An Image inside a JScrollPane zooming by mouse wheel and panning by mouse click to drag

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

Code

class ZoomAndPanePanel extends JPanel {
  private final AffineTransform zoomTransform = new AffineTransform();
  private final transient Image img;
  private final Rectangle imgrect;
  private transient ZoomHandler handler;
  private transient DragScrollListener listener;

  protected ZoomAndPanePanel(Image img) {
    super();
    this.img = img;
    this.imgrect = new Rectangle(img.getWidth(this), img.getHeight(this));
  }
  @Override protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setPaint(new Color(0x55FF0000, true));
    Rectangle r = new Rectangle(500, 140, 150, 150);

    //use: AffineTransform#concatenate(...) and Graphics2D#setTransform(...)
    //https://docs.oracle.com/javase/8/docs/api/java/awt/geom/AffineTransform.html#concatenate-java.awt.geom.AffineTransform-
    //AffineTransform at = g2.getTransform();
    //at.concatenate(zoomTransform);
    //g2.setTransform(at);
    //g2.drawImage(img, 0, 0, this);
    //g2.fill(r);

    //or use: Graphics2D#drawImage(Image, AffineTransform, ImageObserver)
    //https://docs.oracle.com/javase/8/docs/api/java/awt/Graphics2D.html#drawImage-java.awt.Image-java.awt.geom.AffineTransform-java.awt.image.ImageObserver-
    g2.drawImage(img, zoomTransform, this); //or: g2.drawRenderedImage((RenderedImage) img, zoomTransform);
    g2.fill(zoomTransform.createTransformedShape(r));

    //BAD EXAMPLE
    //g2.setTransform(zoomTransform);
    //g2.drawImage(img, 0, 0, this);

    g2.dispose();
  }
  @Override public Dimension getPreferredSize() {
    Rectangle r = zoomTransform.createTransformedShape(imgrect).getBounds();
    return new Dimension(r.width, r.height);
  }
  @Override public void updateUI() {
    removeMouseListener(listener);
    removeMouseMotionListener(listener);
    removeMouseWheelListener(handler);
    super.updateUI();
    listener = new DragScrollListener();
    addMouseListener(listener);
    addMouseMotionListener(listener);
    handler = new ZoomHandler();
    addMouseWheelListener(handler);
  }

  protected class ZoomHandler extends MouseAdapter {
    private static final double ZOOM_MULTIPLICATION_FACTOR = 1.2;
    private static final int MIN_ZOOM = -10;
    private static final int MAX_ZOOM = 10;
    private static final int EXTENT = 1;
    private final BoundedRangeModel zoomRange = new DefaultBoundedRangeModel(
        0, EXTENT, MIN_ZOOM, MAX_ZOOM + EXTENT);
    @Override public void mouseWheelMoved(MouseWheelEvent e) {
      int dir = e.getWheelRotation();
      int z = zoomRange.getValue();
      zoomRange.setValue(z + EXTENT * (dir > 0 ? -1 : 1));
      if (z != zoomRange.getValue()) {
        Component c = e.getComponent();
        Container p = SwingUtilities.getAncestorOfClass(JViewport.class, c);
        if (p instanceof JViewport) {
          JViewport vport = (JViewport) p;
          Rectangle ovr = vport.getViewRect();
          double s = dir > 0 ? 1d / ZOOM_MULTIPLICATION_FACTOR : ZOOM_MULTIPLICATION_FACTOR;
          zoomTransform.scale(s, s);
          //double s = 1d + zoomRange.getValue() * .1;
          //zoomTransform.setToScale(s, s);
          Rectangle nvr = AffineTransform.getScaleInstance(s, s).createTransformedShape(ovr).getBounds();
          Point vp = nvr.getLocation();
          vp.translate((nvr.width - ovr.width) / 2, (nvr.height - ovr.height) / 2);
          vport.setViewPosition(vp);
          c.revalidate();
          c.repaint();
        }
      }
    }
  }
}

References

• An Image inside a JScrollPane zooming by mouse wheel and panning by mouse click to drag(Japanese)