Move to MBScene._make_layers_integral() - Old MBScene.parseScene()/create_framelines()/update_framelines() is too fragile and inefficiently. - MBScene._make_layers_integral() is more robust that - separate logic into removing layer group nodes and adding layer group nodes - refactory code of create framelines and layers into methods - it make logic into layers - framelines and layers are incremental updated to avoid overhead of creating/destroying all framelines and layer objects.