Gray box where my applet should be

[lee gardiner]

I have developed the following program which allows the user to move a box around the screen. The surface of the box is painted with an image that changes upon every key press to give the impression of movement. This applet works fine in appletviewer but when i try to view it in a web browser such as IE it just comes up as a gray box. I know i have the html code right and the gif images are all in the same folder as the class file so this one has me puzzled. I would be very grateful if someone could look at my code and tell me where the problem is.
Many Thanks

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.awt.geom.*;
import java.applet.*;
 
/*
 // header - edit "Data/yourJavaAppletHeader" to customize
 // contents - edit "EventHandlers/Java Applet/onCreate" to customize
 */
 
public class KeyMove4a extends java.applet.Applet implements KeyListener 
{
    private Rectangle2D r;
    private Image images[];
    
    int numImages = 5;
    int counter = 0;
    int velocity, xPos, yPos, maxVelocity;
    
    boolean up, down, left, right;
    
    MediaTracker mt = new MediaTracker(this);
    
    BufferedImage bi;
    
    //buffering
    Image offScreen;
    Graphics2D g2d;
    
    public void init() 
    {       
        images = new Image[numImages];
        offScreen = createImage(getSize().width, getSize().height);
        
        for (int i = 0; i < numImages; i++) 
        {
            images[i] = getImage(getCodeBase(), "a" + i + ".Gif");
            mt.addImage(images[i], 0);
        }
        
        try 
        {
            mt.waitForID(0);
        } catch (InterruptedException e) {}
        
        xPos = 0;
        yPos = 0;
        
        up = false; 
        down = false;
        left = false; 
        right = false;
        
        velocity = 0;
        maxVelocity = 6;
        
        bi = new BufferedImage(images[counter].getWidth(this), images[counter].getHeight(this), BufferedImage.TYPE_INT_RGB);
        r = new Rectangle2D.Float(xPos, yPos, bi.getWidth(), bi.getHeight());                                           
               
        addKeyListener(this);
        requestFocus();
        
        g2d = bi.createGraphics();
        g2d.setPaint(Color.black);
        g2d.fillRect(0, 0, getSize().width, getSize().height);
    }
    
    public void paint(Graphics g) 
    {       
        g2d = (Graphics2D) offScreen.getGraphics();
        //paints background white
        g2d.setPaint(Color.white);
        
        //erases the old image of the robot
        g2d.fillRect(0, 0, getSize().width, getSize().height);
        
        //this loop updates the images counter.
        if (counter >= numImages - 1)
            counter = 0;
        else 
            counter++;
        
        //this line draws the robot image upon the rectangle
        ((Graphics2D) bi.getGraphics()).drawImage(images[counter], new AffineTransform(), this);
        
        //moves the rectangle to the updated position
        r.setRect(xPos, yPos, images[counter].getWidth(this), images[counter].getHeight(this));
        
        //makes rectangle visible?
        g2d.setPaint(new TexturePaint(bi, r));
        
        //makes rectangle visible??
        g2d.fill(r);
        
        //Is this needed?
        g2d.dispose();
        
        //draws the buffered image to the screen.
        g.drawImage(offScreen, 0, 0, this);
    }
    
    public void start() 
    {
        System.out.println(">>START<<");
        repaint();
    }
    
    public void update(Graphics g) 
    {
        if (offScreen == null || offScreen.getWidth(null) != getSize().width ||
            offScreen.getHeight(null) != getSize().height) 
        {
            offScreen = createImage(getSize().width, getSize().height);
        }
        
        paint(g);   
    }
    
    public void keyPressed(KeyEvent e) 
    {
        switch (e.getKeyCode()) 
        {
            case KeyEvent.VK_LEFT:
                if (velocity <= maxVelocity)
                    velocity += 1;
                xPos = checkX(xPos) - 1 * velocity;
                repaint();
                left = true;
                break;
                
            case KeyEvent.VK_RIGHT:
                if (velocity <= maxVelocity)
                    velocity += 1;
                        
                xPos = checkX(xPos) + 1 * velocity;
                repaint();
                right = true;
                break;
                    
            case KeyEvent.VK_DOWN:
                if (velocity <= maxVelocity)
                    velocity += 1;
                yPos = checkY(yPos) + 1 * velocity;
                repaint();
                down = true;
                break;
                
            case KeyEvent.VK_UP:
                if (velocity <= maxVelocity)
                    velocity += 1;
                yPos = checkY(yPos) - 1 * velocity;
                repaint();
                up = true;
                break;
        }
        
        //moving in diagonals   
        if (up == true && left == true) 
        {
            if (velocity <= maxVelocity)
                velocity += 1;
            
            xPos = checkX(xPos) - 1 * velocity;
            yPos = checkY(yPos) - 1 * velocity;
        }
        
        if (up == true && right == true) 
        {
            if (velocity <= maxVelocity)
                velocity += 1;
            
            xPos = checkX(xPos) + 1 * velocity;
            yPos = checkY(yPos) - 1 * velocity;
        }
        
        if (down == true && left == true) 
        {
            if (velocity <= maxVelocity)
                velocity += 1;
        
            xPos = checkX(xPos) - 1 * velocity;
            yPos = checkY(yPos) + 1 * velocity;
        }
        
        if (down == true && right == true) 
        {
            if (velocity <= maxVelocity)
                velocity += 1;
        
            xPos = checkX(xPos) + 1 * velocity;
            yPos = checkY(yPos) + 1 * velocity;
        }
    }       
        
    public void keyTyped(KeyEvent e) {}
    
    public void keyReleased(KeyEvent e) 
    {
        velocity = 0;
        
        switch (e.getKeyCode()) 
        {
            case KeyEvent.VK_LEFT:
                left = false;
                break;
                    
            case KeyEvent.VK_UP:
                up = false;
                break;
            
            case KeyEvent.VK_DOWN:
                down = false;
                break;
            
            case KeyEvent.VK_RIGHT:
                right = false;
                break;
        }    
    }
    
    //methods to check if block has exited the screen
    public int checkX(int x) 
    {
        if (x > getSize().width)
            return x = 0;
        else if (x < 0)
            return x = getSize().width;
        
        return x;
    }
    public int checkY(int y) 
    {
        if (y > getSize().height)
            return y = 0;
        else if (y < 0)
            return y = getSize().height;
        
        return y;
    }
}

[ May 30, 2002: Message edited by: Dirk Schreckmann ]

[Keith Owen]

It is most likely a problem with your HTML. Swing can be tricky when it comes to that. Would you care to post your HTML document, or at least the part that references your applet?
-Keith

[Dirk Schreckmann]

Perhaps your browser doesn't have support for Java beyond version 1.1.8 installed. You may need to install the Java plug-in. Get it here:
http://java.sun.com/getjava/
Any luck yet?

[Pradyumna Hari]

Hi lee,
Please do post your html and the names of images used. I would be interested to analyse your program.

[Manish Hatwalne]

I also guess it's a problem with the JVM of your browser. What does Java Console show you? That should give you some idea abt the error.
- Manish

[lee gardiner]

Thanks for all your reply's as requested my html code is posted below. The names of my gif images are simply a1 to a6.

 
<html>
<head>
<meta name="generator" content="ModelWorks IDE">
<title>KeyMove</title>
</head>
<body>
<h1>Test page for KeyMove4a Class</h1><hr>
<applet code="KeyMove4a.class" width=400 height=500></applet>
<hr></body>
</html>
 

I have tried this in the latest version of netscape and explorer both show nothing but the gray box. I was thinking maybe some variables are not intialised but if this was the case why is it working in appletviewer. I have tried it on more than one pc, all giving the same results. I have also tried reducing the security settings on my browser to minimum to see if that has any affect, but it does not appear to have.
Again i am grateful for any advice you can give me.
Lee
[ May 31, 2002: Message edited by: Dirk Schreckmann ]

[lee gardiner]

Manish - Could you expand further upon what you where saying about the JVM and the Java Console. I have the latest version of Java, i think, and all my other applets display fine in web pages.
I feel a bit silly for asking this question but this is the beginner forum - what is the Java console and how do i access it. I just use dos to compile and edit my programs, is this what you mean by java console. The text books do a good job at teaching you the OOP principles but are not as good on the actual techology you use to run and compile your programs.
Thanks for any help.
Lee

[Dirk Schreckmann]

Originally posted by Dirk Schreckmann:
Perhaps your browser doesn't have support for Java beyond version 1.1.8 installed. You may need to install the Java plug-in. Get it here:
http://java.sun.com/getjava/
Any luck yet?

[Dirk Schreckmann]

If you'd like to determine what version of Java your browsers are using, you could use this code to find out:

public class Whatever extends java.applet.Applet 
{
    public void paint( java.awt.Graphics g ) 
    {
        g.drawString( System.getProperty( "java.version" ) , 100 , 100 );
    }
}

[Manish Hatwalne]

Originally posted by lee gardiner:
I feel a bit silly for asking this question but this is the beginner forum - what is the Java console and how do i access it. I just use dos to compile and edit my programs, is this what you mean by java console. The text books do a good job at teaching you the OOP principles but are not as good on the actual techology you use to run and compile your programs.
Lee

Hi Lee,
It's perfectly alright!
If you are using IE, you can see java console from "View" menu option -> Java Console. All your System.out.println() (if any) of applet are displayed here. Also, the exceptions are displayed here; which will give you an idea abt what's wrong with your code.
If you do not see "Java Console" option in your "View" menu of IE, you'll have to do - Tools |Internet Options |Advanced tab, under Microsoft VM, check "Java Console Enabled" and restart your browser. You should be able to see option "Java Console", in ur "View" menu now. You should also use the code that Dirk gave to determine the JVM of your browser. Though you may have the latest Java on ur machine, the JVM IE uses might be different. Let us know if it helps..
HTH,
- Manish