Register a function to be called when a scene unload started. This is
before the object deletion and renderer destruction. It is safe to
manipulate these. It is not safe to release resources as other
callbacks might do operations on objects or the scene.
Register a function to be called when a scene unload started. This is before the object deletion and renderer destruction. It is safe to manipulate these. It is not safe to release resources as other callbacks might do operations on objects or the scene.