fix(merge groups): fix buggy merge groups when objects were duplicated

Change how the merge group system works under the hood to take into account when objects are
duplicated, which in Blender is just a straight duplication of the data block with no events to
trigger a merge group update on. This new solution uses a bunch of lookups instead, but in the most
optimised way possible

Fix #187

addon/i3dio/ui/object.py

@@ -559,34 +559,14 @@ def draw(self, context):
             obj.i3d_attributes.property_unset('weather_required_mask')
             obj.i3d_attributes.property_unset('weather_prevent_mask')
 
-@register
-class I3DMergeGroupMemberObject(bpy.types.PropertyGroup):
-    object: PointerProperty(
-        name="Merge Group Member",
-        type=bpy.types.Object,
-		)
-
 @register
 class I3DMergeGroup(bpy.types.PropertyGroup):
-    def add_member(self, member_object):
-        self.members.add().object = member_object
-
-    def remove_member(self, member_object):
-        for idx,member in enumerate(self.members):
-            if member.object is member_object:
-                self.members.remove(idx)
-
     name: StringProperty(
         name='Merge Group Name',
         description='The name of the merge group',
         default='MergeGroup'
     )
 
-    members: CollectionProperty(
-        name="Members",
-        description="Members of the merge group",
-        type=I3DMergeGroupMemberObject)
-
     root: PointerProperty(
         name="Merge Group Root Object",
         description="The object acting as the root for the merge group",
@@ -630,7 +610,7 @@ def draw(self, context):
             col = row.column(align=True)
             col.operator('i3dio.new_merge_group', text="", icon='DUPLICATE')
             col = row.column(align=True)
-            col.operator('i3dio.remove_merge_group', text="", icon='PANEL_CLOSE')
+            col.operator('i3dio.remove_from_merge_group', text="", icon='PANEL_CLOSE')
 
 
 @register
@@ -651,10 +631,13 @@ def execute(self, context):
         obj = context.object
         selected_mg_index = int(self.enum)
         if obj.i3d_merge_group_index != selected_mg_index:
-            context.scene.i3dio_merge_groups[obj.i3d_merge_group_index].remove_member(obj)
-            context.scene.i3dio_merge_groups[selected_mg_index].add_member(obj)
+            old_mg_index = obj.i3d_merge_group_index
             obj.i3d_merge_group_index = selected_mg_index
+            if old_mg_index != -1:
+                remove_merge_group_if_empty(context, old_mg_index)
             context.area.tag_redraw()
+        else:
+            print("same mg")
         return {"FINISHED"}
 
     def invoke(self, context, event):
@@ -678,30 +661,42 @@ def execute(self, context):
             name = f"{MERGE_GROUP_DEFAULT_NAME}.{count:03d}"
             count += 1
         mg = context.scene.i3dio_merge_groups.add()
-        if obj.i3d_merge_group_index != -1:
-            context.scene.i3dio_merge_groups[obj.i3d_merge_group_index].remove_member(obj)
+
         mg.name = name
         mg.root = obj
-        mg.add_member(obj)
+        old_mg_index = obj.i3d_merge_group_index
         obj.i3d_merge_group_index = len(context.scene.i3dio_merge_groups) - 1
+        if old_mg_index != -1:
+            remove_merge_group_if_empty(context, old_mg_index)
         return {'FINISHED'}
 
-
+def remove_merge_group_if_empty(context, mg_index):
+    mg_member_count = 0
+    objects_in_higher_indexed_merge_groups = []
+    for obj in context.scene.objects:
+        if obj.type == 'MESH' and obj.i3d_merge_group_index != -1:
+            if obj.i3d_merge_group_index == mg_index:
+                mg_member_count += 1
+            else:
+                objects_in_higher_indexed_merge_groups.append(obj)
+    if mg_member_count == 0:
+        context.scene.i3dio_merge_groups.remove(mg_index)
+        for obj in objects_in_higher_indexed_merge_groups[mg_index::]:
+            obj.i3d_merge_group_index -= 1
+    else:
+        print(f"{mg_member_count} members left in '{context.scene.i3dio_merge_groups[mg_index]}'")
+
 @register
-class I3D_IO_OT_remove_merge_group(bpy.types.Operator):
-    bl_idname = "i3dio.remove_merge_group"
+class I3D_IO_OT_remove_from_merge_group(bpy.types.Operator):
+    bl_idname = "i3dio.remove_from_merge_group"
     bl_label = "Remove From Merge Group"
     bl_description = "Remove this object from it's current merge group"
     bl_options = {'INTERNAL', 'UNDO'}
 
     def execute(self, context):
-        mg_index = context.object.i3d_merge_group_index
-        for member in context.scene.i3dio_merge_groups[mg_index].members:
-            member.object.i3d_merge_group_index = -1
-        context.scene.i3dio_merge_groups.remove(mg_index)
-        for mg in context.scene.i3dio_merge_groups[mg_index::]:
-            for member in mg.members:
-                member.object.i3d_merge_group_index -= 1
+        old_mg_index = context.object.i3d_merge_group_index
+        context.object.i3d_merge_group_index = -1
+        remove_merge_group_if_empty(context, old_mg_index)
         return {'FINISHED'}
 
 @register
@@ -731,21 +726,12 @@ def poll(cls, context):
         return context.object.i3d_merge_group_index != -1
 
     def execute(self, context):
-        for member in context.scene.i3dio_merge_groups[context.object.i3d_merge_group_index].members:
-            if member.object is not None:
-                member.object.select_set(True)
-            else:
-                print("Deleted Member Object")
+        for obj in context.scene.objects:
+            mg_index = context.object.i3d_merge_group_index
+            if obj.i3d_merge_group_index == mg_index:
+                obj.select_set(True)
         return {'FINISHED'}
 
-@persistent
-def prune_merge_groups(dummy):
-    for scene in bpy.data.scenes:
-        for mg in scene.i3dio_merge_groups:
-            for idx, member in reversed(list(enumerate(mg.members))):
-                if member.object is None:
-                    mg.members.remove(idx)
-
 @persistent
 def handle_old_merge_groups(dummy):
     for scene in bpy.data.scenes:
@@ -761,7 +747,6 @@ def handle_old_merge_groups(dummy):
                         mg = scene.i3dio_merge_groups.add()
                         mg.name = group_id
                         obj.i3d_merge_group_index = len(scene.i3dio_merge_groups) - 1
-                    mg.add_member(obj)
                     if is_root != None and is_root == 1:
                         mg.root = obj
                 del obj['i3d_merge_group']
@@ -854,12 +839,10 @@ def register():
     bpy.types.Object.i3d_merge_group_index = IntProperty(default = -1)
     bpy.types.Object.i3d_mapping = PointerProperty(type=I3DMappingData)
     bpy.types.Scene.i3dio_merge_groups = CollectionProperty(type=I3DMergeGroup)
-    save_pre.append(prune_merge_groups)
     load_post.append(handle_old_merge_groups)
 
 def unregister():
     load_post.remove(handle_old_merge_groups)
-    save_pre.remove(prune_merge_groups)
     del bpy.types.Scene.i3dio_merge_groups
     del bpy.types.Object.i3d_mapping
     del bpy.types.Object.i3d_merge_group_index