java.awt.image

Class VolatileImage

java.lang.Object

java.awt.Image

java.awt.image.VolatileImage

public abstract class VolatileImage
extends Image

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.

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.

Field Summary

Fields

Modifier and Type	Field and Description
static int	IMAGE_INCOMPATIBLE Validated image is incompatible with supplied GraphicsConfiguration object and should be re-created as appropriate.
static int	IMAGE_OK Validated image is ready to use as-is.
static int	IMAGE_RESTORED Validated image has been restored and is now ready to use.

Fields inherited from class java.awt.Image

SCALE_AREA_AVERAGING, SCALE_DEFAULT, SCALE_FAST, SCALE_REPLICATE, SCALE_SMOOTH, UndefinedProperty

Constructor Summary

Constructors

Constructor and Description
VolatileImage()

Method Summary

Methods

Modifier and Type	Method and Description
abstract boolean	contentsLost() Returns true if rendering data was lost since last validate call.
abstract Graphics2D	createGraphics() Creates a Graphics2D, which can be used to draw into this VolatileImage.
void	flush() Releases system resources currently consumed by this image.
abstract ImageCapabilities	getCapabilities() Returns an ImageCapabilities object which can be inquired as to the specific capabilities of this VolatileImage.
Graphics	getGraphics() This method returns a Graphics2D, but is here for backwards compatibility.
abstract int	getHeight() Returns the height of the VolatileImage.
abstract BufferedImage	getSnapshot() Returns a static snapshot image of this object.
ImageProducer	getSource() This returns an ImageProducer for this VolatileImage.
abstract int	getWidth() Returns the width of the VolatileImage.
abstract int	validate(GraphicsConfiguration gc) Attempts to restore the drawing surface of the image if the surface had been lost since the last validate call.

Methods inherited from class java.awt.Image

getHeight, getProperty, getScaledInstance, getWidth

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

IMAGE_OK

public static final int IMAGE_OK

Validated image is ready to use as-is.

See Also:

Constant Field Values

IMAGE_RESTORED

public static final int IMAGE_RESTORED

Validated image has been restored and is now ready to use. Note that restoration causes contents of the image to be lost.

See Also:

Constant Field Values

IMAGE_INCOMPATIBLE

public static final int IMAGE_INCOMPATIBLE

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.

See Also:

Constant Field Values

Constructor Detail

VolatileImage

public VolatileImage()

Method Detail

getSnapshot

public abstract BufferedImage getSnapshot()

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.

Returns:

a BufferedImage representation of this VolatileImage

See Also:

BufferedImage

getWidth

public abstract int getWidth()

Returns the width of the VolatileImage.

Returns:

the width of this VolatileImage.

getHeight

public abstract int getHeight()

Returns the height of the VolatileImage.

Returns:

the height of this VolatileImage.

getSource

public ImageProducer getSource()

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().

Specified by:

getSource in class Image

Returns:

an ImageProducer that can be used to produce the pixels for a BufferedImage representation of this Image.

See Also:

ImageProducer, getSnapshot()

flush

public void flush()

Releases system resources currently consumed by this image.

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).

By calling this flush method, applications can have more control over the state of the resources taken up by obsolete VolatileImage objects.

This method will cause the contents of the image to be lost, so calls to contentsLost() will return true and the image must be validated before it can be used again.

Specified by:

flush in class Image

See Also:

contentsLost(), validate(java.awt.GraphicsConfiguration)

getGraphics

public Graphics getGraphics()

This method returns a Graphics2D, but is here for backwards compatibility. createGraphics is more convenient, since it is declared to return a Graphics2D.

Specified by:

getGraphics in class Image

Returns:

a Graphics2D, which can be used to draw into this image.

See Also:

Graphics, Component.createImage(int, int)

createGraphics

public abstract Graphics2D createGraphics()

Creates a Graphics2D, which can be used to draw into this VolatileImage.

Returns:

a Graphics2D, used for drawing into this image.

validate

public abstract int validate(GraphicsConfiguration gc)

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.

Parameters:

gc - a GraphicsConfiguration object for this image to be validated against. A null gc implies that the validate method should skip the compatibility test.

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.

See Also:

GraphicsConfiguration, Component, IMAGE_OK, IMAGE_RESTORED, IMAGE_INCOMPATIBLE

contentsLost

public abstract boolean contentsLost()

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.

getCapabilities

public abstract ImageCapabilities getCapabilities()

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