sclass ImageSurfaceWithXMarkers extends ImageSurface {
  new L<Float> markers;
  
  *(BufferedImage img, Collection<Float> _markers) {
    super(img);
    addAll(this.markers, _markers);
    overlay = voidfunc(Graphics2D g) {
      g.setColor(Color.red);
      for (float x : markers) {
        Pt p = pointToComponentCoordinates(x, 0);
        g.drawLine(p.x, 0, p.x, getHeight()-1);
      }
    };
    disableImageSurfaceSelector(this);
    imageSurfaceOnMouseDrag(this, voidfunc(Pt p) {
      //_print("p=" + p);
      Float marker = floatCloseTo(markers, p.x, 2/zoomX);
      if (marker == null)
        markers.add((float) p.x);
      else
        replaceElement(markers, marker, (float) p.x);
      repaint();
    });
  }
}