Help Me: I don't know whats wrong with my code

Java 2D
#1

This is the first time I am using threads. In my code below, i’ve tried to use threads with double buffering, and although the code compiles, I see nothing on the screen, can you please help me.

Thanx


import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

class Game extends JPanel implements ActionListener, Runnable
{
      int X = 40,Y = 40;
      private ImageIcon images[];
      private static final int TOTAL_IMAGES=7;
      private int currentImage = 0;
      boolean running = true;
      public static Image offscreen;
      
      public Game() 
      {
              setVisible(true);
              setupAnimation();
              setIgnoreRepaint(true);      
      }
      
   
      public void setupAnimation()
      {
            this.setSize(this.getPreferredSize());
            this.images = new ImageIcon[TOTAL_IMAGES];
            
            for (int i = 0; i < images.length; i++)
            {
                  images[i] = new ImageIcon("pac"+i+".gif");
            }
      }
      
      public void run()
      {
            offscreen= createImage(400,400);
              Graphics buff = offscreen.getGraphics();
              buff.setColor(Color.black);
              buff.fillRect(0,0,400,400);
 
            try
            {
                  while (running)
                  {
                        buff.drawImage(images[currentImage].getImage(), X, Y, this);
                        images[currentImage].paintIcon(this, buff, X, Y);
                        currentImage = (++currentImage) % TOTAL_IMAGES;
                        paint(buff);
                        Thread.sleep(30);
                  }
            }
            catch (Exception e) {}
      }
      
      public void paint(Graphics g) 
      {
            if (offscreen != null)
            {
                  g.drawImage(offscreen, 0, 0, this);
            }
      }
      
      public void actionPerformed(ActionEvent e){ repaint(); }
      public Dimension getMinimumSize() { return getPreferredSize(); }
      public Dimension getPreferredSize (){return new Dimension(400,400);}
      
       public static void main(String agrs[])
   {
        Game ji = new Game();
        JFrame main = new JFrame("PacMan");
        main.getContentPane().add(ji, BorderLayout.CENTER);
        main.pack();
        main.show();
        Thread t = new Thread(ji);
        t.start();
  } 
}
#2

You aren’t trying to draw to the JPanel, you are drawing the image to the buffer and not doing anything to the displayed JPanel. To fix, try doing this:


public void run()
 {
  offscreen= createImage(400,400);
    Graphics buff = offscreen.getGraphics();
    buff.setColor(Color.black);
    buff.fillRect(0,0,400,400);

  try
  {
   while (running)
   {
    buff.drawImage(images[currentImage].getImage(), X, Y, this);
    images[currentImage].paintIcon(this, buff, X, Y);
    buff.drawString("TEST", 30, 30);
    currentImage = (++currentImage) % TOTAL_IMAGES;
    paint(this.getGraphics());
    Thread.sleep(30);
   }
  }
  catch (Exception e) {}
 }

This works because it gets the Graphics object for the JPanel, and therefore renders it to something the user can see, rather than the buffer. I think that should work, sorry if it does’t :slight_smile:

Stuart

#3

Yes it works, Thanks alot

p.s. I just realised that if I use repaint(); it will also work. But I think I’ll stick with what you said.

Thanks again :slight_smile:

#4

repaint() shouldn’t work because you are ignoring repaint calls (setIgnoreRepaint(true))! Correct me if I am wrong :slight_smile:

Stuart

#5

It actually does work. To be honest, I am also surprised about this. ??? Could it be because I have put setIgnoreRepaint(true); in the wrong place? If anyone does know why this happens, then please tell me.

#6

You set it in A correct place (you can call it anytime)! I am just surprised that it hasn’t disabled repaint(), maybe it allows the user to call repaint() manually

Stuart

#7

isn’t javadoc a wonderful thing ;D