[math-fun] jaggies

http://gosper.org/jaggies.png is a 4x blowup of a detail of a Golly (Game of Life) screen, where each pixel is 2^24 x 2^24 cells. The diagonal line marked by arrows is a row of equally spaced gliders, (dx,dy) = (14412108,16685960). The gap at the green arrow is a legitimately missing glider, but every other dot on that line represents one glider. I.e., Golly darkens a pixel iff there's anything in the 2^24 square it represents. Note that dy>dx. Puzzle: How can the nonmonotonicity at the black arrow be anything but a display bug? (Does anybody remember BRMs and DDAs?) --rwg