Re: Drawing problem

"Knute Johnson" <knute.johnson@THRWHITE.remove-dii-this>
Wed, 27 Apr 2011 15:31:25 GMT
Michael Rauscher wrote:

Robert Sturzenegger wrote:

I would like to draw a graph in a container. Since the calculation
of the graph may be very time consuming, I would like to watch how
the graph builds up.

Michael Rauscher wrote:

If it's just for testing purposes, you could turn off Swing's double
buffering. Otherwise Andrew Thompson's method is much preferred.

[Andrew Thompson suggested to remove the time consuming task from the EDT].

Robert Sturzenegger wrote:

I tried this and it really accomplishes what I want. Since you stated,
that this solution should be for testing purposes only and that Andrew
Thompson's method would be the preferred one, I also wanted to try his
way. However I failed .... Details can be found in a response to his

The key is to separate the 'current state' of the drawing from the
drawing process.

E.g. you might want to use a BufferedImage as offscreen image.
paintComponent simply draws that image on screen.

private BufferedImage img = new BufferedImage(400, 400,

public void paintComponent( Graphics g ) {
    g.drawImage( img, 0, 0, null );

In theory, you could now manipulate the image and call repaint to show
the result on screen. In practice, this is possible, too. The only thing
you'd have to care of, is to manipulate the image on the EDT.


private void calculateAndPaint() {
    for ( int x = 0; x < 200; ++x ) {
        final int i = x;
        SwingUtilities.invokeLater( new Runnable() {
            public void run() {
                Graphics g = img.createGraphics();
                g.drawLine( i, i, i-1, i-1 );
        try { Thread.sleep(10); } catch ( InterruptedException e ) {}

The last thing one has to do is to let calculateAndPaint be run on a new

public void paint() {
    Thread t = new Thread( new Runnable() {
        public void run() {
    t.setPriority( Thread.NORM_PRIORITY );


There is no requirement that repaint() or graphics calls be made on the EDT.

I wouldn't use paint() as the name of the method because you might
interfere with normal painting.


Knute Johnson
email s/nospam/knute/

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