sclass ImageSurfaceWithXMarkers extends ImageSurface {
  new L<Float> markers;
  Runnable onMarkersChanged;
  
  *(BufferedImage img, Collection<? extends Number> _markers) {
    super(img);
    addAll(this.markers, allToFloat(_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, new VF1<Pt> {
      Float marker;
      
      public void get(Pt p) {
        if (p == null) ret with marker = null;
        Pt pComponent = pointToComponentCoordinates(p.x, p.y);
        if (pointFarOutsideOfComponent(ImageSurfaceWithXMarkers.this, pComponent) || pointOutsideOfImage(image, p)) {
          if (marker != null) {
            markers.remove(marker);
            fireMarkersChanged();
            _print("Markers: " + l(markers));
          }
          ret with marker = null;
        }
        if (marker == null)
          marker = floatCloseTo(markers, p.x, 2/zoomX);
        Float m = marker;
        marker = (float) p.x;
        if (m == null) {
          markers.add(marker);
          _print("Markers: " + l(markers));
        } else
          replaceElementOnce(markers, m, marker);
        fireMarkersChanged();
      }
    });
  }
  
  void fireMarkersChanged {
    repaint();
    pcallF(onMarkersChanged);
  }
}