static BufferedImage imageFromFunction(int w, int h default w, IF2_Int f) {
  int[] pixels = new[w*h];
  int i = 0;
  for y to h:
    for x to w:
      pixels[i++] = f.get(x, y);
  ret intArrayToBufferedImage(pixels, w, h);
}

Began life as a copy of #1032071