scene, blender_scene)
 
+    export_settings['mesh_instances'].clear()
+
     return scene
 
 

addons/io_scene_gltf2/blender/exp/nodes.py

@@ -262,6 +262,8 @@ def __gather_matrix(blender_object, export_settings):
 
 
 def __gather_mesh(vnode, blender_object, export_settings):
+    need_to_mesh_clear = False
+
     if vnode.blender_type == VExportNode.COLLECTION:
         return None
     if blender_object and blender_object.type in ['CURVE', 'SURFACE', 'FONT']:
@@ -319,6 +321,8 @@ def __gather_mesh(vnode, blender_object, export_settings):
                 depsgraph = bpy.context.evaluated_depsgraph_get()
                 blender_mesh_owner = blender_object.evaluated_get(depsgraph)
                 blender_mesh = blender_mesh_owner.to_mesh(preserve_all_data_layers=True, depsgraph=depsgraph)
+                need_to_mesh_clear = True
+
                 # Seems now (from 4.2) the custom properties are Statically Typed
                 # so no need to copy them in that case, because overwriting them will crash
                 if len(blender_mesh.keys()) == 0:
@@ -332,6 +336,23 @@ def __gather_mesh(vnode, blender_object, export_settings):
                 # Store that this evaluated mesh has been created by the exporter, and is not a GN instance mesh
                 blender_mesh['gltf2_mesh_applied'] = True
 
+                # check if other object used the same origin mesh produced the same mesh after modifier applies, if yes use this mesh
+                if export_settings["gltf_compare_meshes"]:
+                    if not blender_object.data in export_settings["mesh_instances"]:
+                        # make own copy of mesh because result of `to_mesh` is temporary
+                        # (and can be overwrite for example by call `to_mesh` on same object in other instance of collection)
+                        blender_mesh = blender_mesh.copy()
+                        export_settings["mesh_instances"][blender_object.data] = [blender_mesh]
+                    else:
+                        for other_mesh in export_settings["mesh_instances"][blender_object.data]:
+                            compare = blender_mesh.unit_test_compare(mesh=other_mesh)
+                            if compare == "Same":
+                                blender_mesh = other_mesh
+                                break
+                        else:
+                            blender_mesh = blender_mesh.copy()
+                            export_settings["mesh_instances"][blender_object.data].append(blender_mesh)
+
                 if export_settings['gltf_skins']:
                     # restore Armature modifiers
                     for idx, show_viewport in armature_modifiers.items():
@@ -348,12 +369,6 @@ def __gather_mesh(vnode, blender_object, export_settings):
 
         else:
             blender_mesh = blender_object.data
-            if not export_settings['gltf_skins']:
-                modifiers = None
-            else:
-                # Check if there is an armature modidier
-                if len([mod for mod in blender_object.modifiers if mod.type == "ARMATURE"]) == 0:
-                    modifiers = None
 
             # Keep materials from object, as no modifiers are applied, so no risk that
             # modifiers changed them
@@ -369,6 +384,12 @@ def __gather_mesh(vnode, blender_object, export_settings):
                 if modifier.type == 'ARMATURE':
                     uuid_for_skined_data = vnode.uuid
 
+        # no need keep modifiers if skins are not exported or object don't have an armature modifier
+        # (applying different set of modifiers results in different blender_mesh object)
+        # so set it to None to avoid unnecessary mesh duplication
+        if uuid_for_skined_data is None:
+            modifiers = None
+
     result = gltf2_blender_gather_mesh.gather_mesh(blender_mesh,
                                                    uuid_for_skined_data,
                                                    blender_object.vertex_groups if blender_object else None,
@@ -377,7 +398,7 @@ def __gather_mesh(vnode, blender_object, export_settings):
                                                    None,
                                                    export_settings)
 
-    if export_settings['gltf_apply'] and modifiers is not None:
+    if need_to_mesh_clear:
         blender_mesh_owner.to_mesh_clear()
 
     return result