sclass ImageSurface_HighlightRegion > ImageSurfaceMouseHandler is G2Drawable {

  settable RegionPainter regionPainter = new RegionBoundingBoxPainter;

  FastRegions_BWImage regions;

  int iHighlightedRegion;

  Pt lastPt;

  *(ImageSurface is) {

    if (containsInstance(is.tools, getClass())) ret;

    register(is);

    is.overlays.add(this);

  }

  public void close :: after {

    is.overlays.remove(this);

  }

  public void mouseMoved aka mouseEntered(MouseEvent e) {

    lastPt = getPt(e);

    update();

  }

  public void mouseExited(MouseEvent e) {

    lastPt = null;

    update();

  }

  int newRegion() {

    if (lastPt == null || regions == null) ret 0;

    ret regions.regionAt(lastPt.x, lastPt.y);

  }

  void update {

    int r = newRegion();

    if (iHighlightedRegion != r) {

      iHighlightedRegion = r;

      is.repaint();

    }

  }

  void setRegions(FastRegions_BWImage regions) {

    this.regions = regions;

    iHighlightedRegion = -abs(iHighlightedRegion);

    update();

  }

  public void drawOn(Graphics2D g) {

    if (iHighlightedRegion == 0 || regionPainter == null) ret;

    regionPainter.zoomX(is.getZoomX());

    regionPainter.zoomY(is.getZoomY());

    regionPainter.g(g); afterwards { regionPainter.g(null); }

    regionPainter.regions(regions).iRegion(iHighlightedRegion);

    regionPainter.drawRegion();

  }

}