(FULL SOURCE CODE: ONLINE ONLY) AlphaCompositeRules.Java.

• By Vincent J. Hardy
• June 13, 2000

import java.awt.*;
import java.awt.image.*;
import java.awt.geom.*;
import java.awt.event.*;
import java.io.*;

import javax.swing.*;

/**
 * Illustrates the use of the AlphaComposite class by showing the output created
 * with different settings for that class's constructors. The code shows the result
 * for the different Porter-Duff composition rules, with different alpha values.
 * 
 * This example uses offscreen rendering
 *
 * @author    Vincent Hardy
 * @version   1.0, 12/30/1998
 */
public class AlphaCompositeRules extends JComponent{
  // List of each AlphaCompositeRule, using two different alpha values
  static AlphaComposite alphaComposites[] = {
    AlphaComposite.Clear,
    AlphaComposite.getInstance(AlphaComposite.CLEAR, .5f),
    AlphaComposite.DstIn,
    AlphaComposite.getInstance(AlphaComposite.DST_IN, .5f),
    AlphaComposite.DstOut,
    AlphaComposite.getInstance(AlphaComposite.DST_OUT, .5f),
    AlphaComposite.DstOver,
    AlphaComposite.getInstance(AlphaComposite.DST_OVER, .5f),
    AlphaComposite.Src,
    AlphaComposite.getInstance(AlphaComposite.SRC, .5f),
    AlphaComposite.SrcIn,
    AlphaComposite.getInstance(AlphaComposite.SRC_IN, .5f),
    AlphaComposite.SrcOut,
    AlphaComposite.getInstance(AlphaComposite.SRC_OUT, .5f),
    AlphaComposite.SrcOver,
    AlphaComposite.getInstance(AlphaComposite.SRC_OVER, .5f),
  };

  BufferedImage buf;
  Shape blueDisc, redDisc;
  Rectangle bounds;

  public AlphaCompositeRules(){
		redDisc = new Ellipse2D.Float(1, 2, 7, 7);
		blueDisc = new Ellipse2D.Float(5, 2, 7, 7);

		AffineTransform scale = AffineTransform.getScaleInstance(10, 10);
		redDisc  = scale.createTransformedShape(redDisc);
		blueDisc = scale.createTransformedShape(blueDisc);

    bounds = redDisc.getBounds();
    bounds.add(blueDisc.getBounds());
    bounds.width += 30;
    bounds.height += 10;
    buf = new BufferedImage((bounds.x + bounds.width)*2,
			    (bounds.y + bounds.height)*alphaComposites.length/2,
			    BufferedImage.TYPE_INT_ARGB_PRE);
    Graphics2D g = buf.createGraphics();
    setPreferredSize(new Dimension(buf.getWidth(), buf.getHeight()));

    paintGraphics(g);
  }

	public Dimension getPreferredSize(){
		return new Dimension(buf.getWidth(), buf.getHeight());
	}

  public void paintGraphics(Graphics2D g){
    // g.scale(.25, .25);
    g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    // 
    // Iterate through the list of alphaComposites
    //
    Color red = new Color(200, 50, 50);
    Color blue = new Color(50, 50, 120);

    BufferedImage blueDiscBuf = new BufferedImage(bounds.x + bounds.width, bounds.y + bounds.height, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g2 = blueDiscBuf.createGraphics();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setPaint(blue);
    g2.fill(blueDisc);
    g2.dispose();

    int nComposites = alphaComposites.length;
    for(int i=0; i<nComposites; i++){
      // Set default composite and paint a red square
      g.setPaint(red);
      g.setComposite(AlphaComposite.SrcOver);
      g.fill(redDisc);

      // Set current composite and blue paint
      g.setPaint(blue);
      g.setComposite(alphaComposites[i]);
      g.fill(blueDisc);
      // g.drawImage(blueDiscBuf, 0, 0, null);

      if((i%2)==0)
	g.translate(bounds.width, 0);
      else
	g.translate(-bounds.width, bounds.height);
    }

  }

  /**
* Note the different behavior if you use the commented line
   * instead of the offscreen buffer. The reason is that the
   * offscreen buffer has an alpha channel.
   */
  public void paint(Graphics _g){
    // Use offscreen
    _g.drawImage(buf, 0, 0, null);

    // Alternate, direct rendering. Uncomment to see
   

 // difference.

    // paintGraphics((Graphics2D)_g);
  }

  public static void main(String args[]){
    JFrame frame = new JFrame();
		frame.getContentPane().add(new AlphaCompositeRules());
		frame.getContentPane().setBackground(Color.white);
		frame.pack();

  	
	frame.addWindowListener(new WindowAdapter(){
				public void windowClosing(WindowEvent evt){

					System.exit(0);
				}
			});

		frame.setVisible(true);
  }