像素级透明和任意形状的窗口
像素级透明和像素级半透明类似，这种半透明模式主要用于任意形状窗口中的内容。
任意形状窗口是未加装饰的窗口，其外观与特定几何形状一致(如圆，圆角矩形等)，形状外的像素是透明的，在这些像素上点击才显示背景。
JDK 7通过向Window增加public void setShape(Shape shape)和public Shape getShape()方法支持像素级透明和任意形状的窗口，向前一个方法传递一个java.awt.Shape实例给当前窗口指定一个形状。
如果窗口处于全屏模式且传递来一个非空形状时，setShape()方法会抛出IllegalComponentStateException异常，如果不支持像素级透明且传递来一个非空形状时，抛出UnsupportedOperationException异常。
为了避免后一个异常，调用GraphicsDevice's isWindowTranslucencySupported()方法时，参数必须使用raphicsDevice.WindowTranslucency.PERPIXEL_TRANSPARENT，并检查返回的值，如下所示：
ge = GraphicsEnvironment.getLocalGraphicsEnvironment ();
if (!ge.getDefaultScreenDevice ().
isWindowTranslucencySupported (GraphicsDevice.WindowTranslucency.PERPIXEL_TRANSPARENT))
{
System.err.println ("per-pixel transparency isn't supported");
return;
}
我创建了一个PPTSWDemo程序演示像素级透明和任意形状的窗口，我们将清单2中显示出来的圆角矩形改成椭圆形状，清单3显示了这个程序的源代码。
清单3. 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);
}
}
在验证了支持像素级透明后，清单3执行setShape (new Ellipse2D.Float (0, 0, getWidth (), getHeight ()));将框架窗口改成椭圆形，效果如图3所示。
图 3 梯度式透明现在限制在椭圆范围内
遗憾的是，任意形状窗口的边缘有锯齿，也许等到JDK 7正式发布，使用像素级半透明和抗锯齿功能可以解决掉这个问题。
