I think it was around 1992/93, I was deep into graphics programming for games. The conventional way was to first draw the background and then draw everything on top of it (i.e. sprites etc.). However, this is wasting a lot of bandwidth since you can end up writing to the same video memory location multiple times.

I came up with an algorithm treating the each scan line of the screen as a binary tree which allowed me to keep track of which part of each scan line was already written to, meaning, I was able to build the screen up from front to back and visit each video memory location only once. So, on a 320x200 screen only ever 64000 bytes would be written to memory. With all the clipping etc. this was quite a complex beast and fully written in 286 assembler. In the end I think it made the overall graphics rendering about 20% to 25% faster.

Edit: I don't have the code anymore. I lost all my "floppy disks" in a house move... :(