Flashing

[Supamagier]

Hello, I did a little test and I have a problem.

Here's my code:

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

public class Test1
             extends JFrame
                     implements Runnable
{
    private Test1() {
        super("Test");
        setSize(1000,500);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(null);
        setBackground(Color.white);
        setResizable(false);
        setVisible(true);
        add((panel = new Test2(this)));
        panel.setBounds(0,0,1000,500);
        thread = new Thread(this);
        thread.start();
        panel.requestFocus();
    }

    public void run() {
        while (true) {
            if (panel != null)
                panel.repaint();
            try {
                thread.sleep(cycletime);
            }
            catch (InterruptedException ie) {
            }
        }
    }

    public static void main(String[] args) {
        new Test1();
    }

    final Thread thread;
    final Test2 panel;
    final int cycletime = 20;
}

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

public class Test2
             extends JPanel
{

    Test2(Test1 t) {
        setLayout(null);
        
        t3 = new Test3();
        t3.setBounds(0,0,800,500);
        add(t3);
        menuBar = new MenuBar();

        menu = new Menu[4];
        menuItems = new MenuItem[11];
        menu[0] = new Menu("A");
        menu[0].add(menuItems[0] = new MenuItem("1"));
        menu[0].add(menuItems[1] = new MenuItem("2"));
        menu[0].add(menuItems[2] = new MenuItem("3"));
        menu[1] = new Menu("B");
        menu[1].add(menuItems[3] = new MenuItem("4"));
        menu[2] = new Menu("C");
        menu[2].add(menuItems[4] = new MenuItem("5"));
        menu[2].add(menuItems[5] = new MenuItem("6"));
        menu[2].add(menuItems[6] = new MenuItem("7"));
        menu[2].add(menuItems[7] = new MenuItem("8"));
        menu[2].add(menuItems[8] = new MenuItem("9"));
        menu[2].add(menuItems[9] = new MenuItem("10"));
        menu[3] = new Menu("D");
        menu[3].add(menuItems[10] = new MenuItem("11"));
        t.setMenuBar(menuBar);
        for (Menu m : menu)
            menuBar.add(m);
    }

    public void paint(final Graphics g) {
        if (b == null) {
            off = new BufferedImage(200,500,BufferedImage.TYPE_INT_ARGB);
            b = off.getGraphics();
        }
        t3.repaint();
        b.setColor(Color.red);
        b.fillRect(0,0,200,500);

        g.drawImage(off,800,0,this);
    }
    
    public void update(final Graphics g) {
        paint(g);
    }
    
    BufferedImage off;
    Graphics b;
    private final       MenuBar         menuBar;
    private final       Menu[]          menu;
    private final       MenuItem[]      menuItems;
    Test3 t3;
}

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

public class Test3
             extends JPanel
{

    public void paint(final Graphics g) {
        if (b == null) {
            off = new BufferedImage(800,500,BufferedImage.TYPE_INT_ARGB);
            b = off.getGraphics();
        }
        b.setColor(Color.green);
        b.fillRect(0,0,800,500);
        g.drawImage(off,0,0,this);
    }

    public void update(final Graphics g) {
        paint(g);
    }

    BufferedImage off;
    Graphics b;

}

My problem: The green area (drawn by class Test3) keeps flashing white as I move my mouse over the menus (fast). Does anybody know what I'm doing wrong?

Help please. :)

[OrangeDog]

You're calling paint directly instead of calling repaint()

[Supamagier]

panel.repaint();
t3.repaint();

Only in the update methods - as it should (I heard). It doesn't help anyway, I tried. :(

[OrangeDog]

You don't appear to need those update methods at all. You also don't need to call t3.repaint() from within Test2.paint(). I also don't see a validate() anywhere.

[Supamagier]

Hmm, I checked, and indeed, the update methods are never called - while they, I'm sure, are needed for proper double buffering. Must be doing something wrong.

What do you mean by validate?

[Supamagier]

Nvm,

I solved it ;)

I had to call panel.repaint() directly from the mainclass's paint method.

Thx for your help anyway ;)

[OrangeDog]

update() isn't going to get called unless you call it yourself.

You need a boolean flag to check whether the BufferedImage is up-to-date. Then the paint() method checks this and either paints the image on the Graphics, or paints the new stuff on both.

I was referring to Container.validate(), which is required after adding/removing components.