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() {
    if (!iterator.hasNext())
      false;
    int pixel = iterator.nextIndex();
    if (regionMaker.regionMatrix[pixel] == 0) {
      regionMaker.runner = pixel;
      regionMaker.makeRegion();
    }
    true;
  }
  
  // null if there are no more regions
  public IImageRegion<Img> nextRegion() {
    var regionMatrix = regionMaker.regionMatrix;
    while (iterator.hasNext()) {
      int pixel = iterator.nextIndex();
      if (regionMatrix[pixel] == 0) {
        regionMaker.runner = pixel;
        ret regionMaker.getRegion(regionMaker.makeRegion());
      }
    }
    null;
  }
}