Tutorials : Java by Example : Section 3 :
Section Three Contents
Fonts, Random Numbers and Timers
Flicker Free Graphics, GIF and JPEG Display
Animation with GIF Pictures, Sprite Animation

Fonts and Graphics

Animation with GIF Pictures, Sprite Animation - Con't

To show animated sprites, you have to display several different pictures in rapid succession, to produce the animation effect. With the helper functions in this applet, you can easily load the frames of the sprite animation from a single image strip, that combines all pictures of the animation in one single picture. Look at the image file "running_dog.gif" to see what I mean. All the single pictures in the strip have to be the same size and position one below the other. To change the frames we use a ticker variable which is incremented. When a certain value is reached, the frame changes. The pictures for the animation are from the the free image collection SpriteLib by Ari Feldman. The background is a tiled 80x80 pixels image.

//Sourcecode 

import java.awt.*;
import java.applet.*;
//we have to import the image package!
import java.awt.image.*;

//a flicker free animation with animation phases!

public class Project12 extends Applet implements Runnable
{
   Thread runner;
   private Image Buffer;
   private Graphics gBuffer;
   int x, ticker=0, frame=0;

   Image background, dogStrip, dog[];

   //Init is called first, do any initialisation here
   public void init()
   {
      //create graphics buffer, the size of the applet
      Buffer=createImage(size().width,size().height);
      gBuffer=Buffer.getGraphics();

      background=loadImage("background.jpg");
      dogStrip=loadImage("running_dog.gif");

      dog = new Image[6];
      extractImages(dogStrip,dog,6,100,60);
   }

   public void extractImages(Image imagestrip, Image images[],int num,int width, int height)
   {
      ImageProducer source = imagestrip.getSource();

      for(int i=0; i<num; i++)
      {
          ImageFilter extractFilter=new CropImageFilter(0,i*height,width,height);
          ImageProducer producer = new FilteredImageSource(source,extractFilter);
          images[i] = createImage(producer);
      }
   }

   public Image loadImage(String imagename)
   {
      Image image=getImage(getDocumentBase(),imagename);
      MediaTracker tracker=new MediaTracker(this);
      tracker.addImage(image,0);
      try
      {
          tracker.waitForID(0);
      }
      catch(InterruptedException e){}

      return image;
   }

   public void start()
   {
      if (runner == null)
      {
         runner = new Thread (this);
         runner.start();
      }
   }

   public void stop()
   {
      if (runner != null)
      {
         runner.stop();
         runner = null;
      }
   }

   public void run()
   {
      Thread.currentThread().setPriority(Thread.MAX_PRIORITY);

      while(true)
      {
           //Thread sleeps for 15 milliseconds here
           try {runner.sleep(15);}
           catch (Exception e) { }

           //here we draw the tiled background
           for(int i=0;i<size().width;i+=80)
                for(int j=0;j<size().width;j+=80)
                    gBuffer.drawImage(background,i,j,this);

           x+=3;
           if(x>300)
               x=-100;

           ticker++;

           //this sets the animation phases
           //you can determine the speed of the phases change here
           if(ticker>3)
           {
               if(frame<5)
                   frame++;
               else
                   frame=0;

               ticker=0;
           }

           //draws the star animation
           gBuffer.drawImage(dog[frame],x,45,this);

           repaint();
      }
   }

   //is needed to avoid erasing the background by Java
   public void update(Graphics g)
   {
        paint(g);
   }

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

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