volatileimage.java

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/*
 * @(#)VolatileImage.java	1.15 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.image;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.Image;
import java.awt.ImageCapabilities;
import java.awt.Toolkit;

/**
 * VolatileImage is an image which can lose its 
 * contents at any time due to circumstances beyond the control of the 
 * application (e.g., situations caused by the operating system or by
 * other applications). Because of the potential for hardware acceleration,
 * a VolatileImage object can have significant performance benefits on 
 * some platforms.
 * <p>
 * The drawing surface of an image (the memory where the image contents 
 * actually reside) can be lost or invalidated, causing the contents of that 
 * memory to go away.  The drawing surface thus needs to be restored
 * or recreated and the contents of that surface need to be
 * re-rendered.  VolatileImage provides an interface for 
 * allowing the user to detect these problems and fix them
 * when they occur.
 * <p>
 * This image should not be subclassed directly but should be created
 * by using the {@link java.awt.Component#createVolatileImage(int, int)
 * Component.createVolatileImage} or 
 * {@link java.awt.GraphicsConfiguration#createCompatibleVolatileImage(int, int)
 * GraphicsConfiguration.createCompatibleVolatileImage(int, int)} methods.
 * <P>
 * An example of using a VolatileImage object follows:
 * <pre>
 * // image creation
 * VolatileImage vImg = createVolatileImage(w, h);
 *
 * 
 * // rendering to the image
 * void renderOffscreen() {
 *	do {
 *	    if (vImg.validate(getGraphicsConfiguration()) ==
 *		VolatileImage.IMAGE_INCOMPATIBLE)
 *	    {
 *		// old vImg doesn't work with new GraphicsConfig; re-create it
 *		vImg = createVolatileImage(w, h);
 *	    }
 *	    Graphics2D g = vImg.createGraphics();
 *	    //
 *	    // miscellaneous rendering commands...
 *	    //
 *	    g.dispose();
 *	} while (vImg.contentsLost());
 * }
 *
 *
 * // copying from the image (here, gScreen is the Graphics
 * // object for the onscreen window)
 * do {
 *	int returnCode = vImg.validate(getGraphicsConfiguration());
 *	if (returnCode == VolatileImage.IMAGE_RESTORED) {
 *	    // Contents need to be restored
 *	    renderOffscreen();	    // restore contents
 *	} else if (returnCode == VolatileImage.IMAGE_INCOMPATIBLE) {
 *	    // old vImg doesn't work with new GraphicsConfig; re-create it
 *	    vImg = createVolatileImage(w, h);
 *	    renderOffscreen();
 *	}
 *	gScreen.drawImage(vImg, 0, 0, this);
 * } while (vImg.contentsLost());
 * </pre>
 * <P>
 * Note that this class subclasses from the {@link Image} class, which
 * includes methods that take an {@link ImageObserver} parameter for
 * asynchronous notifications as information is received from
 * a potential {@link ImageProducer}.  Since this <code>VolatileImage</code> 
 * is not loaded from an asynchronous source, the various methods that take
 * an <code>ImageObserver</code> parameter will behave as if the data has
 * already been obtained from the <code>ImageProducer</code>.  
 * Specifically, this means that the return values from such methods 
 * will never indicate that the information is not yet available and 
 * the <code>ImageObserver</code> used in such methods will never 
 * need to be recorded for an asynchronous callback notification.
 */
public abstract class VolatileImage extends Image
{

    // Return codes for validate() method

    /**
     * Validated image is ready to use as-is.
     */
    public static final int IMAGE_OK = 0;

    /**
     * Validated image has been restored and is now ready to use.
     * Note that restoration causes contents of the image to be lost.
     */
    public static final int IMAGE_RESTORED = 1;

    /**
     * Validated image is incompatible with supplied 
     * <code>GraphicsConfiguration</code> object and should be
     * re-created as appropriate.  Usage of the image as-is
     * after receiving this return code from <code>validate</code>
     * is undefined.
     */
    public static final int IMAGE_INCOMPATIBLE = 2;

    /**
     * Returns a static snapshot image of this object.  The
     * <code>BufferedImage</code> returned is only current with
     * the <code>VolatileImage</code> at the time of the request 
     * and will not be updated with any future changes to the 
     * <code>VolatileImage</code>.
     * @return a {@link BufferedImage} representation of this
     *		<code>VolatileImage</code>
     * @see BufferedImage
     */
    public abstract BufferedImage getSnapshot();
    
    /**
     * Returns the width of the <code>VolatileImage</code>.
     * @return the width of this <code>VolatileImage</code>.
     */
    public abstract int getWidth();

    /**
     * Returns the height of the <code>VolatileImage</code>.
     * @return the height of this <code>VolatileImage</code>.
     */
    public abstract int getHeight();

    // Image overrides

    /** 
     * This returns an ImageProducer for this VolatileImage.
     * Note that the VolatileImage object is optimized for 
     * rendering operations and blitting to the screen or other
     * VolatileImage objects, as opposed to reading back the
     * pixels of the image.  Therefore, operations such as
     * <code>getSource</code> may not perform as fast as
     * operations that do not rely on reading the pixels.
     * Note also that the pixel values read from the image are current
     * with those in the image only at the time that they are 
     * retrieved. This method takes a snapshot
     * of the image at the time the request is made and the
     * ImageProducer object returned works with
     * that static snapshot image, not the original VolatileImage.
     * Calling getSource()
     * is equivalent to calling getSnapshot().getSource().
     * @return an {@link ImageProducer} that can be used to produce the
     * pixels for a <code>BufferedImage</code> representation of
     * this Image.
     * @see ImageProducer
     * @see #getSnapshot()
     */
    public ImageProducer getSource() {
	// REMIND: Make sure this functionality is in line with the
	// spec.  In particular, we are returning the Source for a 
	// static image (the snapshot), not a changing image (the 
	// VolatileImage).  So if the user expects the Source to be
	// up-to-date with the current contents of the VolatileImage,
	// they will be disappointed...
	// REMIND: This assumes that getSnapshot() returns something
	// valid and not the default null object returned by this class
	// (so it assumes that the actual VolatileImage object is 
	// subclassed off something that does the right thing 
	// (e.g., SunVolatileImage).
	return getSnapshot().getSource();
    }

    // REMIND: if we want any decent performance for getScaledInstance(),
    // we should override the Image implementation of it...

    /**
     * Releases system resources currently consumed by this image.
     * <p>
     * When a VolatileImage object is created, limited system resources
     * such as video memory (VRAM) may be allocated in order to
     * support the image.  When a VolatileImage object is no longer
     * used, it may be garbage-collected and those system resources
     * will be returned, but this process does 
     * not happen at guaranteed times.  Applications that create
     * many VolatileImage objects (for example, a resizing window
     * may force recreation of its back buffer as the size
     * changes) may run out of optimal system
     * resources for new VolatileImage objects simply because the
     * old objects have not yet been removed from the system.  
     * (New VolatileImage objects may still be created, but they
     * may not perform as well as those created in accelerated
     * memory).
     * <p>
     * By calling this flush method, applications can have more control over
     * the state of the resources taken up by obsolete VolatileImage objects.
     * <p>
     * This method will cause the contents of the image to be lost, so
     * calls to {@link #contentsLost} will return <code>true</code>
     * and the image must be validated before it can be used again.
     * @see #contentsLost
     * @see #validate
     */
    public void flush() {
    }

    /**
     * This method returns a {@link Graphics2D}, but is here
     * for backwards compatibility.  {@link #createGraphics() createGraphics} is more
     * convenient, since it is declared to return a 
     * <code>Graphics2D</code>.
     * @return a <code>Graphics2D</code>, which can be used to draw into
     *          this image.
     */
    public Graphics getGraphics() {
	return createGraphics();
    }

    /**
     * Creates a <code>Graphics2D</code>, which can be used to draw into
     * this <code>VolatileImage</code>.
     * @return a <code>Graphics2D</code>, used for drawing into this
     *          image. 
     */
    public abstract Graphics2D createGraphics();


    // Volatile management methods

    /**
     * Attempts to restore the drawing surface of the image if the surface
     * had been lost since the last <code>validate</code> call.  Also
     * validates this image against the given GraphicsConfiguration
     * parameter to see whether operations from this image to the
     * GraphicsConfiguration are compatible.  An example of an
     * incompatible combination might be a situation where a VolatileImage
     * object was created on one graphics device and then was used
     * to render to a different graphics device.  Since VolatileImage
     * objects tend to be very device-specific, this operation might
     * not work as intended, so the return code from this validate
     * call would note that incompatibility.  A null or incorrect 
     * value for gc may cause incorrect values to be returned from
     * <code>validate</code> and may cause later problems with rendering.
     *
     * @param   gc   a <code>GraphicsConfiguration</code> object for this
     *		image to be validated against.  A null gc implies that the
     *		validate method should skip the compatibility test.
     * @return	<code>IMAGE_OK</code> if the image did not need validation<BR>
     *		<code>IMAGE_RESTORED</code> if the image needed restoration.  
     *		Restoration implies that the contents of the image may have 
     *		been affected and the image may need to be re-rendered.<BR>
     *		<code>IMAGE_INCOMPATIBLE</code> if the image is incompatible
     *		with the <code>GraphicsConfiguration</code> object passed
     *		into the <code>validate</code> method.  Incompatibility
     *		implies that the image may need to be recreated with a
     *		new <code>Component</code> or 
     *		<code>GraphicsConfiguration</code> in order to get an image
     *		that can be used successfully with this 
     *		<code>GraphicsConfiguration</code>.
     *		An incompatible image is not checked for whether restoration
     *		was necessary, so the state of the image is unchanged 
     *		after a return value of <code>IMAGE_INCOMPATIBLE</code>
     *		and this return value implies nothing about whether the
     *		image needs to be restored.
     * @see java.awt.GraphicsConfiguration
     * @see java.awt.Component
     * @see #IMAGE_OK
     * @see #IMAGE_RESTORED
     * @see #IMAGE_INCOMPATIBLE
     */
    public abstract int validate(GraphicsConfiguration gc);

    /**
     * Returns <code>true</code> if rendering data was lost since last 
     * <code>validate</code> call.  This method should be called by the 
     * application at the end of any series of rendering operations to 
     * or from the image to see whether
     * the image needs to be validated and the rendering redone.
     * @return <code>true</code> if the drawing surface needs to be restored;
     * <code>false</code> otherwise.
     */
    public abstract boolean contentsLost();

    /**
     * Returns an ImageCapabilities object which can be
     * inquired as to the specific capabilities of this
     * VolatileImage.  This would allow programmers to find
     * out more runtime information on the specific VolatileImage
     * object that they have created.  For example, the user
     * might create a VolatileImage but the system may have
     * no video memory left for creating an image of that
     * size, so although the object is a VolatileImage, it is
     * not as accelerated as other VolatileImage objects on
     * this platform might be.  The user might want that
     * information to find other solutions to their problem.
     * @return an <code>ImageCapabilities</code> object that contains
     *         the capabilities of this <code>VolatileImage</code>.
     * @since 1.4
     */
    public abstract ImageCapabilities getCapabilities();

}