Some two threaded image prepare and painting applet coordination problem

Question

hi all,
i'm sure this multithreaded gui is complex but anyway. a simple producer&consumer type applet. there is one seperate thread preparing an offscreen image, and the main guy draws it on applet. i can not coordinate them, what's wrong i don't know. simply, applet starts a thread, which paints something on an offscreen image, and then tells to applet repaint(). anyway, here is the code, this small png files are a lot, idea is making a view on them, just imagine a big big png file divided into matrices. afterall this is not the important part. what i see on the screen is, if you ask, nothing.
thanx,
ozz
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.lang.reflect.Array;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MapViewer
     extends JFrame
     Image map[][];
     public MapViewer()
          int dimensions[] = { 58, 46 };
          map = (Image[][]) Array.newInstance(Image.class, dimensions);
          try
               loadImages();
          catch(Exception e)
               e.printStackTrace();
     public void loadImages()
          throws Exception
          for(int i=0; i<58; i++)
               for(int j=0; j<46; j++)
                    StringBuffer sb = new StringBuffer();
                    sb.append("C:\\map\\");
                    sb.append(i+1);
                    sb.append("_");
                    sb.append(46-j);
                    sb.append(".png");
                    map[i][j] = Toolkit.getDefaultToolkit().getImage( sb.toString() );
     public void go()
          initComponents();
          show();
     private void initComponents()
          addWindowListener
               new java.awt.event.WindowAdapter()
                    public void windowClosing(java.awt.event.WindowEvent evt)
                         exitForm(evt);
          getContentPane().setLayout(new BorderLayout());
          getContentPane().add(new MapPanel(), BorderLayout.NORTH);
          pack();
     private void exitForm(java.awt.event.WindowEvent evt)
          System.exit(0);
     public static void main(String args[])
          new MapViewer().go();
     private class MapPanel
          extends JPanel
          implements MouseMotionListener, Runnable
          private int north = 1;
          private int east = 2;
          private int south = 4;
          private int west = 8;
          private int direction;
          private Image model;
          private Boolean refreshModel = Boolean.TRUE;
          private Boolean modelReady = Boolean.FALSE;
          private Point start = new Point(200, 200);
          public MapPanel()
               addMouseMotionListener(this);
               new Thread(this).start();
          public synchronized Image requestImage()
               return createImage(1600, 1600);
          public Dimension getMinimumSize()
               return new Dimension(400, 400);
          public Dimension getPreferredSize()
               return new Dimension(400, 400);
          public void paint(Graphics g)
               synchronized(modelReady)
                    if(modelReady.booleanValue() == true)
                         g.drawImage(model, 0, 0, null);
               g.setColor(Color.white);
               g.fillRect(0, 0, 30, 10);
               g.setColor(Color.black);
               g.drawString(String.valueOf(direction), 0, 10);
          public void mouseDragged(MouseEvent e)
          public void mouseMoved(MouseEvent e)
               Point p = e.getPoint();
               findDirection(p);
          private void findDirection(Point p)
               direction = 0;
               if(p.x < 100)
                    direction |= west;
               else if(p.x > 300)
                    direction |= east;
               if(p.y < 100)
                    direction |= north;
               else if(p.y > 300)
                    direction |= south;
          public void moveIt()
               int px = 20;
               int py = 20;
               synchronized(refreshModel)
                    if(refreshModel.booleanValue() == true)
                         model = requestImage();
                         if(model == null || model.getGraphics() == null)
                              return;
                         Graphics g = model.getGraphics();
                         for(int x=0; x < 4; x++)
                              for(int y=0; y<4; y++)
                                   g.drawImage(map[px+x][py+y], x*200, y*200, null);
                         refreshModel = Boolean.FALSE;
                         modelReady = Boolean.TRUE;
//               start.x -= 3;
//               start.y -= 3;
          public void run()
               while(true)
                    try
                         moveIt();
                         repaint();
                         Thread.currentThread().sleep(20);
                    catch(InterruptedException ie)

Answer 1

Hi.
The Graphics.drawImage method is asynchronyous, that may be the reason of the problem. Set an ImageObserver parameter in drawImage method, when drawing on an offscreen image. Count finished images and when all are done
draw the big image on the screen.
Alternatively you can call Toolkit.prepareImage method in a loop, after loadimages and wait until all images are loaded(true returned).