Drawing image so that it appears on top of another

Question

Alright, this question isn't as straight forward as it may seem. Yes, I want to draw an image so that it appears on top of another drawn image, but the image I am trying to draw is being drawn in another thread like so:
public class myApplet extends Applet implements Runnable
  public Graphics g;
  public Thread myThread;
  public void init()
    myThread = new Thread(this);
    myThread.start();
  public void paint()
     super.paint(g);
     //Assume that I loaded in the images properly
     g.drawImage(image1, 0, 0, null); //Assume image1 is a 50 px X 50 px image
  public void run()
     g.drawImage(image2, 0, 0, null); //Assume image2 is a 20 px X 20 px image
}This also happens if I try to do "g.fillRect();". The 50 X 50 image appears on top of the 20 x 20 image. Does anyone know a way that I can tell the program to draw the image in the thread AFTER the image in the paint method (I know I should be using paintComponent, but this is a sample program. Please don't get too picky about it. I typed it up simply for this post and I wanted to make it simple).
The reason I'm drawing it in the paint method is because I am making an image move along a set of points. The points are formulated inside the run() method. If I draw it inside of the paint() method it skips points.
Any help would be GREAT. Thank you.
Edited by: dustty1818 on Apr 11, 2009 9:05 AM

Answer 1

dustty1818 wrote:
public class myApplet extends Applet implements Runnable
public Graphics g;
public void run()
g.drawImage(image2, 0, 0, null); //Assume image2 is a 20 px X 20 px image
}Edited by: dustty1818 on Apr 11, 2009 9:05 AMDusty,
There are several serious (fatal) flaws with your design. The biggest is that you should NEVER hold
on to a Graphics object. If anything you should be calling dispose at the end of the paint method.
It appears that you are accidentally trying to use a technique called "active rendering".
You can do active rendering in Java but it would look nothing like what you are doing (and is much
more advanced). You must resolve to keep all drawing in (or preferably called from) the paint method.
Have your run() method call repaint() and have your paint() method have all the information it
needs to render the scene.
Also, and this is comparatively minor, extend JApplet.
example:
import java.awt.*;
import javax.swing.*;
public class SceneRenderer extends JApplet implements Runnable{
     Point pt1 = new Point(0, 0);
     Point pt2 = new Point(0, 0);
     public void init(){
          Thread animationThread = new Thread(this);
          animationThread.start();
     public void paint(Graphics g){
          super.paint(g);
          g.setColor(Color.RED);
          g.fillRect(pt1.x, pt1.y, 50, 50);
          g.setColor(Color.BLUE);
          g.fillRect(pt2.x, pt2.y, 20, 20);
     public void run(){
          while(true){
               pt1.x += 1;
               pt2.x += 1;
               repaint();
               try{
                    Thread.sleep(60);
               } catch(Exception e){}
}