yea i tried that, it didnt exactly give me the behavior i was looking for.

i really think the best way to do it would be to draw 2 images on top of each other. the one in the forground would be the one i could draw onto, and the one in the background would just be there to fill in the spots that i erase from the forground picture. does this make sense? how can i go about drawing 2 images like this?