Hey, first of all, it's awesome to hear that. I miss screen savers and procedural animation so much... I mean, I used to zone out on them for hours, and try to write my own as a kid. It was a lot of fun. I realize the world has no need for them anymore, but I still
like them. I'm not sure how we got to a point where there's only one basic screen saver for the Mac and it's almost impossible to find anything else.
I hadn't heard of hopalong fractals, but this code implements something very similar. Conceptually, if you scan the whole image space at each iteration and, for each lit pixel you light up another random pixel at half the brightness within a certain radius, things will begin to trend in one direction. Because if the first one you light happens to be off to the left, then there's double the probability that the next will be at least that far to the left, and then the leftward spread becomes exponentially more likely in the following iterations. I haven't actually encountered spiral arms in this, but maybe following hopalongs will be my next saver ;) There's a lot you can do with a little code here. You can warp the space you want to light up, or over/under light certain things, re-amplify, or run a fader on the entire screen in a few bytes. The possibilities are endless. But it's kind of like...how do I make a thing that looks like that? The fun part, for me, of making a screen saver or any procedural art is cooking with very few ingredients and lots of limitations.