/**

 *  Apple Worldwide Developer Technical Support

 *

 *  Sample demonstrating offscreen drawing.

 *

 *  by Levi Brown, Apple Developer Technical Support

 *

 *  File:   BufferedDrawer.java

 *

 *  Copyright ©1999 Apple Computer, Inc.

 *  All rights reserved.

 *

 *  4/99    v. 1.0  Shipped as 'Magic Oracle AppleScript for Java' sample.

 *

 *  You may incorporate this sample code into your applications without

 *  restriction, though the sample code has been provided "AS IS" and the

 *  responsibility for its operation is 100% yours.  However, what you are

 *  not permitted to do is to redistribute the source as "Apple Sample

 *  Code" after having made changes. If you're going to re-distribute the

 *  source, we require that you make it clear in the source that the code

 *  was descended from Apple Sample Code, but that you've made changes.

**/

import java.awt.Component;

import java.awt.Image;

import java.awt.Graphics;

import java.awt.Dimension;

/**

 * A component which does all it's drawing in an offscreen image

 * the size of the component.

 *

 * @author Levi Brown

 * @author Apple Worldwide Developer Technical Support

 * @author Apple Computer Inc.

 * @version 1.0 11/4/1998

 */

public class BufferedDrawer extends Component

{

    /**

     * Creates a new BufferedDrawer.

     */

    public BufferedDrawer()

    {

        //Initialize our data members

        workingGraphics     = null;

        workingImage        = null;

    }

    /**

     * Handles drawing the desired content into the offscreen buffer.

     * Override this to do your own drawing (be sure to call super.draw()).

     * @see #paint

     */

    protected void draw()

    {

        //Make sure the offscreen image is ready to be drawn into.

        ensureValidWorkingImage();

        //Do drawing here (use workingGraphics)

        //Don't forget to erase the buffer if you don't draw over the entire area

        //or else you will end up with tracers.

        //To erase the entire area, uncomment out the following code:

        /*

        Dimension s = new Dimension(workingImage.getWidth(this), workingImage.getHeight(this));

        workingGraphics.setColor(getBackground());

        workingGraphics.fillRect(0, 0, s.width, s.height);

        */

    }

    /**

     * Makes sure the offscreen image exists.

     */

    protected void ensureValidWorkingImage()

    {

        //If the size changed and we need to create a new pane image, then create one

        Dimension size = getSize();

        if ((size != null && size.width > 0 && size.height > 0) && (workingImage == null || size.width != workingImage.getWidth(this) || size.height != workingImage.getHeight(this)))

        {

            if (workingImage != null)

            {

                workingImage.flush();

                workingImage = null;

            }

            workingImage = createImage(size.width, size.height);

            if (workingGraphics != null)

            {

                workingGraphics.dispose();

                workingGraphics = null;

            }

            workingGraphics = workingImage == null ? null : workingImage.getGraphics();

        }

    }

    /** 

     * Updates the component. This method is called in

     * response to a call to repaint. You can assume that

     * the background is not cleared.

     * Overriden here to prevent unwanted background erasing.

     * @param g the specified Graphics window

     * @see #paint

     * @see java.awt.Component#repaint

     */

    public void update(Graphics g)

    {

        paint(g);

    }

    /** 

     * Paints the component.  This method is called when the contents

     * of the component should be painted in response to the component

     * first being shown or damage needing repair.  The clip rectangle

     * in the Graphics parameter will be set to the area which needs

     * to be painted.

     * @param g the specified Graphics object

     * @see #update

     */

    public void paint(Graphics g)

    {

        draw();

        g.drawImage(workingImage, 0, 0, this);

    }

    //The offscreen image buffer to render the progress bar into.

    protected Image workingImage;

    //The Graphics object associated with the offscreen image buffer.

    protected Graphics workingGraphics;

}