Re: Scrolling around a panel with no components
In article
<4a344a30$0$32350$5a62ac22@per-qv1-newsreader-01.iinet.net.au>,
"Jarrick Chagma" <jarrick@large.com> wrote:
If a JPanel paints by drawing an off-screen buffered image and
contains no components, is it possible to scroll around the "content"
(i.e. what's in the buffer) by placing the panel in a JScrollPane?
In the code that follows I tried to do this but the scroll bars do
not appear. The code renders a red square that's bigger than the
size of the panel and I'd like to be able to use the scroll bars to
scroll around to see the parts of the square which are not initially
visible.
Could someone show me what I need to add to provide the scrolling
functionality I require?
Using setPreferredSize() will cause the scroll bars to appear, but I had
to eliminate the ComponentAdapter in order to see the right side of the
red square.
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Scrolling extends JFrame {
private static final int SIZE = 500;
private static final int INSET = 20;
private static final BufferedImage buffer = new
BufferedImage(SIZE, SIZE, BufferedImage.TYPE_INT_ARGB);
static {
final Graphics2D g2d = buffer.createGraphics();
g2d.setColor(Color.RED);
g2d.setStroke(new BasicStroke(4f));
final Rectangle r = new Rectangle(INSET, INSET,
buffer.getWidth() - 2 * INSET,
buffer.getHeight() - 2 * INSET);
g2d.draw(r);
g2d.setColor(Color.PINK);
g2d.fill(r);
g2d.dispose();
}
private class MyPanel extends JPanel {
public MyPanel() {
this.setPreferredSize(new Dimension(SIZE, SIZE));
}
@Override
public void paintComponent(final Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0, 0, this.getHeight(), this.getWidth());
g.drawImage(Scrolling.buffer, 0, 0, null);
}
}
public Scrolling() {
this.setLayout(new BorderLayout());
final MyPanel panel = new MyPanel();
final JScrollPane scrollPane = new JScrollPane(panel);
this.add(scrollPane, BorderLayout.CENTER);
this.pack();
this.setSize(SIZE - INSET, SIZE - INSET);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLocationRelativeTo(null);
}
public static void main(final String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
new Scrolling().setVisible(true);
}
});
}
}
--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>