def init_loader(engine):
        """
        Due to the feature of Panda3d, keep reference of loader in static variable
        """
        if engine.win is None:
            AssetLoader.logger.debug("Physics world mode")
            return
        assert engine.mode != RENDER_MODE_NONE
        AssetLoader.logger.debug("Onscreen/Offscreen mode, Render/Load Elements")
        AssetLoader.loader = engine.loader

        Due to the feature of Panda3d, keep reference of loader in static variable
        
metadrive/engine/asset_loader.py