JScrollPaneでキネティックスクロール

class KineticScrollingListener2 extends MouseAdapter implements HierarchyListener {
  protected static final int SPEED = 4;
  protected static final int DELAY = 10;
  protected static final double D = .8;
  protected final JComponent label;
  protected final Point startPt = new Point();
  protected final Point delta = new Point();
  protected final Cursor dc;
  protected final Cursor hc = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
  protected final Timer inside = new Timer(DELAY, null);
  protected final Timer outside = new Timer(DELAY, null);

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

  protected KineticScrollingListener2(JComponent comp) {
    super();
    this.label = comp;
    this.dc = comp.getCursor();
    inside.addActionListener(e -> dragInside());
    outside.addActionListener(e -> dragOutside());
  }

  private void dragInside() {
    JViewport viewport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    Point vp = viewport.getViewPosition();
    // System.out.format("s: %s, %s%n", delta, vp);
    vp.translate(-delta.x, -delta.y);
    viewport.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 + viewport.getWidth() - label.getWidth() > 0) {
        delta.x = (int) (delta.x * D);
      }
      if (vp.y < 0 || vp.y + viewport.getHeight() - label.getHeight() > 0) {
        delta.y = (int) (delta.y * D);
      }
    } else {
      inside.stop();
      if (!isInside(viewport, label)) {
        outside.start();
      }
    }
  }

  private void dragOutside() {
    JViewport viewport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    Point vp = viewport.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 + viewport.getWidth() - label.getWidth() > 0) {
      vp.x = (int) (vp.x - (vp.x + viewport.getWidth() - label.getWidth()) * (1d - D));
    }
    if (vp.y + viewport.getHeight() > label.getHeight()) {
      vp.y = (int) (vp.y - (vp.y + viewport.getHeight() - label.getHeight()) * (1d - D));
    }
    viewport.setViewPosition(vp);
    if (isInside(viewport, label)) {
      outside.stop();
    }
  }

  @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 viewport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    Point vp = viewport.getViewPosition();
    vp.translate(startPt.x - pt.x, startPt.y - pt.y);
    viewport.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 viewport = (JViewport) SwingUtilities.getUnwrappedParent(label);
    if (isInside(viewport, 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();
    }
  }
}