sclass G22ColorWalker > G22Walker {
  // the ideal image it is looking for (set/get)
  int[] rememberedImage; // size visionW*visionH
  
  void move(IRGBImage image) {
    stuck = false;
    guessWork = 0;
    
    // How far can I move until I hit the image's borders
    Rect movement1 = rectFromPoints(visionW/2, visionH/2,
      image.getWidth()-(visionW+1)/2, (visionH+1)/2);
    
    // How far can I walk in one frame
    Rect movement2 = rectAroundPt(position, range*2+1);
    
    Rect movement = intersectRects(movement1, movement2);
    if (empty(movement)) ret with set stuck;
    
    printVars(+movement, +movement1, +movement2);
    
    if (rememberedImage == null)
      ret with rememberImage(image);
    
    Rect r = window_uncropped();
    
    new MultiBest<Pt> bestPositions;
    
    int mx1 = movement.x1(), mx2 = movement.x2();
    int my1 = movement.y1(), my2 = movement.y2();
    for (int y = my1; y < my2; y++)
      for (int x = mx1; x < mx2; x++) {
        var newPos = pt(x, y);
        bestPositions.put(newPos, scorePosition(newPos, image));
      }
    var best = bestPositions!;
    guessWork = l(best);
    position = random(best);
    
    // It's actually a question how often we grab a fresh image.
    // For now, every time.
    rememberImage(image);
  }
  
  // only works when we already have a rememberedImage
  double scorePosition(Pt pos, IBWImage image) {
    int vx = pos.x-visionW, vy = pos.y-visionH, i = 0;
    int diff = 0;
    for y to visionH:
      for x to visionW:
        diff += colorDiff(rememberedImage[i++], image.getIntPixel(vx+x, vy+y));
    ret -diff;
  }
  
  void rememberImage(IRGBImage image) {
    if (rememberedImage == null)
      rememberedImage = new int[visionW*visionH];
      
    int vx = visionX1(), vy = visionY1(), i = 0;
    for y to visionH:
      for x to visionW:
        rememberedImage[i++] = image.getIntPixel(vx+x, vy+y);
  }
}