- learning about Wu's anti-aliased circle algorithm and trying to implement it; Simon Alexander (salex on IRC) helped me out with that, but there's still a little glitch.
- reading the GIF documentation and creating a GIF writer in Common Lisp. The source for this part is available. (Do not try to dissuade me from using GIF, thanks.)
I made a silly little demo page; you can see it in action. The rounded corners are GIFs generated on the fly. It takes about 0.05 seconds to draw all four and save them to disk.