//****************************************************************************** 
// ----------------------------------------------------------- 
// 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) ; 
     } 

  }