BufferStrategy (Java 2 Platform SE v1.4.1_"07")

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JavaTM 2 Platform
Std. Ed. v1.4.1_"07"

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## 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; 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
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).

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JavaTM 2 Platform
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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.