A role for objects to draw on top of a video. Requires a process_video_overlay() method, which will be passed the UAV::Pilot::SDL::Window object that the video is drawing to.

Where $video is an UAV::Pilot::SDL::Video object, you can set an $overlay object with:

    $video->register_video_overlay( $overlay );

NOTE: This is still experimental. Lines tend to flicker and show up as black. This is probably due to the SDL YUV hardware overlay.