Heh.. a friend of mine is taking a beginner's programming class in Processing. She wanted to make a "spotlight" effect where everything that the player's flashlight wasn't on was hidden in the dark. She knew in Flash it would be easy, just use a mask. There is no "draw everything but a circle" function in Processing, and masks are possible but difficult in it, and so last night I could only come up with lame half-solutions but this morning I GOT IT: an empty, giant circle drawn with an almost as giant heavy black border... the border effectively blocks out everything except what the spotlight is pointing at.
Sometimes you gotta think outside the box. Or, think inside the super-heavy bordered circle.
from Atari Force #2: