java.awt.image
Class BufferStrategy

java.lang.Object
  java.awt.image.BufferStrategy

Direct Known Subclasses:

Component.BltBufferStrategy, Component.FlipBufferStrategy, Component.SingleBufferStrategy

public abstract class BufferStrategy

extends Object

The BufferStrategy class represents the mechanism with which to organize complex memory on a particular Canvas or Window. Hardware and software limitations determine whether and how a particular buffer strategy can be implemented. These limitations are detectible through the capabilities of the GraphicsConfiguration used when creating the Canvas or Window.

It is worth noting that the terms buffer and surface are meant to be synonymous: an area of contiguous memory, either in video device memory or in system memory.

There are several types of complex buffer strategies; sequential ring buffering, blit buffering, and stereo buffering are common types. Sequential ring buffering (i.e., double or triple buffering) is the most common; an application draws to a single back buffer and then moves the contents to the front (display) in a single step, either by copying the data or moving the video pointer. Moving the video pointer exchanges the buffers so that the first buffer drawn becomes the front buffer, or what is currently displayed on the device; this is called page flipping.

Alternatively, the contents of the back buffer can be copied, or blitted forward in a chain instead of moving the video pointer.

 Double buffering:

                    ***********         ***********
                    *         * ------> *         *
 [To display] <---- * Front B *   Show  * Back B. * <---- Rendering
                    *         * <------ *         *
                    ***********         ***********

 Triple buffering:

 [To      ***********         ***********        ***********
 display] *         * --------+---------+------> *         *
    <---- * Front B *   Show  * Mid. B. *        * Back B. * <---- Rendering
          *         * <------ *         * <----- *         *
          ***********         ***********        ***********

 

Stereo buffering is for hardware that supports rendering separate images for a left and right eye. It is similar to sequential ring buffering, but there are two buffer chains, one for each eye. Both buffer chains flip simultaneously:

 Stereo buffering:

                     ***********         ***********
                     *         * ------> *         *
 [To left eye] <---- * Front B *         * Back B. * <---- Rendering
                     *         * <------ *         *
                     ***********         ***********
                                  Show
                     ***********         ***********
                     *         * ------> *         *
 [To right eye] <--- * Front B *         * Back B. * <---- Rendering
                     *         * <------ *         *
                     ***********         ***********
 

Here is an example of how buffer strategies can be created and used:

 // Check the capabilities of the GraphicsConfiguration
 ...

 // Create our component
 Window w = new Window(gc);

 // Show our window
 w.setVisible(true);

 // Create a general double-buffering strategy
 w.createBufferStrategy(2);
 BufferStrategy strategy = w.getBufferStrategy();

 // Render loop
 while (!done) {
    Graphics g = strategy.getDrawGraphics();
    // Draw to graphics
    ...
    strategy.show();
 }

 // Dispose the window
 w.setVisible(false);
 w.dispose();
 

Since:

1.4

Author:

Michael Martak

See Also:

Component, GraphicsConfiguration

Constructor Summary

BufferStrategy()

Method Summary

abstract boolean	contentsLost() Returns whether the drawing buffer was lost since the last call to getDrawGraphics.
abstract boolean	contentsRestored() Returns whether the drawing buffer was recently restored from a lost state and reinitialized to the default background color (white).
abstract BufferCapabilities	getCapabilities()
abstract Graphics	getDrawGraphics()
abstract void	show() Makes the next available buffer visible by either copying the memory (blitting) or changing the display pointer (flipping).

Methods inherited from class java.lang.Object

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

Constructor Detail

BufferStrategy

public BufferStrategy()

Method Detail

getCapabilities

public abstract BufferCapabilities getCapabilities()

Returns:

the buffering capabilities of this strategy

getDrawGraphics

public abstract Graphics getDrawGraphics()

Returns:

the graphics on the drawing buffer. This method may not be synchronized for performance reasons; use of this method by multiple threads should be handled at the application level. Disposal of the graphics object obtained must be handled by the application.

contentsLost

public abstract boolean contentsLost()

Returns whether the drawing buffer was lost since the last call to getDrawGraphics. Since the buffers in a buffer strategy are usually type VolatileImage, they may become lost. For a discussion on lost buffers, see VolatileImage.

See Also:

VolatileImage

contentsRestored

public abstract boolean contentsRestored()

Returns whether the drawing buffer was recently restored from a lost state and reinitialized to the default background color (white). Since the buffers in a buffer strategy are usually type VolatileImage, they may become lost. If a surface has been recently restored from a lost state since the last call to getDrawGraphics, it may require repainting. For a discussion on lost buffers, see VolatileImage.

See Also:

VolatileImage

show

public abstract void show()

Makes the next available buffer visible by either copying the memory (blitting) or changing the display pointer (flipping).