sclass ImageSurfaceDragger extends MouseAdapter {
  sbool debug = true;
  ImageSurface is;
  Point start, startScroll;
  int dx, dy;

  *(ImageSurface *is) {
    if (containsInstance(is.tools, ImageSurfaceDragger)) ret;
    print("Loading ImageSurfaceDragger");
    ifclass ImageSurfaceSelector
      for (ImageSurfaceSelector s : collectInstances(is.tools, ImageSurfaceSelector)) {
        is.removeMouseListener(s);
        is.removeMouseMotionListener(this);
        is.tools.remove(s);
      }
    endif
    is.tools.add(this);
    is.addMouseListener(this);
    is.addMouseMotionListener(this);
  }

  public void mousePressed(MouseEvent e) {
    JScrollPane sp = enclosingScrollPane(is);
    if (sp == null) ret;
    if (e.getButton() == MouseEvent.BUTTON1) {
      start = e.getLocationOnScreen();
      startScroll = new Point(
        sp.getHorizontalScrollBar().getValue(),
        sp.getVerticalScrollBar().getValue());
    }
  }

  public void mouseDragged(MouseEvent e) {
    JScrollPane sp = enclosingScrollPane(is);
    if (sp == null) ret;
    Point p = e.getLocationOnScreen();
    //if (debug) print("ImageSurfaceDragger: drag " + p.x + "/" + p.y);
    sp.getHorizontalScrollBar().setValue(-(p.x-start.x)+startScroll.x);
    sp.getVerticalScrollBar().setValue(-(p.y-start.y)+startScroll.y);
  }

  public void mouseReleased(MouseEvent e) {
    mouseDragged(e);
  }
}