Custom generator of previews. Custom code to generate previews. Please check "file_dialog/thumbnail_size" in EditorSettings to find out the right size to do previews at. Generate a preview from a given resource with the specified size. This must always be implemented. Returning an empty texture is an OK way to fail and let another generator take care. Care must be taken because this function is always called from a thread (not the main thread). Generate a preview directly from a path with the specified size. Implementing this is optional, as default code will load and call [method generate]. Returning an empty texture is an OK way to fail and let another generator take care. Care must be taken because this function is always called from a thread (not the main thread). Returns if your generator supports this resource type.