Re-painting

Hello everyone,
I have an image that displayed on a JFrame.
I added a key listener and when i press right or left the image moves but I don't know how to "clean" the last place the image been.
Here is a picture to demonstrate:
Attachment 4211
So how do I clean my tracks?

Thanks in advacned.

Sounds like you're missing a call to super.paintComponent(), but without seeing an SSCCE, I'm only guessing.

I like it the way it is: a bunch of tiny Eskimos, neatly lined up and looking scared to death (maybe they just saw a ferocious yeti ;-)

kind regards,

Jos

Quote:

---

Originally Posted by JosAH

I like it the way it is: a bunch of tiny Eskimos, neatly lined up and looking scared to death (maybe they just saw a ferocious yeti ;-)

kind regards,

Jos

---

I think it looks like an Eskimo Caterpillar!

Thank you!
It's working now but I got another problem now.
When I click the picture disapear and then re-apear in the new position, this proccess takes to long so my picture kinda disapear for alot of time (less the a second of course)
so when I give a long press on the button the picture disapear.

Code:

---

public void paint(Graphics g)
        {
                super.paintComponents(g);
                g.drawImage(this.img1, this.posX, this.posY, null);
        }

---

You need to understand Swing's threading model.
Lesson: Concurrency in Swing (The Java™ Tutorials > Creating a GUI With JFC/Swing)
How to Use Swing Timers (The Java™ Tutorials > Creating a GUI With JFC/Swing > Using Other Swing Features)

db

I read this 2 links.
I know how to work with threads, and looks like the answer is in the first link.
But I don't understand how to use the Timer class.. it needs an actionListener as a parameter but my image moves by the keys which is a key listener.
And I'm confused how to use the timer.. I'm confused.

edit:
I tryed to make a thread let it sleep for a while then re paint but I still get the same results.

Something like that:

Code:

---

public void keyPressed(KeyEvent arg0) {
                switch(arg0.getKeyCode())
                {
                        case KeyEvent.VK_LEFT:
                        {
                                this.posX -= 1;
                                Update u1 = new Update(this);
                               
                        }
                }

---

Code:

---

public class Update extends Thread
{
        private Game g1;
        public Update(Game g1)
        {
                this.g1 = g1;
                this.run();
        }
        public void run()
        {
               
                try {
                        sleep(10);
                } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }
                this.g1.repaint();
        }
}

---

I tryed diffrent values for the sleep method.

Quote:

---

Originally Posted by tnrh1

Attachment 4211

---

Oh my God!
They duplicated Kenny!

(sorry, couldn't resist)

Super.paintComponent() clears the component, then draws the new picture on it. That's what we see as flicker. JComponent.paintComponent() calls JComponentUI.update() which clears the component:

Code:

---

public void update(Graphics g, JComponent c) {
  if (c.isOpaque()) {
    g.setColor(c.getBackground());
    g.fillRect(0, 0, c.getWidth(),c.getHeight());
  }
  paint(g, c);
]

---

You should override de update(Graphics) method and implement a double buffer technique, It's not as hard as it sounds. What you basically do is create an image the size of you component, draw on it, and when it's done, copy it to the Graphics of the component.
Here's (Java Cooperation: double buffering) a link I found googling for "java double buffer paint". Experiment with that.

Quote:

---

Originally Posted by SurfMan

Super.paintComponent() clears the component, then draws the new picture on it. That's what we see as flicker. JComponent.paintComponent() calls JComponentUI.update() which clears the component:

Code:

---

public void update(Graphics g, JComponent c) {
  if (c.isOpaque()) {
    g.setColor(c.getBackground());
    g.fillRect(0, 0, c.getWidth(),c.getHeight());
  }
  paint(g, c);
]

---

You should override de update(Graphics) method and implement a double buffer technique, It's not as hard as it sounds. What you basically do is create an image the size of you component, draw on it, and when it's done, copy it to the Graphics of the component.
Here's (Java Cooperation: double buffering) a link I found googling for "java double buffer paint". Experiment with that.

---

Sorry, but I disagree with this advice. Darryl had it right when he recommended understanding Swing's threading better. It seems like the OP is tying up the EDT, which is A Very Bad Thing. But like I said, without an SSCCE, we're just guessing.

Quote:

---

Originally Posted by KevinWorkman

Sorry, but I disagree with this advice. Darryl had it right when he recommended understanding Swing's threading better. It seems like the OP is tying up the EDT, which is A Very Bad Thing. But like I said, without an SSCCE, we're just guessing.

---

I think we're both right. The EDT is tied up, and the image is not cleared when Kenny is moved. :) An SSCCE would indeed be appreciated.

It's not such a long code so I past it all:

Game class

Code:

---

package pack1;

import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.sql.Time;

import javax.swing.*;

public class Game extends JFrame implements KeyListener
{
        private Image img1;
        private int posX;
        private int posY;
        public Game()
        {
               
                setSize(900, 900);
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setLocationRelativeTo(null);
                setVisible(true);
                addKeyListener(this);
               
                this.posX = (getWidth()/2)-(29/2);
                this.posY = getHeight()-70;
                this.img1 = getToolkit().getImage("kenny.gif");

        }
        public void paint(Graphics g)
        {
                super.paintComponents(g);
                g.drawImage(this.img1, this.posX, this.posY, null);
        }

        public void incX(int x){
                this.posX += x;
        }
       
        @Override
        public void keyPressed(KeyEvent arg0) {
                switch(arg0.getKeyCode())
                {
                        case KeyEvent.VK_LEFT:
                        {
                                this.posX -= 1;
                                new Update(this);       
                        }break;
                       
                        case KeyEvent.VK_RIGHT:
                        {
                                this.posX += 1;
                                new Update(this);
                        }
                }
               
        }
        @Override
        public void keyReleased(KeyEvent arg0) {
                //System.out.println(arg0);
               
        }
        @Override
        public void keyTyped(KeyEvent arg0) {
                //System.out.println(arg0);
               
        }

       
        public static void main(String[] args)
        {
                new Game();
        }

}

---

Update class

Code:

---

package pack1;

public class Update extends Thread
{
        private Game g1;
        public Update(Game g1)
        {
                this.g1 = g1;
                this.run();
        }
        public void run()
        {
               
                try {
                        sleep(10);
                } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }
                this.g1.repaint();
        }
}

---

Again, the problem is when I click left or right the image DISAPEAR for x time and then re-appear in the new position and this proccess takes to much time so it looks bad you can test it.
I can't show you a screen shot because of this situation xD

Thanks in advanced!

Yeah, you're tying up the EDT. You aren't doing threading correctly at all, so you're doing everything on the EDT. That's causing your program to become unresponsive.

First of all, follow this tutorial: Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing) - you should be extending JPanel, not JFrame.

Then get rid of your Thread class completely. For your purposes, you should be able to simply call repaint() from the KeyListener. Eventually you'll probably want to use a Swing Timer.

Do not use run() on a Thread. Instead, use start() to actually spawn the new Thread (Update.class, line 9).

Other than that, with the current code, the image is visible all the time here when I move it left and right, so I don't have your problem. What version JDK are you using?

Quote:

---

Originally Posted by SurfMan

Do not use run() on a Thread. Instead, use start() to actually spawn the new Thread (Update.class, line 9).

Other than that, with the current code, the image is visible all the time here when I move it left and right, so I don't have your problem. What version JDK are you using?

---

The threading issues are going to make this program's behavior unpredictable on different platforms. Threads are completely unnecessary here, so I'd highly recommend simply taking the threading out entirely.

Quote:

---

Originally Posted by KevinWorkman

The threading issues are going to make this program's behavior unpredictable on different platforms. Threads are completely unnecessary here, so I'd highly recommend simply taking the threading out entirely.

---

True. A simple repaint() will do for now. I agree with all your comments above. I wasn't trying to change his mind, or yours for that matter, just pointed him to a basic Thread error.

Ok I followed that guide and I'm using the JPanel now but it's leading me to another error, my keyListener doesn't respond to any key pressed.

Game:

Code:

---

package pack1;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Game
{
        public static void main(String[] args)
        {
                SwingUtilities.invokeLater(new Runnable()
                {
                    public void run()
                    {
                        createAndShowGUI();
                    }
                });
            }

            private static void createAndShowGUI()
            {
                JFrame f = new JFrame("My game");
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.add(new MyPanel());     
                f.pack();
                f.setLocationRelativeTo(null);
                f.setVisible(true);
            }
}

---

MyPanel:

Code:

---

package pack1;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JPanel;

public class MyPanel extends JPanel implements KeyListener
{

        private Image img1;
        private int posX;
        private int posY;
       
    public MyPanel()
    {
            this.addKeyListener(this);
        this.posX = (getPreferredSize().width/2)-(29/2);
                this.posY = getPreferredSize().height-70;
                this.img1 = getToolkit().getImage("kenny.gif");
    }

    public void paint(Graphics g)
    {
            super.paintComponents(g);
            g.drawImage(this.img1, this.posX, this.posY, null);
    }
   
   
    public Dimension getPreferredSize()
    {
        return new Dimension(900,900);
    }

        @Override
        public void keyPressed(KeyEvent arg0)
        {
                if(arg0.getKeyCode() == KeyEvent.VK_LEFT)
                        this.posX --;
                else
                        this.posX++;
                repaint();
        }

        @Override
        public void keyReleased(KeyEvent arg0) {
                // TODO Auto-generated method stub
               
        }

        @Override
        public void keyTyped(KeyEvent arg0) {
                // TODO Auto-generated method stub
               
        }
}

---

Ah, yeah. You have to make sure your JPanel is focusable, then you need to request that it has the focus in the window. Both methods are in the API: JPanel (Java Platform SE 7 )

Ok I added this line: this.setFocusable(true);
It's working now but I'm turning to my first error now:
Attachment 4212

It doesn't seem to make sense to call super.paintComponents() inside a paint() method. Shouldn't that be just super.paint() instead of super.paintComponents()?