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POHow do you implement position-sensitive zooming inside a JScrollPane?
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  1. POHow do you implement position-sensitive zooming inside a JScrollPane?
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    copied!<p>I am trying to implement position-sensitive zooming inside a <code>JScrollPane</code>. The <code>JScrollPane</code> contains a component with a customized <code>paint</code> that will draw itself inside whatever space it is allocated - so zooming is as easy as using a <code>MouseWheelListener</code> that resizes the inner component as required.</p> <p>But I also want zooming into (or out of) a point to keep that point as central as possible within the resulting zoomed-in (or -out) view (this is what I refer to as 'position-sensitive' zooming), similar to how zooming works in google maps. I am sure this has been done many times before - does anybody know the "right" way to do it under Java Swing?. Would it be better to play with <code>Graphic2D</code>'s transformations instead of using <code>JScrollPanes</code>?</p> <p>Sample code follows:</p> <pre><code>package test; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; import javax.swing.*; public class FPanel extends javax.swing.JPanel { private Dimension preferredSize = new Dimension(400, 400); private Rectangle2D[] rects = new Rectangle2D[50]; public static void main(String[] args) { JFrame jf = new JFrame("test"); jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jf.setSize(400, 400); jf.add(new JScrollPane(new FPanel())); jf.setVisible(true); } public FPanel() { // generate rectangles with pseudo-random coords for (int i=0; i&lt;rects.length; i++) { rects[i] = new Rectangle2D.Double( Math.random()*.8, Math.random()*.8, Math.random()*.2, Math.random()*.2); } // mouse listener to detect scrollwheel events addMouseWheelListener(new MouseWheelListener() { public void mouseWheelMoved(MouseWheelEvent e) { updatePreferredSize(e.getWheelRotation(), e.getPoint()); } }); } private void updatePreferredSize(int n, Point p) { double d = (double) n * 1.08; d = (n &gt; 0) ? 1 / d : -d; int w = (int) (getWidth() * d); int h = (int) (getHeight() * d); preferredSize.setSize(w, h); getParent().doLayout(); // Question: how do I keep 'p' centered in the resulting view? } public Dimension getPreferredSize() { return preferredSize; } private Rectangle2D r = new Rectangle2D.Float(); public void paint(Graphics g) { super.paint(g); g.setColor(Color.red); int w = getWidth(); int h = getHeight(); for (Rectangle2D rect : rects) { r.setRect(rect.getX() * w, rect.getY() * h, rect.getWidth() * w, rect.getHeight() * h); ((Graphics2D)g).draw(r); } } } </code></pre>
 

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