-do auxiliary rendering. With complex rendering hierarchies, these methods may
-be called multiple times for one frame, but it's guaranteed that no rendering
-will occur before a setup_frame call or after a finish_frame call.
+prepare textures or other data before actual rendering happens. With complex
+rendering graphs, these functions may be called multiple times for one frame,
+but it's guaranteed that no render() calls will occur before a setup_frame()
+call or after a finish_frame() call.