Swing/AutoScroll のバックアップ(No.21)

class ViewportDragScrollListener extends MouseAdapter
                                 implements HierarchyListener {
  private static final int SPEED = 4;
  private static final int DELAY = 10;
  private final Cursor dc;
  private final Cursor hc = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
  private final Timer scroller;
  private final JComponent label;
  private Point startPt = new Point();
  private Point move    = new Point();

  public ViewportDragScrollListener(JComponent comp) {
    this.label = comp;
    this.dc = comp.getCursor();
    this.scroller = new Timer(DELAY, new ActionListener() {
      @Override public void actionPerformed(ActionEvent e) {
        Container c = SwingUtilities.getAncestorOfClass(JViewport.class, label);
        if (c instanceof JViewport.class) {
          JViewport vport = (JViewport) c;
          Point vp = vport.getViewPosition(); //= SwingUtilities.convertPoint(vport, 0, 0, label);
          vp.translate(move.x, move.y);
          label.scrollRectToVisible(new Rectangle(vp, vport.getSize())); //vport.setViewPosition(vp);
        }
      }
    });
  }
  @Override public void hierarchyChanged(HierarchyEvent e) {
    JComponent c = (JComponent)e.getSource();
    if((e.getChangeFlags() & HierarchyEvent.DISPLAYABILITY_CHANGED)!=0
       && !c.isDisplayable()) {
      scroller.stop();
    }
  }
  @Override public void mouseDragged(MouseEvent e) {
    JViewport vport = (JViewport)e.getSource();
    Point pt = e.getPoint();
    int dx = startPt.x - pt.x;
    int dy = startPt.y - pt.y;
    Point vp = vport.getViewPosition();
    vp.translate(dx, dy);
    label.scrollRectToVisible(new Rectangle(vp, vport.getSize()));
    move.setLocation(SPEED*dx, SPEED*dy);
    startPt.setLocation(pt);
  }
  @Override public void mousePressed(MouseEvent e) {
    e.getComponent().setCursor(hc); //label.setCursor(hc);
    startPt.setLocation(e.getPoint());
    move.setLocation(0, 0);
    scroller.stop();
  }
  @Override public void mouseReleased(MouseEvent e) {
    e.getComponent().setCursor(dc); //label.setCursor(dc);
    scroller.start();
  }
  @Override public void mouseExited(MouseEvent e) {
    e.getComponent().setCursor(dc); //label.setCursor(dc);
    move.setLocation(0, 0);
    scroller.stop();
  }
}