Re: Graphics help please

Knute Johnson <>
Sun, 27 Jan 2008 10:38:24 -0800
Rexx Magnus wrote:

On Sat, 26 Jan 2008 20:31:18 -0000, Knute Johnson
<> wrote:

Actually, I don't think the code below helps me much with what I want to
do (draw images pixel by pixel) as I don't want to clear the entire
image before displaying the changes, which is effectively what happens
below. I just used the circle as test code to render with pixels. How do
I just add to the image and then display that without clearing it each

The JPanel is buffered so that it doesn't actually clear the screen just
the offscreen buffer. You can't draw a circle pixel by pixel with the
technique you used. It will produce gaps because it only draws a pixel
and every degree of angle and not the points in between.

It would be easy to modify the code I provided to draw on an image
instead of the JPanel. You still must do any delaying outside of the
paintComponent() method or you will block the Event Dispatch Thread and
none of the rest of your GUI will respond and it probably won't show
anything until it is finished.

So since you haven't told us exactly what you are going to display in
this slow drawing it is still my opinion that it is better to draw it in
paintComponent() unless there is some compelling reason not to.

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

public class test2 extends JPanel implements Runnable {
     private final BufferedImage bi;
     private volatile int angle;

     public test2() {
         bi = new BufferedImage(300,300,BufferedImage.TYPE_INT_ARGB);
         setPreferredSize(new Dimension(300,300));

     public void run() {
         while (--angle >= -360) {
             try {
             } catch (InterruptedException ie) {

     void render() {
         Graphics2D g = bi.createGraphics();

     public void paintComponent(Graphics g) {

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame();
                 test2 t2 = new test2();
                 new Thread(t2).start();


Knute Johnson
email s/nospam/knute/

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