Help redrawing large image

Question

I have a 600x600 applet that redraws each pixel (drawing the mandelbrot set).
Right now (just using a for loop and paint() method) it swipes down drawing the pixels and takes a couple seconds.
I tried to draw an image offscreen and paint that on but it still took the same amount of time since it needed to still draw each pixel to the offscreen image.
I was wondering what I need to do to make it faster. Would threads be the solution?
Thanks

Answer 1

Kurbz wrote:
iterations = getIterations(real, imaginary);  //method that computes color for each pixel
if (iterations == maxIterations)
     g.setColor(Color.BLACK);
else {
     red = (iterations % 32) * 7;
     green = (iterations % 16) * 14;
     blue = (iterations % 128) * 2;
     g.setColor(new Color(red,green,blue));
g.drawLine(x,y,x,y);
My experiments show using the WritableRaster of a BufferedImage to be about 3 times faster than using setColor and drawLine (ignore hackish code):
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.swing.*;
public class GraphicsTest1 {
   static volatile boolean isPainted = false;
   private static final Dimension dim = new Dimension(800, 800);
   public static void main(String[] args) {
      final JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      final BufferedImage image = GraphicsEnvironment.getLocalGraphicsEnvironment()
         .getDefaultScreenDevice().getDefaultConfiguration().createCompatibleImage(
               dim.width, dim.height, BufferedImage.OPAQUE);
      final JPanel panel = new JPanel() {
         @Override
         protected void paintComponent(Graphics g) {
            if ( isPainted ) {
               g.drawImage(image, 0, 0, null);
            } else {
               super.paintComponent(g);
      final Thread t = new Thread(new Runnable() {
         @Override
         public void run() {
            WritableRaster raster = image.getRaster();
            Graphics2D gr = image.createGraphics();
            Random rnd = new Random();
            long nanos = System.nanoTime();
            for ( int x = 0; x < dim.width; x++ ) {
               for ( int y = 0; y < dim.height; y++ ) {
                  int r = rnd.nextInt(128)+128;
                  int g = rnd.nextInt(128)+128;
                  int b = rnd.nextInt(128)+128;
//                  setPixel(raster, x, y, r, g, b);
//                  setPixel(image, x, y, r, g, b);
                  setPixel(gr, x, y, r, g, b);
            System.out.printf("Seconds taken: %f%n", (System.nanoTime() - nanos) / 1000000000.0);
            gr.dispose();
            isPainted = true;
            panel.repaint();
      t.start();
      frame.setContentPane(panel);
      frame.setVisible(true);
      frame.setSize(dim.width, dim.height);
   private static void setPixel(WritableRaster raster, int x, int y, int r, int g, int b) {
      raster.setPixel(x, y, new int[] {r, g, b});
   private static void setPixel(BufferedImage image, int x, int y, int r, int g, int b) {
      image.setRGB(x, y, r << 16 | g << 8 | b );
   private static void setPixel(Graphics2D gr, int x, int y, int r, int g, int b) {
      gr.setColor(new Color(r, g, b));
      gr.drawLine(x, y, x, y);
}