java.awt.image
Class BufferStrategy

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

Direct Known Subclasses:

Component.BltBufferStrategy , Component.FlipBufferStrategy

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, including strategies; sequential ring buffering, blit buffering, and stereo buffering and blit 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();
 // Call this each time through to see if the underlying surface
 // was recreated. If it was you may need to redraw.
 if (strategy.contentsRestored()) {
 // Surface was recreated and reset, may require redrawing.
 }
 // Draw to graphics
 ...
 strategy.show();
 if (strategy.contentsLost()) {
 // The surface was lost since last call to getDrawGraphics, you
 // may need to redraw.
 }
 }

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

Since:

1.4

See Also:

Component , GraphicsConfiguration , VolatileImage

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).
void	dispose ()           Releases system resources currently consumed by this BufferStrategy and removes it from the associated Component.
abstract   BufferCapabilities	getCapabilities ()
abstract   BufferCapabilities Graphics	getCapabilities getDrawGraphics ()           Returns the BufferCapabilities for this BufferStrategy.
abstract   Graphics	getDrawGraphics ()           Creates a graphics context for the drawing buffer.
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()

getCapabilities

public abstract BufferCapabilities getCapabilities()

Returns the BufferCapabilities for this BufferStrategy.

Returns:

the buffering capabilities of this strategy

getDrawGraphics

public abstract Graphics getDrawGraphics()

Creates a graphics context for 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.

Returns:

a graphics context for the drawing buffer 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.

Returns:

Whether or not the drawing buffer was lost since the last call to getDrawGraphics.

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.

Returns:

Whether or not the drawing buffer was restored since the last call to getDrawGraphics.

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).

dispose

 
public void dispose () 

Releases system resources currently consumed by this BufferStrategy and removes it from the associated Component. After invoking this method, getBufferStrategy will return null. Trying to use a BufferStrategy after it has been disposed will result in undefined behavior.

Since:

1.6

See Also:

Component#createBufferStrategy, Component#getBufferStrategy