BufferStrategy (Java Platform SE 6) (original) (raw)

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 orWindow. Hardware and software limitations determine whether and how a particular buffer strategy can be implemented. These limitations are detectible through the capabilities of theGraphicsConfiguration used when creating theCanvas 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 sequential ring buffering and blit buffering. 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 * * <------ * * <----- * * *********** *********** ***********

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();

 // Main loop
 while (!done) {
     // Prepare for rendering the next frame
     // ...

     // Render single frame
     do {
         // The following loop ensures that the contents of the drawing buffer
         // are consistent in case the underlying surface was recreated
         do {
             // Get a new graphics context every time through the loop
             // to make sure the strategy is validated
             Graphics graphics = strategy.getDrawGraphics();
     
             // Render to graphics
             // ...

             // Dispose the graphics
             graphics.dispose();

             // Repeat the rendering if the drawing buffer contents 
             // were restored
         } while (strategy.contentsRestored());

         // Display the buffer
         strategy.show();

         // Repeat the rendering if the drawing buffer was lost
     } while (strategy.contentsLost());
 }

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

Since:

1.4

See Also:

Component, GraphicsConfiguration, VolatileImage

BufferStrategy

public BufferStrategy()

getCapabilities

public abstract BufferCapabilities getCapabilities()

Returns the BufferCapabilities for thisBufferStrategy.

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

contentsLost

public abstract boolean contentsLost()

Returns whether the drawing buffer was lost since the last call togetDrawGraphics. 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 typeVolatileImage, they may become lost. If a surface has been recently restored from a lost state since the last call togetDrawGraphics, 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 thisBufferStrategy 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(int), Component.getBufferStrategy()

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

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