Off Screen Buffers

The second and often more effective method to avoid flicker is to use offscreen images and the update() method. By overriding the update() method you can do all your painting in an offscreen Image, and then just copy the final Image onto the screen. Copying an image happens much more quickly and evenly than painting individual elements so there's no visible flicker.

The cookbook approach is simple. Add the following three private fields to your applet and the public update() method. Flicker will magically disappear.

  private Image     offScreenImage;
  private Dimension offScreenSize;
  private Graphics  offScreenGraphics;

  public final synchronized void update (Graphics g) {

    Dimension d = this.getSize();
    if((this.offScreenImage == null)
     || (d.width != this.offScreenSize.width) 
     ||  (d.height != this.offScreenSize.height)) {
      this.offScreenImage = this.createImage(d.width, d.height);
      this.offScreenSize = d;
      this.offScreenGraphics = this.offScreenImage.getGraphics();
    this.offScreenGraphics.clearRect(0, 0, d.width, d.height);
    g.drawImage(this.offScreenImage, 0, 0, null);

Bouncing ball
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Copyright 1997, 1998, 2006 Elliotte Rusty Harold
Last Modified August 22, 2006