JScrollPaneでキネティックスクロール

class KineticScrollingListener2 extends MouseAdapter implements HierarchyListener {
  private static final int SPEED = 4;
  private static final int DELAY = 10;
  private static final double D = 0.8;
  private final JComponent label;
  private final Point startPt = new Point();
  private final Point delta = new Point();
  private final Cursor dc;
  private final Cursor hc = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
  private final Timer inside = new Timer(DELAY, new ActionListener() {
    @Override public void actionPerformed(ActionEvent e) {
      JViewport vport = (JViewport) SwingUtilities.getUnwrappedParent(label);
      Point vp = vport.getViewPosition();
      // System.out.format("s: %s, %s%n", delta, vp);
      vp.translate(-delta.x, -delta.y);
      vport.setViewPosition(vp);
      if (Math.abs(delta.x) > 0 || Math.abs(delta.y) > 0) {
        delta.setLocation((int) (delta.x * D), (int) (delta.y * D));
        // Outside
        if (vp.x < 0 || vp.x + vport.getWidth() - label.getWidth() > 0) {
          delta.x = (int) (delta.x * D);
        }
        if (vp.y < 0 || vp.y + vport.getHeight() - label.getHeight() > 0) {
          delta.y = (int) (delta.y * D);
        }
      } else {
        inside.stop();
        if (!isInside(vport, label)) {
          outside.start();
        }
      }
    }
  });
  private final Timer outside = new Timer(DELAY, new ActionListener() {
    @Override public void actionPerformed(ActionEvent e) {
      JViewport vport = (JViewport) SwingUtilities.getUnwrappedParent(label);
      Point vp = vport.getViewPosition();
      // System.out.format("r: %s%n", vp);
      if (vp.x < 0) {
        vp.x = (int) (vp.x * D);
      }
      if (vp.y < 0) {
        vp.y = (int) (vp.y * D);
      }
      if (vp.x + vport.getWidth() - label.getWidth() > 0) {
        vp.x = (int) (vp.x - (vp.x + vport.getWidth() - label.getWidth()) * (1d - D));
      }
      if (vp.y + vport.getHeight() > label.getHeight()) {
        vp.y = (int) (vp.y - (vp.y + vport.getHeight() - label.getHeight()) * (1d - D));
      }
      vport.setViewPosition(vp);
      if (isInside(vport, label)) {
        outside.stop();
      }
    }
  });

  private static boolean isInside(JViewport vport, JComponent comp) {
    Point vp = vport.getViewPosition();
    return vp.x >= 0 && vp.x + vport.getWidth()  - comp.getWidth()  <= 0
        && vp.y >= 0 && vp.y + vport.getHeight() - comp.getHeight() <= 0;
  }

  public KineticScrollingListener2(JComponent comp) {
    super();
    this.label = comp;
    this.dc = comp.getCursor();
  }

  @Override public void mousePressed(MouseEvent e) {
    e.getComponent().setCursor(hc);
    startPt.setLocation(e.getPoint());
    inside.stop();
    outside.stop();
  }

  @Override public void mouseDragged(MouseEvent e) {
    Point pt = e.getPoint();
    JViewport vport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    Point vp = vport.getViewPosition();
    vp.translate(startPt.x - pt.x, startPt.y - pt.y);
    vport.setViewPosition(vp);
    delta.setLocation(SPEED * (pt.x - startPt.x), SPEED * (pt.y - startPt.y));
    startPt.setLocation(pt);
  }

  @Override public void mouseReleased(MouseEvent e) {
    e.getComponent().setCursor(dc);
    JViewport vport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    if (isInside(vport, label)) {
      inside.start();
    } else {
      outside.start();
    }
  }

  @Override public void hierarchyChanged(HierarchyEvent e) {
    Component c = e.getComponent();
    if ((e.getChangeFlags() & HierarchyEvent.DISPLAYABILITY_CHANGED) != 0
        && !c.isDisplayable()) {
      inside.stop();
      outside.stop();
    }
  }
}