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  1. Simple Translucency
  2. Per-Pixel Translucency
  3. Per-Pixel Transparency and Shaped Windows
  4. Combining Translucency with Per-Pixel Transparency and Shaped Windows
  5. Conclusion
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Combining Translucency with Per-Pixel Transparency and Shaped Windows

Combining Translucency with Per-Pixel Transparency and Shaped Windows

You can combine per-pixel (or even simple) translucency with per-pixel transparency to achieve a translucent shaped window. For proof, check out Listing 4, whose CTSWDemo application source code extends the previous application to also include per-pixel translucency.

Listing 4—CTSWDemo.java

// CTSWDemo.java
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class CTSWDemo extends JFrame
{
   public CTSWDemo ()
   {
      super ("Combined Translucency with Per-Pixel Transparency and Shaped "+
             "Window Demo");
      setUndecorated (true); // Avoid decorated window artifacts.
      JPanel gradPanel = new JPanel ()
                         {
                             Color colorA = new Color (255, 0, 0, 0);
                             Color colorB = new Color (255, 0, 0, 255);
                             protected void paintComponent (Graphics g)
                             {
                                 Graphics2D g2d = (Graphics2D) g;
                                 GradientPaint gp;
                                 gp = new GradientPaint (0.0f, 0.0f, colorA,
                                                         0.0f, getHeight (),
                                                         colorB, true);
                                 g2d.setPaint (gp);
                                 g2d.fillRect (0, 0, getWidth (),
                                               getHeight ());
                                 
                             }
                         };
      gradPanel.setPreferredSize (new Dimension (300, 200));
      gradPanel.setLayout (new BoxLayout (gradPanel, BoxLayout.Y_AXIS));
      JButton btnClose = new JButton ("Close");
      ActionListener al;
      al = new ActionListener ()
           {
               public void actionPerformed (ActionEvent ae)
               {
                  System.exit (0);
               }
           };
      btnClose.addActionListener (al);
      btnClose.setAlignmentX (0.5f);
      gradPanel.add (Box.createVerticalGlue ());
      gradPanel.add (btnClose);
      gradPanel.add (Box.createVerticalGlue ());
      setContentPane (gradPanel);
      if (!getGraphicsConfiguration ().isTranslucencyCapable ())
      {
          System.err.println ("per-pixel translucency not in effect for this "+
                              "graphics configuration");
          System.exit (0);
      }
      setBackground (new Color (0, 0, 0, 0)); // Achieve per-pixel
                                              // translucency.
      pack ();
      setShape (new Ellipse2D.Float (0, 0, getWidth (), getHeight ()));
      setLocationRelativeTo (null);
      setVisible (true);
   }
   public static void main (String [] args)
   {
      Runnable r;
      r = new Runnable ()
          {
              public void run ()
              {
                 GraphicsEnvironment ge;
                 ge = GraphicsEnvironment.getLocalGraphicsEnvironment ();
                 if (!ge.getDefaultScreenDevice ().
                         isWindowTranslucencySupported
                           (GraphicsDevice.WindowTranslucency.
                                           PERPIXEL_TRANSLUCENT))
                 {
                     System.err.println ("per-pixel translucency isn't "+
                                         "supported");
                     return;
                 }
                 if (!ge.getDefaultScreenDevice ().
                         isWindowTranslucencySupported
                           (GraphicsDevice.WindowTranslucency.
                                           PERPIXEL_TRANSPARENT))
                 {
                     System.err.println ("per-pixel transparency isn't "+
                                         "supported");
                     return;
                 }
                 new CTSWDemo ();
              }
          };
      EventQueue.invokeLater (r);
   }
}

Listing 4's panel gradient code once again employs alpha values when creating the pair of Color objects. As Figure 4 shows, however, the translucent red gradient now occupies an elliptical shape portion of the undecorated window instead of the entire window.

Figure 4 The setBackground() method call allows the ellipse-shaped window's interior to be rendered with the gradient of red translucency.

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