Replaceable white mask

If you have a video that you first want it masked by a white background, and uncover the video as lines are drawn into it, you can use a jit.lcd with a white background, draw into it with black lines, and add that to your video. All the pixels that are white (255 255 255) in your jit.lcd matrix will be white in the summed output, and all the pixels that are black (0 0 0) in the jit.lcd will not affect the video.