- java.lang.Object
-
- java.awt.image.BufferStrategy
-
- Direct Known Subclasses:
- Component.BltBufferStrategy, Component.FlipBufferStrategy
public abstract class BufferStrategy extends Object
TheBufferStrategy
class represents the mechanism with which to organize complex memory on a particularCanvas
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
orWindow
.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:
Window
,Canvas
,GraphicsConfiguration
,VolatileImage
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-
Constructor Summary
Constructors Constructor and Description BufferStrategy()
-
Method Summary
Methods Modifier and Type Method and Description abstract boolean
contentsLost()
Returns whether the drawing buffer was lost since the last call togetDrawGraphics
.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 thisBufferStrategy
and removes it from the associated Component.abstract BufferCapabilities
getCapabilities()
Returns theBufferCapabilities
for thisBufferStrategy
.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).
-
-
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Method Detail
-
getCapabilities
public abstract BufferCapabilities getCapabilities()
Returns theBufferCapabilities
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 typeVolatileImage
, they may become lost. For a discussion on lost buffers, seeVolatileImage
.- 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, seeVolatileImage
.- 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 aBufferStrategy
after it has been disposed will result in undefined behavior.
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