import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.RenderingHints;
import java.awt.Transparency;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class CircleTest {
public static void main(String[] args) {
JFrame f = new JFrame();
JPanel p = new JPanel(){
protected void paintComponent(Graphics g)
{
// Clear the background to black
g.setColor(Color.BLACK);
g.fillRect(0, 0, getWidth(), getHeight());
// Create a translucent intermediate image in which we can perform
// the soft clipping
GraphicsConfiguration gc = getGraphicsConfiguration();
BufferedImage img = gc.createCompatibleImage(getWidth(), getHeight(), Transparency.TRANSLUCENT);
Graphics2D g2 = img.createGraphics();
// Clear the image so all pixels have zero alpha
g2.setComposite(AlphaComposite.Clear);
g2.fillRect(0, 0, getWidth(), getHeight());
// Render our clip shape into the image. Note that we enable
// antialiasing to achieve the soft clipping effect. Try
// commenting out the line that enables antialiasing, and
// you will see that you end up with the usual hard clipping.
g2.setComposite(AlphaComposite.Src);
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(Color.WHITE);
g2.fillOval(getWidth()/4, getHeight()/4, getWidth()/2, getHeight()/2);
// Here's the trick... We use SrcAtop, which effectively uses the
// alpha value as a coverage value for each pixel stored in the
// destination. For the areas outside our clip shape, the destination
// alpha will be zero, so nothing is rendered in those areas. For
// the areas inside our clip shape, the destination alpha will be fully
// opaque, so the full color is rendered. At the edges, the original
// antialiasing is carried over to give us the desired soft clipping
// effect.
g2.setComposite(AlphaComposite.SrcAtop);
g2.setPaint(new GradientPaint(0, 0, Color.RED, 0, getHeight(), Color.YELLOW));
g2.fillRect(0, 0, getWidth(), getHeight());
g2.dispose();
// Copy our intermediate image to the screen
g.drawImage(img, 0, 0, null);
};
};
f.add(p);
f.pack();
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
