Here’s an animation I made using the new AUMultiField masking call. This is an animated gif that I drew and saved one frame at a time.

I first drew a big white circle on a black background, and saved that in an AUField. That was my mask.

To draw each frame, I first drew the checkerboard full-screen and saved it in an AUField (I could have also drawn it into an offscreen PGraphics buffer). Then I cleared the screen to white, drew the outer circle, then the checkerboard with the mask, so it didn’t clobber my existing background and circle, and then finally drew the red dot on top.