Kinetic Scrolling JScrollPane

• download example.jar
• download src.zip
• repository

Code

class KineticScrollingListener2 extends MouseAdapter {
  private static final int SPEED = 4;
  private static final int DELAY = 10;
  private static final double D = 0.8;
  private final Cursor dc;
  private final Cursor hc = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
  private final javax.swing.Timer inside;
  private final javax.swing.Timer outside;
  private final JComponent label;
  private Point startPt = new Point();
  private Point delta   = new Point();
  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) {
    this.label = comp;
    this.dc = comp.getCursor();
    this.inside = new javax.swing.Timer(DELAY, new ActionListener() {
      @Override public void actionPerformed(ActionEvent e) {
        JViewport vport = (JViewport)label.getParent();
        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();
        }
      }
    });
    this.outside = new javax.swing.Timer(DELAY, new ActionListener() {
      @Override public void actionPerformed(ActionEvent e) {
        JViewport vport = (JViewport)label.getParent();
        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())*(1.0-D));
        if (vp.y+vport.getHeight()>label.getHeight())
          vp.y=(int)(vp.y-(vp.y+vport.getHeight()-label.getHeight())*(1.0-D));
        vport.setViewPosition(vp);
        if (isInside(vport, label)) outside.stop();
      }
    });
  }
  @Override public void mousePressed(MouseEvent e) {
    label.setCursor(hc);
    startPt.setLocation(e.getPoint());
    inside.stop();
    outside.stop();
  }
  @Override public void mouseDragged(MouseEvent e) {
    Point pt = e.getPoint();
    JViewport vport = (JViewport)label.getParent();
    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) {
    label.setCursor(dc);
    if (isInside((JViewport)label.getParent(), label)) {
      inside.start();
    } else {
      outside.start();
    }
  }
}

References

• Kinetic Scrolling JScrollPane(Japanese)
• sozai-free.com