import java.awt.*;
import java.awt.event.*;
import java.awt.event.ActionListener;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.lang.reflect.Field;

import javax.swing.*;
import javax.swing.event.*;
import javax.swing.event.ChangeListener;

/**
 * @author Remi Forax
 *
 */
public class AlphaCompositionExample2 extends JComponent {

  protected void paintComponent(Graphics graphics) {
    super.paintComponent(graphics);

    Graphics2D g2= (Graphics2D)graphics;

    g2.setColor(Color.CYAN);
    g2.fillRect(0, 0, 200, getHeight());

    g2.setColor(Color.ORANGE);
    g2.fill(ellipse);

    if (composite!=null)
      g2.setComposite(composite);

    g2.drawImage(image,0,0,null);
    
    //g2.setColor(Color.RED);
    //g2.fill(rectangle);
  }

  private Composite composite;
  private final Image image=new ImageIcon(AlphaCompositionExample2.class.getResource("moon.jpg")).getImage();

  private static final Shape ellipse=new Ellipse2D.Float(50,50,100,100);
  private static final Shape rectangle=new Rectangle(100,100,150,100);

  static AlphaComposite getFieldValue(String name) {
    try {
      Field field=AlphaComposite.class.getField(name);
      return (AlphaComposite)field.get(null);
    } catch (NoSuchFieldException e) {
      throw new AssertionError(e);
    } catch (IllegalArgumentException e) {
      throw new AssertionError(e);
    } catch (IllegalAccessException e) {
      throw new AssertionError(e);
    }
  }

  void applyComposite(JCheckBox check,JSlider slider,JComboBox combo) {
    String rule=(String)combo.getSelectedItem();
    AlphaComposite composite=getFieldValue(rule);
    if (check.isSelected()) {
      float alpha=slider.getValue()/100.0f;
      composite=AlphaComposite.getInstance(composite.getRule(), alpha);
    }

    this.composite=composite;
    paintImmediately(0,0,getWidth(),getHeight());
  }

  public static void main(String[] args) {

    JFrame frame= new JFrame("CompositeExample");
    final AlphaCompositionExample2 component= new AlphaCompositionExample2();

     String[] rules=new String[]{
      "Clear", "Dst",     "DstAtop", "DstIn",
      "DstOut","DstOver", "Src",     "SrcAtop",
      "SrcIn", "SrcOut",  "SrcOver", "Xor"
     };

    final JSlider slider=new JSlider(0,100);

    final JCheckBox checkBox=new JCheckBox("alpha");
    checkBox.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        slider.setEnabled(checkBox.isSelected());
      }
    });

    final JComboBox comboBox=new JComboBox(rules);

    ActionListener listener=new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        component.applyComposite(checkBox, slider, comboBox);
      }
    };

    checkBox.addActionListener(listener);
    comboBox.addActionListener(listener);
    slider.addChangeListener(new ChangeListener() {
      public void stateChanged(ChangeEvent e) {
        component.applyComposite(checkBox, slider, comboBox);
      }
    });

    JPanel panel=new JPanel();
    panel.add(checkBox);
    panel.add(slider);
    panel.add(comboBox);

    frame.getContentPane().add(panel,BorderLayout.NORTH);
    frame.getContentPane().add(component);
    frame.setSize(400,300);
    frame.setVisible(true);
  }
}