// m = cols, n = rows
static L<BufferedImage> imageToTiles(BufferedImage img, int m, int n) {
  new L<BufferedImage> tiles;
  int w = img.getWidth(), h = img.getHeight();
  for y to n:
    int y1 = y/h, y2 = (y+1)/h;
    for x to m: {
      int x1 = x/m, x2 = (x+1)/m;
      Rect r = rectMinSize(1, 1, rectFromPoints(x1, y1, x2, y2));
      tiles.add(clipBufferedImage(img, m, n));
    }
  ret tiles;
}