Another option would be to capture a screenshot of your panel and then let it paint itself with an increasing alpha composite.
Here is a small demo of that (although I am not sure this is really clean):
import java.awt.AlphaComposite;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.net.MalformedURLException;
import java.net.URL;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class TestFading {
private static class FadingPanel extends JPanel {
private BufferedImage buffer;
private boolean isFading = false;
private long start;
private float alpha = 1.0f;
@Override
public void paint(Graphics g) {
if (isFading) {// During fading, we prevent child components from being painted
g.clearRect(0, 0, getWidth(), getHeight());
((Graphics2D) g).setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
g.drawImage(buffer, 0, 0, this);// We only draw an image of them with an alpha
} else {
super.paint(g);
}
}
public void fade(int time) {
start = System.currentTimeMillis();
buffer = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
this.print(buffer.getGraphics());// Draw the current components on the buffer
isFading = true;
final int timeInMillis = time * 1000;
final Timer t = new Timer(50, null);
t.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
long elapsed = System.currentTimeMillis() - start;
if (elapsed > timeInMillis) {
start = 0;
isFading = false;
buffer = null;
repaint();
t.stop();
} else {
alpha = 1.0f - (float) elapsed / timeInMillis;
repaint();
}
}
});
t.start();
}
}
protected void initUI() throws MalformedURLException {
JFrame frame = new JFrame(TestFading.class.getSimpleName());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final FadingPanel panel = new FadingPanel();
JTextField textfield = new JTextField(60);
JLabel image = new JLabel(new ImageIcon(new URL("http://helios.gsfc.nasa.gov/image_mag_stamp.jpg")));
JButton button = new JButton("Fade");
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
// I use an invoke later to allow the button to release itself
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
panel.fade(5);// Fade the panel in 5s.
}
});
}
});
panel.add(textfield);
panel.add(image);
panel.add(button);
frame.add(panel);
frame.setSize(400, 300);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
try {
new TestFading().initUI();
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
});
}
}
