Re: Graphics help please

Knute Johnson <>
Sun, 27 Jan 2008 17:13:02 -0800
Rexx Magnus wrote:

On Sun, 27 Jan 2008 18:38:24 -0000, Knute Johnson
<> wrote:

 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.

I'm trying to write a basic engine that I can use for all sorts of
purposes, one of them being for rendering fractals, but it needs to be
visible as it's being drawn so you can abort if it ends up being slow
besides other things - and also so that I can plot graphs and render
fields to show various effects such as gravity.

I'm not bothered about lines being discontinuous - I'm just trying to
replicate some old experimental programming, similar to what I used to
do in BASIC. It's just annoying that there has to be so much set-up just
to do something that is quite simple in a lot of other languages.

A lot of the stuff I write doesn't actually have a definite end, so it's
just a case of watching it draw and stopping it when you're satisfied.

OK. Well then I would definitely use an offscreen buffer and draw it to
the onscreen component on some sort of regular schedule. You can put a
repaint() call in your drawing thread or use another thread or a timer.

This example puts a 1ms delay between drawing elements and draws the
offscreen image to the onscreen every 200ms. Depending on how much
processing it takes to produce your pixels, you might not need the
drawing delay.

Sometimes it really is better to provide a little more information up
front about what you are actually trying to do so as to get a better
answer here.

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

public class test2 extends JPanel implements ActionListener, Runnable {
     private final BufferedImage bi;
     private final Random random;
     private final javax.swing.Timer timer;

     public test2() {
         bi = new BufferedImage(300,300,BufferedImage.TYPE_INT_ARGB);
         random = new Random(new Date().getTime());
         timer = new javax.swing.Timer(200,this);
         setPreferredSize(new Dimension(bi.getWidth(),bi.getHeight()));

     public void run() {
         while (true) {
             int x = random.nextInt(bi.getWidth());
             int y = random.nextInt(bi.getHeight());
             try {
             } catch (InterruptedException ie) {

     public void actionPerformed(ActionEvent ae) {

     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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