Advice for JPanel transparency idea

Question

Hi!
I've spent all day reading about the CardLayout and JLayeredPane and am confused as to which route to take.
Here's what I'm planning to build:
- One frame containing three panels.
- Each panel holds an invididual image and and stretches to the extents of the frame, thus the panels sit on top of each other.
- I would like to be able to change the order of the panels
- Here's the killer: I'd like to change the transparancy of the top panel (either partially or completely) so that I can peer through to the panel below.
Any advice would be appreciated. Many thanks...

Answer 1

To summarise (thanks J_Rooze for advice):
- Setting the AlphaComposite value before calling super.paintComponent(g2) will change the transparency of the whole panel.
- Performance will drop in the order of ~40%, but using J_Rooze's suggestion to force the OpenGL rendering pipeline (above) completely remedies this (is there a similar hack for java3D?? :-).
- Using these panels with JLayeredPane worked completely for my spec (top post).
- I also tried them in CardLayout, however, whilst I could get the top panel to go transparent the underneath panel would not show through. This might not necessarily be a problem for other specs.
- Panels should be .setOpaque(false) to eliminate crazy phasing effects.
Here's my working code for reference:
import java.awt.*;
import javax.swing.JPanel;
public class DisplayPanel extends JPanel{
     private boolean antiAlias;
     private float alpha = 1.0f;
     public DisplayPanel(boolean setAntiAlias) {
          antiAlias = setAntiAlias;
          this.setOpaque(false);
     public void setAlpha(float a) {
          alpha = a;
          if (alpha > 1) alpha = 1.0f;
          if (alpha < 0) alpha = 0.0f;
          repaint();
     public float getAlpha() {
          return alpha;
     protected void paintComponent(Graphics g) {
          Graphics2D g2 = (Graphics2D)g;
          AlphaComposite ac = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, getAlpha());
          g2.setComposite(ac);
          super.paintComponent(g2);
          // for speed
          g2.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_SPEED);
          g2.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_SPEED);
          if (antiAlias) g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
          //draw commands go here
}Edited by: .eD on May 7, 2008 4:46 AM