Double Buffering: Example6Applet

Here is the drawing code for the applet that is shown above. The code for the entire applet can be found in Example6Applet.java.

    Dimension offDimension;
    Image offImage;
    Graphics offGraphics;

    /**
     * Update a frame of animation.
     */
    public void update(Graphics g) {
	Dimension d = size();

	// Create the offscreen graphics context
	if ((offGraphics == null)
	 || (d.width != offDimension.width)
	 || (d.height != offDimension.height)) {
	    offDimension = d;
	    offImage = createImage(d.width, d.height);
	    offGraphics = offImage.getGraphics();
	}

	// Erase the previous image
	offGraphics.setColor(getBackground());
	offGraphics.fillRect(0, 0, d.width, d.height);
	offGraphics.setColor(Color.black);

	// Paint the frame into the image
	paintFrame(offGraphics);

	// Paint the image onto the screen
	g.drawImage(offImage, 0, 0, null);
    }

    /**
     * Paint the previous frame (if any).
     */
    public void paint(Graphics g) {
	if (offImage != null) {
	    g.drawImage(offImage, 0, 0, null);
	}
    }

    /**
     * Paint a frame of animation.
     */
    public void paintFrame(Graphics g) {
	Dimension d = size();
	int h = d.height / 2;
	for (int x = 0 ; x < d.width ; x++) {
	    int y1 = (int)((1.0 + Math.sin((x - frame) * 0.05)) * h);
	    int y2 = (int)((1.0 + Math.sin((x + frame) * 0.07)) * h);
	    g.drawLine(x, y1, x, y2);
	}
    }