updatePixels

  if (tl != null && br != null) {
    loadPixels();
    for (int x = (int)tl.x; x <= br.x; x++) {
      pixels[(int)tl.y*width + x] = color(255, 100, 0);
      pixels[(int)br.y*width + x] = color(255, 100, 0);
    }
    for (int y = (int)tl.y; y <= br.y; y++) {
      pixels[y*width + (int)tl.x] = color(255, 100, 0);
      pixels[y*width + (int)br.x] = color(255, 100, 0);
    }
    updatePixels();
  }