Swing/ZoomingAndPanning のバックアップ(No.12)

class ZoomAndPanHandler extends MouseAdapter {
  private static final double ZOOM_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);
  private final AffineTransform coordAndZoomAtf = new AffineTransform();
  private final Point2D dragStartPoint = new Point();

  @Override public void mousePressed(MouseEvent e) {
    dragStartPoint.setLocation(e.getPoint());
  }

  @Override public void mouseDragged(MouseEvent e) {
    Point2D dragEndPoint = e.getPoint();
    Point2D dragStart = transformPoint(dragStartPoint);
    Point2D dragEnd = transformPoint(dragEndPoint);
    coordAndZoomAtf.translate(
        dragEnd.getX() - dragStart.getX(), dragEnd.getY() - dragStart.getY());
    dragStartPoint.setLocation(dragEndPoint);
    e.getComponent().repaint();
  }

  @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()) {
      return;
    }
    Component c = e.getComponent();
    Rectangle r = c.getBounds();
    Point2D p = new Point2D.Double(r.getCenterX(), r.getCenterY());
    Point2D p1 = transformPoint(p);
    double scale = dir > 0 ? 1 / ZOOM_FACTOR : ZOOM_FACTOR;
    coordAndZoomAtf.scale(scale, scale);
    Point2D p2 = transformPoint(p);
    coordAndZoomAtf.translate(p2.getX() - p1.getX(), p2.getY() - p1.getY());
    c.repaint();
  }

  // https://community.oracle.com/thread/1263955
  // How to implement Zoom & Pan in Java using Graphics2D
  private Point2D transformPoint(Point2D p1) {
    AffineTransform inverse = coordAndZoomAtf;
    boolean hasInverse = coordAndZoomAtf.getDeterminant() != 0d;
    if (hasInverse) {
      try {
        inverse = coordAndZoomAtf.createInverse();
      } catch (NoninvertibleTransformException ex) {
        // should never happen
        assert false;
      }
    }
    Point2D p2 = new Point();
    inverse.transform(p1, p2);
    return p2;
  }

  public AffineTransform getCoordAndZoomTransform() {
    return coordAndZoomAtf;
  }
}