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  Applet game method invocation order  (Read 300 times)
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Offline mathdaemon

Innocent Bystander





« Posted 2013-03-03 05:56:05 »

Hi there
I am new here as well as game dev. After three years of programming i have finally zeroed in on what i want to do i.e. develop games.
Enough of the introduction, I need your help to figure out the order of execution of an applet program.I am developing my first GUI based game using Applet(I am following a tutorial). So here it is

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public class StartingPoint extends Applet implements Runnable {

   
   private Image i;
   private Graphics double_G;
   Ball b;
   
   public void run()
   {  
      while(true)
      {
                 
         repaint();
         
         try
         {
            Thread.sleep(17);
         }
         catch(InterruptedException ie)
         {
            ie.printStackTrace();
         }
      }
   }
   
   public void init()
   {
      setSize(800,600);
   }
   
   public void start()
   {
      b= new Ball();
      Thread t=new Thread(this);
      t.start();
   }
   
   public void update(Graphics g)
   {
      b.update(this);
      if(i==null)
      {
         i=createImage(this.getWidth(),this.getHeight());
         double_G=i.getGraphics();
      }
      double_G.setColor(getBackground());
      double_G.fillRect(0, 0, this.getWidth(), this.getHeight());
      paint(double_G);
      g.drawImage(i, 0, 0, this);
   }
   
   public void paint(Graphics g)
   {
      b.paint(g);
   }
   
   public void stop()
   {}
   
   public void destroy()
   {}

}

public class Ball
{
   private int x=0,y=0;
   private double dx=20,dy=0;
   private int radius=30;
   private double gravity=15,energyloss=0.65,dt=0.2,xFriction=0.9;
   
   public void update(StartingPoint sp)
   {
      if(x+dx>sp.getWidth()-radius-1)
      {
         x=sp.getWidth()-radius-1;
         dx=-dx;
      }
     
      else if(x+dx<0)
      {
         x=0;
         dx=-dx;
      }
     
      else
      {
         x+=dx;
      }
     
      if(y==sp.getHeight()-radius-1)
      {
         dx*=xFriction;
         if(Math.abs(dx)<0.8)
            dx=0;
      }
     
      //ball hits the ground
      if(y>sp.getHeight()-radius-1)
      {
         y=sp.getHeight()-radius-1;
         dy*=energyloss;
         dy=-dy;
      }
     
      else
      {
         //change in displacement
         dy+=gravity*dt;
         //new position of the ball
         y+=dy*dt+0.5*gravity*dt*dt;
      }

   }
   
   public void paint(Graphics g)
   {
      g.setColor(Color.BLUE);
      g.fillOval(x, y, radius, radius);
   }
}


i am a little confused about the order of execution of the above code.
Here is what i think it should be
init()
start()
run()-->repaint()(which actually calls paint() and paint() calls update())
Am I correct?
If I am correct and the update() gets called before the paint(), when the applet runs the first how does it obtain the graphics context/Canvas to print upon?
Also, initially I assign x and y, the value 0, because i want it start at 0,0 but since the update method is called before paint the x and y values get updated before the first paint().
I think the source code I have posted is really long.I am sorry for that.It would be really kind if someone would help me.
Thanks in advance

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