/**  
 *  How to use MediaTracker to load media first
 */

import java.awt.*;
import java.applet.*;

public class UseMediaTracker extends Applet {
 
 // initialize variables
 int appletWidth, appletHeight;
 // text ascent and descent
 int ascent, descent;
 // text width
 int stringWidth, x, y;
 Image bg, ship1, ship2, plane1, plane2;
 MediaTracker tracker;
 
 /**
  * (1)  overrides Applet init()  
  */
 public void init() {
  appletWidth = this.getSize().width;    //get Applet screen width
  appletHeight = this.getSize().height;  //get Applet Screen height
  
  // initialize image objects
  bg = getImage(getCodeBase(), "images/bg.gif");
  ship1 = getImage (getCodeBase(), "images/ship1.gif");
  ship2 = getImage (getCodeBase(), "images/ship2.gif");
  plane1 = getImage (getCodeBase(), "images/plane1.gif");
  plane2 = getImage (getCodeBase(), "images/plane2.gif");
  
  //initilize tracker object
  tracker = new MediaTracker(this);
  
  
  //adding images to the tracker
  tracker.addImage(bg, 0);
  tracker.addImage(ship1, 0);
  tracker.addImage(ship2, 0);
  tracker.addImage(plane1, 0);
  tracker.addImage(plane2, 0);
  
  try {
   this.showStatus("Loading...");
   tracker.waitForAll();
  }
  catch(InterruptedException E){};
 }
 
 /**
  * (2) Paint images
  */
 public void paint (Graphics g) {
  
  // if there are some errors happened when loading images
  if((tracker.statusAll(false) & MediaTracker.ERRORED) != 0) {
   FontMetrics fm = g.getFontMetrics();
   ascent =fm.getAscent();
   descent = fm.getDescent();
   stringWidth = fm.stringWidth("Loading Errors...");
   
   // calculate text center location
   x = (appletWidth - stringWidth) / 2;
   y = (appletHeight - (ascent + descent)) / 2 + ascent;
   
   this.setBackground(Color.black); //Applet background color
   g.setColor(Color.white);         //text color
   g.drawString("Loading Errors...", x, y); //centered text
   
   return;   
  }
  
  //if loading is successful, then draw images
     g.drawImage(bg, 0, 0, 320, 240, this);
     g.drawImage(ship1, 20, 140, 80, 80, this);
     g.drawImage(ship2, 180, 140, 80, 80, this);
     g.drawImage(plane1, 30, 10, 100, 100, this);
     g.drawImage(plane2, 250, 50, 50, 50, this);
     
 }

}