A long time ago, I also made these kinds of programs. That was on a PET 2001, and I didn't have the luxury of bitmaps back then. I would use the PET's graphic characters as 'actors', and POKE them to the video memory. It started with simple balls, but soon my 'actors' grew into sprites made up from multiple characters (with a square, a few line graphics and a ball you could make a little fellow). POKEing all these characters from BASIC became a bit slow, and that was the moment I started learning machine language (<i>necessity is the mother of invention</i>), and from then on I wrote my PET games in 6502 assembly. That made them blindingly fast! (And very prone to crashing, too ;-)