Problem with huge graphic - Lines become noise

Question

Hi there,
I have a strange problem when drawing a huge graphic. Is is a kind of line-chart. The graphic (chart) is placed to a JPanel within a JScrollPane. The size can be configured and if it exceeds a size the lines are not visible anymore, but every pixel of the line is distributed within the whole graphic. It looks like noise or a snow flurry.
The line chart is updated (re-drawn) within a certain interval. I think no manual repaint is done and it happens and sometimes later is ok again and you can see the line chart and then its gone again.
Can can't exactly tell what the "critical" size is, but the chart is actually about 3000x300 pixels big.
The strange thing is, that never happens when unsing Java 1.4.XX, it is since Java 1.5, and does not happen with smaller size (at least I think so)
The lines are "PolyLines" with several thousand edges.
The code for creating this is like:
          m_bufImage = new BufferedImage(m_nWidth, m_nHeight, BufferedImage.TYPE_INT_RGB);
          m_imageG2D = m_bufImage.createGraphics();
          m_imageG2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
          m_imageG2D.setColor(m_colBg);
          m_imageG2D.fillRect(m_nWidth, m_nHeight, m_bufImage.getWidth(), m_bufImage.getHeight());               
          m_pnlChart.add(new JLabel(new ImageIcon(m_bufImage)));     
Any idea?
regards

Answer 1

Any idea?
Yes.
m_pnlChart.add(new JLabel(new ImageIcon(m_bufImage)));
Swing may have a hard time keeping up with repainting thousands of labels.
You could abandon the components and draw the polyLines directly into an image and draw that
for each repaint. Try this:
import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.swing.*;
public class SimpleDrawing extends JPanel {
    BufferedImage image;
    Random seed = new Random();
    protected void paintComponent(Graphics g) {
         super.paintComponent(g);
         if(image == null)
             initImage();
         g.drawImage(image, 0, 0, this);
    public Dimension getPreferredSize() {
        return new Dimension(3000, 300);
    private void draw() {
        Dimension d = getPreferredSize();
        int w = d.width;
        int h = d.height;
        int r = 20;
        int cx = r/2 + seed.nextInt(w - r);
        int cy = r/2 + seed.nextInt(h - r);
        int nPoints = 3 + seed.nextInt(4);
        int[] xPoints = new int[nPoints+1];
        int[] yPoints = new int[nPoints+1];
        double theta = 0;
        double thetaInc = 2*Math.PI/nPoints;
        for(int j = 0; j <= nPoints; j++) {
            xPoints[j] = (int)(cx + r*Math.cos(theta));
            yPoints[j] = (int)(cy + r*Math.sin(theta));
            theta += thetaInc;
        Graphics2D g2 = (Graphics2D)image.getGraphics();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.black);
        g2.drawPolyline(xPoints, yPoints, nPoints+1);
        g2.dispose();
        repaint();
    private void initImage() {
        Dimension d = getPreferredSize();
        int w = d.width;
        int h = d.height;
        int type = BufferedImage.TYPE_INT_RGB;
        image = new BufferedImage(w, h, type);
        Graphics2D g2 = image.createGraphics();
        g2.setBackground(getBackground());
        g2.clearRect(0,0,w,h);
        g2.dispose();
    private void start() {
        Thread thread = new Thread(new Runnable() {
            public void run() {
                do {
                    try {
                        Thread.sleep(50);
                    } catch(InterruptedException e) {
                        System.out.println("init interrupted");
                        System.exit(1);
                } while(image == null);
                while(true) {
                    try {
                        Thread.sleep(50);
                    } catch(InterruptedException e) {
                        System.out.println("interrupted");
                        break;
                    draw();
        thread.setPriority(Thread.NORM_PRIORITY);
        thread.start();
    public static void main(String[] args) {
        final SimpleDrawing test = new SimpleDrawing();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new JScrollPane(test));
        f.setSize(500,400);
        f.setLocation(200,200);
        f.setVisible(true);
        test.start();
}