Patchwork quilt pattern in Ruby (from Knuth TAoCP 4 - 7.1.3)
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."
1 2 require 'rubygems' 3 require 'png' 4 5 def f(x, y) 6 ( (x ^ y) & ((y - 350) >> 3) ) ** 2 7 end 8 9 canvas = PNG::Canvas.new(500, 500) 10 11 0.upto(499) do |y| 12 0.upto(499) do |x| 13 canvas[x, 499 - y] = ((f(x, y) >> 12) & 1) == 1 ? PNG::Color::Black : PNG::Color::White 14 end 15 end 16 17 png = PNG.new(canvas) 18 png.save 'pattern.png'
