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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;
import java.awt.Transparency;


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.


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.


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).
The flush method may be called at any time to proactively release
the resources used by a VolatileImage so that it does not prevent
subsequent VolatileImage objects from being accelerated.
In this way, applications can have more control over the state
of the resources taken up by obsolete VolatileImage objects.

 This image should not be subclassed directly but should be created by using the 
Component.createVolatileImage or 
GraphicsConfiguration.createCompatibleVolatileImage(int, int) methods. 

An example of using a VolatileImage object follows:

// 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());



 Note that this class subclasses from the Image class, which includes methods that take an ImageObserver parameter for asynchronous notifications as information is received from a potential ImageProducer. Since this VolatileImage is not loaded from an asynchronous source, the various methods that take an ImageObserver parameter will behave as if the data has already been obtained from the ImageProducer. Specifically, this means that the return values from such methods will never indicate that the information is not yet available and the ImageObserver used in such methods will never need to be recorded for an asynchronous callback notification. 
Since:1.4
/**
 * 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>
 * 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).
 * The flush method may be called at any time to proactively release
 * the resources used by a VolatileImage so that it does not prevent
 * subsequent VolatileImage objects from being accelerated.
 * In this way, applications can have more control over the state
 * of the resources taken up by obsolete VolatileImage objects.
 * <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}
 * is not loaded from an asynchronous source, the various methods that take
 * an {@code ImageObserver} parameter will behave as if the data has
 * already been obtained from the {@code ImageProducer}.
 * Specifically, this means that the return values from such methods
 * will never indicate that the information is not yet available and
 * the {@code ImageObserver} used in such methods will never
 * need to be recorded for an asynchronous callback notification.
 * @since 1.4
 */
public abstract class VolatileImage extends Image implements Transparency
{

    // Return codes for validate() method

    
Validated image is ready to use as-is.

/**
     * 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.

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

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

    
Returns the width of the VolatileImage. 
Returns:the width of this VolatileImage.
/**
     * Returns the width of the {@code VolatileImage}.
     * @return the width of this {@code VolatileImage}.
     */
    public abstract int getWidth();

    
Returns the height of the VolatileImage. 
Returns:the height of this VolatileImage.
/**
     * Returns the height of the {@code VolatileImage}.
     * @return the height of this {@code VolatileImage}.
     */
    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 getSource 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(). 
See Also:
Returns:an ImageProducer that can be used to produce the pixels for a BufferedImage representation of this Image.
/**
     * 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} 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} 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...

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

    
Creates a Graphics2D, which can be used to draw into this VolatileImage. 
Returns:a Graphics2D, used for drawing into this image.
/**
     * Creates a {@code Graphics2D}, which can be used to draw into
     * this {@code VolatileImage}.
     * @return a {@code Graphics2D}, 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 validate 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 validate and may cause later problems with rendering. 
Params:
  • gc –  a GraphicsConfiguration object for this image to be validated against. A null gc implies that the validate method should skip the compatibility test.
See Also:
Returns: IMAGE_OK if the image did not need validation
 IMAGE_RESTORED 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.
 IMAGE_INCOMPATIBLE if the image is incompatible with the GraphicsConfiguration object passed into the validate method. Incompatibility implies that the image may need to be recreated with a new Component or GraphicsConfiguration in order to get an image that can be used successfully with this GraphicsConfiguration. An incompatible image is not checked for whether restoration was necessary, so the state of the image is unchanged after a return value of IMAGE_INCOMPATIBLE and this return value implies nothing about whether the image needs to be restored.
/**
     * Attempts to restore the drawing surface of the image if the surface
     * had been lost since the last {@code validate} 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} and may cause later problems with rendering.
     *
     * @param   gc   a {@code GraphicsConfiguration} 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} if the image did not need validation<BR>
     *          {@code IMAGE_RESTORED} 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} if the image is incompatible
     *          with the {@code GraphicsConfiguration} object passed
     *          into the {@code validate} method.  Incompatibility
     *          implies that the image may need to be recreated with a
     *          new {@code Component} or
     *          {@code GraphicsConfiguration} in order to get an image
     *          that can be used successfully with this
     *          {@code GraphicsConfiguration}.
     *          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}
     *          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 true if rendering data was lost since last validate 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. 
Returns:true if the drawing surface needs to be restored; false otherwise.
/**
     * Returns {@code true} if rendering data was lost since last
     * {@code validate} 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} if the drawing surface needs to be restored;
     * {@code false} 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.

Returns:an ImageCapabilities object that contains the capabilities of this VolatileImage.
Since:1.4
/**
     * 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} object that contains
     *         the capabilities of this {@code VolatileImage}.
     * @since 1.4
     */
    public abstract ImageCapabilities getCapabilities();

    
The transparency value with which this image was created.

See Also:
Since:1.5
/**
     * The transparency value with which this image was created.
     * @see java.awt.GraphicsConfiguration#createCompatibleVolatileImage(int,
     *      int,int)
     * @see java.awt.GraphicsConfiguration#createCompatibleVolatileImage(int,
     *      int,ImageCapabilities,int)
     * @see Transparency
     * @since 1.5
     */
    protected int transparency = TRANSLUCENT;

    
Returns the transparency.  Returns either OPAQUE, BITMASK,
or TRANSLUCENT.

See Also:
Returns:the transparency of this VolatileImage.
Since:1.5
/**
     * Returns the transparency.  Returns either OPAQUE, BITMASK,
     * or TRANSLUCENT.
     * @return the transparency of this {@code VolatileImage}.
     * @see Transparency#OPAQUE
     * @see Transparency#BITMASK
     * @see Transparency#TRANSLUCENT
     * @since 1.5
     */
    public int getTransparency() {
        return transparency;
    }
}