java.lang.Object | ||
↳ | java.awt.Image | |
↳ | java.awt.image.VolatileImage |
Known Direct Subclasses |
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.
Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
int | IMAGE_INCOMPATIBLE | Validated image is incompatible with supplied
GraphicsConfiguration object and should be
re-created as appropriate. |
|||||||||
int | IMAGE_OK | Validated image is ready to use as-is. | |||||||||
int | IMAGE_RESTORED | Validated image has been restored and is now ready to use. |
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Inherited Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.awt.Image
| |||||||||||
From interface
java.awt.Transparency
|
Fields | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
transparency | The transparency value with which this image was created. |
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Inherited Fields | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.awt.Image
|
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Returns
true if rendering data was lost since last
validate call. | |||||||||||
Creates a
Graphics2D , which can be used to draw into
this VolatileImage . | |||||||||||
Returns an ImageCapabilities object which can be
inquired as to the specific capabilities of this
VolatileImage.
| |||||||||||
This method returns a
Graphics2D , but is here
for backwards compatibility. | |||||||||||
Returns the height of the
VolatileImage . | |||||||||||
Returns a static snapshot image of this object.
| |||||||||||
This returns an ImageProducer for this VolatileImage.
| |||||||||||
Returns the transparency.
| |||||||||||
Returns the width of the
VolatileImage . | |||||||||||
Attempts to restore the drawing surface of the image if the surface
had been lost since the last
validate call. |
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.awt.Image
| |||||||||||
From class
java.lang.Object
| |||||||||||
From interface
java.awt.Transparency
|
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 ready to use as-is.
Validated image has been restored and is now ready to use. Note that restoration causes contents of the image to be lost.
The transparency value with which this image was created.
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.
true
if the drawing surface needs to be restored;
false
otherwise.
Creates a Graphics2D
, which can be used to draw into
this VolatileImage
.
Graphics2D
, used for drawing into this
image.
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.
ImageCapabilities
object that contains
the capabilities of this VolatileImage
.This method returns a Graphics2D
, but is here
for backwards compatibility. createGraphics
is more
convenient, since it is declared to return a
Graphics2D
.
Graphics2D
, which can be used to draw into
this image.
Returns the height of the VolatileImage
.
VolatileImage
.
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
.
BufferedImage
representation of this
VolatileImage
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().
ImageProducer
that can be used to produce the
pixels for a BufferedImage
representation of
this Image.Returns the transparency. Returns either OPAQUE, BITMASK, or TRANSLUCENT.
VolatileImage
.Returns the width of the VolatileImage
.
VolatileImage
.
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.
gc | a GraphicsConfiguration object for this
image to be validated against. A null gc implies that the
validate method should skip the compatibility test. |
---|
IMAGE_OK
if the image did not need validationIMAGE_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.