//******************************************************************************
// -----------------------------------------------------------
// tipsImg4.java ( Thread et Double Buffer )
// -----------------------------------------------------------
// Comments : very simple drawimage applet 
// with MediaTracker and double buffer
// -----------------------------------------------------------
// Author : R. BERTHOU
// E-Mail : rbl@berthou.com
// URL    : http://www.javaside.com
// -----------------------------------------------------------
// 1.00 * R.BERTHOU  * 16/04/2000 * samples tips
//******************************************************************************

 // Importations
 import java.awt.Graphics ;
 import java.awt.Image ;
 import java.awt.MediaTracker;
 import java.awt.Color;
 import java.awt.Image;
 import java.awt.Event;

 public class tipsImg4 extends java.applet.Applet 
					   implements Runnable
 {
     // Variables
     Image img ;                 // ...

	 Thread th ;

	 long delay = 5 ;

	 int xPos = 0 ;
	 int yPos = 0 ;

	 int aW = -1 ;
	 int aH = -1 ;
	 int iW = -1 ;
	 int iH = -1 ;

	 int cX = 1 ;
	 int cY = 1 ;

	 // true => double buffer active
	 boolean b = true ;

	 // for double buffering to prevent flicker
	 Image offScreenImage;
	 Graphics offScreen;

     // Initialisation de l'applet
     public void init() { 
	  MediaTracker  trk = new MediaTracker(this) ;

      // Lecture de l'image
      img =  getImage(getCodeBase(), "./photo.gif") ;

         // Ajout de l'image dans le MediaTracker
	  trk.addImage(img, 0) ;

      try {
			trk.waitForAll() ;
	  } catch (InterruptedException e) { }


     }

	// control the starting of the applet
	public void start() {
		// create thread
		th = new Thread(this);

		// start the thread
		th.start();

	} // end of start

	// control the stopping of the applet
	public void stop() {
			th.stop();
	} // end of stop

	// control the running of the applet
	public void run() {
		// set the priority of the thread to low
		Thread.currentThread().setPriority(Thread.MIN_PRIORITY);

		// loop continuously
		while(true) {
			// values for working out the constant delay
			long thisTick, waitTick;

			// calculate the tick to wait for
			waitTick = System.currentTimeMillis() + delay;

			// update the screen
			xPos += cX ;
			yPos += cY ;

			if (cX == 1) {
				if ( (xPos+iW) > aW) cX = -1 ;
			}
			else
				if ( xPos < 0) cX = 1 ;

			if (cY == 1) {
				if ( (yPos+iH) > aH) cY = -1 ;
			}
			else
				if ( yPos < 0) cY = 1 ;

			repaint ();

			thisTick = System.currentTimeMillis();

			if ( thisTick<waitTick ) {
				try {
					Thread.currentThread().sleep( (int)(waitTick-thisTick));
				} catch (InterruptedException e) {}
			}

		} 	// end of loop

	  } // end of run

	// if you click on the applet you active or remove double buffer
	public boolean mouseDown(Event e, int x, int y){
		b = !b ;
		return true ;
	}

	// Called when the applet needs to be painted
	// calls the flicker free updating system
	public void paint (Graphics g) {
		update(g);
	} // end of paint

	// Draw the applet without flicker
	public synchronized void update(Graphics g) {
		// get the size of the applet
		int xW = size().width ;
		int xH = size().height ;

		if ((xW != aW) || (xH != aH) || (offScreen == null)) {
			// initialise the double buffering screen
			try {
				offScreenImage = createImage (xW, xH);
				offScreen = offScreenImage.getGraphics ();
			} catch (Exception e) {
				offScreen = null;
			}
			aW = xW ;
			aH = xH ;

			// get Image size
			iW = img.getWidth(this) ;
			iH = img.getHeight(this) ;
		}

		if ((offScreen!=null) && b) {
			paintApplet(offScreen);
			g.drawImage(offScreenImage,0,0,this);
		}  else
			paintApplet(g);
	} // end of update

     // Draw applet
     public void paintApplet(Graphics g) { 
		  g.setColor(Color.white ) ;
          g.fillRect(0, 0, aW, aH) ;
          g.drawImage(img, xPos, yPos, this) ;
		  g.setColor(Color.red ) ;
		  g.drawString("double buffer : " + b, 10, yPos) ;
     }

  }