This is meant to be multi-colored volume-rendered god rays. Although I certainly didn’t know those fancy words at the time! It uses software rasterization and is written in SDL. At this point it should mostly just have looked black but I think that a lot of the pixels had a whiteness value that overflowed, and the pattern of overflowings is what you see here. I am pretty sure that the value that the whiteness each pixel was getting was basically coming from the number of rays originating from the center that passed through it?