sclass CheckerBoard implements MakesBufferedImage {
  int w = 256, h = 256;
  double cols = 8, rows = 8;
  RGB color1 = RGB(Color.black), color2 = RGB(Color.white);
  
  public int getWidth() { ret w; }
  public int getHeight() { ret h; }
  
  public BufferedImage getBufferedImage() {
    ret toBufferedImage(rgbImageFromFunction(w, h, (x, y) -> {
      double col = doubleRatio(x, w)*cols/2;
      double row = doubleRatio(y, h)*rows/2;
      double xlow = frac(col), ylow = frac(row);
      ret xlow < .5 == ylow < .5 ? color1 : color2;
    }));
  }
}