In Donald Knuth's TAoCP Pre-Fascicle 1a: Bitwise Tricks and Techniques, he shows a patchwork quilt defined by f(x, y) = ((x ^ y) & ((y - 350) >> 3)) ** 2, designed by D. Sleator in 1976. I wanted to recreate this quilt myself using Ruby. The following program generates a PNG file of the "quilt."
def f(x, y)
( (x ^ y) & ((y - 350) >> 3) ) ** 2
canvas = PNG::Canvas.new(500, 500)
0.upto(499) do |y|
0.upto(499) do |x|
canvas[x, 499 - y] = ((f(x, y) >> 12) & 1) == 1 ? PNG::Color::Black : PNG::Color::White
png = PNG.new(canvas)