sclass BWImage_FloodFillRegions extends FloodFillBWImage {

  Matrix<Region> matrix;

  bool verbose;

  new LinkedHashSet<Region> regions;

  class Region {

    new PointSetBitMatrix points;

    Rect boundingBox;

    float visualization = randomFloat(0.8f);

    void add aka addPoint(Pt p) {

      points.set(p, true);

      boundingBox = rectUnionWithPt(boundingBox, p);

    }

    int size() { ret points.nSetBits(); }

    Iterable<Pt> points() { ret points.points; }

    toString { ret "Region with " + nPixels(size()) + " within " + boundingBox; }

    IBWImage asImage() {

      ret iBWImageFromFunction((x, y) -> points.get(pt(x, y)) ? 0 : 1, w, h);

    }

  }

  void addedPoint(Pt p) {

    new Region r;

    r.add(p);

    matrix.put(p, r);

    print("addedPoint " + p + ": " + r);

    regions.add(r);

  }

  void visited(Pt p) {

    if (verbose) print("Visited point: " + p);

  }

  *(IBWImage *img) {

    super(img); 

    matrix = new ArrayMatrix(w, h);

  }

  bool isConnectable(Pt a, Pt b) {

    float brightnessA = img.getFloatPixel(a);

    float brightnessB = img.getFloatPixel(b);

    ret abs(brightnessA-brightnessB) <= tolerance;

  }

  void createBridge(Pt a, Pt b) {

    var regionA = matrix.get(a);

    var regionB = matrix.get(b);

    if (regionA == regionB) ret;

    if (regionB == null) fail("regionB = null: " + b);

    for (p : regionB.points()) {

      matrix.set(p, regionA);

      regionA.addPoint(p);

    }

    regions.remove(regionB);

  }

  void dropOnePixelRegions {

    filterCollectionInPlace(regions, r -> {

      if (r.size() <= 1) {

        removeFromMatrix(r);

        false;

      }

      true;

    });

  }

  void removeFromMatrix(Region r) {

    for (Pt p : r.points.points) matrix.set(p, null);

  }

  IBWImage regionsImage() {

    ret iBWImageFromFunction((x, y) -> {

      var region = matrix.get(x, y);

      ret region == null ? 1 : region.visualization;

    }, w, h);

  }

  void run { doAllPoints(); }

}