- Simple Translucency
- Per-Pixel Translucency
- Per-Pixel Transparency and Shaped Windows
- Combining Translucency with Per-Pixel Transparency and Shaped Windows
- Conclusion
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Per-Pixel Transparency and Shaped Windows
Per-pixel transparency is similar to per-pixel translucency, except for each window pixel's opacity being restricted to 0.0 (transparent) or 1.0 (opaque). This translucency mode is used in the context of shaped windows.
A shaped window is an undecorated window whose appearance conforms to a specific shape (such as a circle or a rectangle with rounded corners). Pixels outside of the shape are transparent and reveal the background[md]clicking on these pixels achieves nothing.
JDK 7 supports per-pixel transparency and shaped windows by adding public void setShape(Shape shape) and public Shape getShape() methods to Window. Pass a java.awt.Shape instance to the former method to give the current window a specific shape.
The setShape() method throws IllegalComponentStateException if the window is in full-screen mode and a non-null shape is passed, and UnsupportedOperationException if per-pixel transparency isn't supported and a non-null shape is passed.
To avoid the latter exception, call GraphicsDevice's isWindowTranslucencySupported() method with argument GraphicsDevice.WindowTranslucency.PERPIXEL_TRANSPARENT, and check the return value, as follows:
GraphicsEnvironment ge;
ge = GraphicsEnvironment.getLocalGraphicsEnvironment ();
if (!ge.getDefaultScreenDevice ().
isWindowTranslucencySupported (GraphicsDevice.WindowTranslucency.PERPIXEL_TRANSPARENT))
{
System.err.println ("per-pixel transparency isn't supported");
return;
}
I've created a PPTSWDemo application that demonstrates per-pixel transparency and shaped windows by shaping Listing 2's rectangular gradient (without the gradient alpha values) into an ellipse. Listing 3 presents this application's source code.
Listing 3—PPTSWDemo.java
// PPTSWDemo.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 PPTSWDemo extends JFrame
{
public PPTSWDemo ()
{
super ("Per-Pixel Transparency and Shaped Window Demo");
setUndecorated (true); // Avoid decorated window artifacts.
JPanel gradPanel = new JPanel ()
{
// Solid white
Color colorA = new Color (255, 255, 255);
// Solid red
Color colorB = new Color (255, 0, 0);
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);
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_TRANSPARENT))
{
System.err.println ("per-pixel transparency isn't "+
"supported");
return;
}
new PPTSWDemo ();
}
};
EventQueue.invokeLater (r);
}
}
Sometime after verifying per-pixel transparency support, Listing 3 executes setShape (new Ellipse2D.Float (0, 0, getWidth (), getHeight ())); to shape the frame window into an ellipse. The resulting rounded window appears in Figure 3.
)
Figure 3 The gradient is now constrained to appear within the ellipse's interior.
Unfortunately, the shaped window has jagged edges. Perhaps the final release of JDK 7 will solve this problem by using per-pixel translucency and antialiasing. Or maybe it's possible to employ the idea presented in Chris Campbell's Java 2D Trickery: Soft Clipping blog post.