sclass AbstractFastRegions_ShuffledScan<Img extends WidthAndHeight> is Steppable {
  AbstractFastRegions<Img> regionMaker;
  WeightlessShuffledIterator iterator;
  
  *(AbstractFastRegions<Img> *regionMaker) {
    regionMaker.init();
    iterator = new WeightlessShuffledIterator(regionMaker.size);
  }
  
  public bool step() {
    ret findNextRegion() > 0;
  }
  
  int findNextRegion() {
    var regionMatrix = regionMaker.regionMatrix;
    while (iterator.hasNext()) {
      int pixel = iterator.nextIndex();
      if (regionMatrix[pixel] == 0) {
        regionMaker.runner = pixel;
        ret regionMaker.getRegion(regionMaker.makeRegion());
      }
    }
    ret 0;
  }
  
  // null if there are no more regions
  IImageRegion<Img> nextRegion() {
    int iRegion = findNextRegion();
    ret iRegion > 0 ? regionMaker.getRegion(iRegion) : null;
  }
}