1. Control is passed back by calling callback functions set up by the programmer on specific events. This is set up by registering the callbacks to events during initialization (eg, glutDisplayFunc). 2. Sets RGBA color instead of indexed color and sets double-buffering instead of single. 3. glOrtho sets the view volume to range from (0,0,-1) to (1,1,1). glViewport sets the OpenGL rendering area in the window to range from (0,0) to (w,h).