// GraphicAnimationOverABackground
// modeled on code found at
//	http://www.dgp.toronto.edu/~mjmcguff/learn/java/07-backbuffer/

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class AnimationOfAnImageOverABackgroundWithBackbuffer extends JApplet implements MouseMotionListener 
{
   private int width;
   private int height;
   private int mx;
   private int my; 
   private Image backgroundImage;
   private Image spaceshipImage;
   private Image backbuffer;
   private Graphics backg;

   public void init() 
   {
      width = getSize().width;
      height = getSize().height;
      mx = width/2;
      my = height/2;

      backgroundImage = getImage(getDocumentBase(), "background.gif");
	  spaceshipImage = getImage(getDocumentBase(), "spaceship.gif");
	  
      backbuffer = createImage(width, height);	// backbuffer is an off-screen drawable image to be used for double-buffering
      backg = backbuffer.getGraphics();			// backg is a reference to the Graphics object property of the Image backbuffer & can now serve as a context for drawing an off-screen image (i.e. like the paint method's parameter g)

      addMouseMotionListener(this);
   }

   public void mouseMoved(MouseEvent e) 
   {
      mx = e.getX();
      my = e.getY();

      backg.drawImage(backgroundImage, 0, 0, this);
      backg.drawImage(spaceshipImage, mx, my, this);

      repaint();
      e.consume();
   }
   
   public void mouseDragged(MouseEvent e) {}

   public void update(Graphics g)   // must override the Component class's update method to prevent applet from being cleared (i.e. filled with the background color)
   {								//	otherwise, flickering will occur
      g.drawImage(backbuffer, 0, 0, this);
   }

   public void paint(Graphics g) 
   {
      g.drawImage(backgroundImage, 0, 0, this);
      update(g);
   }
}