001 /* BufferStrategy.java -- describes image buffering resources
002 Copyright (C) 2002, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
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007 it under the terms of the GNU General Public License as published by
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020
021 Linking this library statically or dynamically with other modules is
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036 exception statement from your version. */
037
038
039 package java.awt.image;
040
041 import java.awt.BufferCapabilities;
042 import java.awt.Graphics;
043
044 /**
045 * This class describes a strategy for managing image buffering
046 * resources on a Canvas or Window. A given buffer strategy may make
047 * use of hardware acceleration or take advantage of features of the
048 * native graphics system. Examples of buffering strategies are
049 * double or triple buffering using either flipping or blitting. For
050 * the details of these algorithms see BufferCapabilities.
051 *
052 * To use a buffer strategy, you retrieve it from either the current
053 * GraphicsConfiguration or from the Component on which you'd like to
054 * draw. Then you can query the strategy's capabilities to make sure
055 * they're suitable.
056 *
057 * If the strategy's capabilities are suitable, you can obtain a
058 * graphics object and use it to draw with this strategy. Drawing
059 * with a buffer strategy requires extra care, however. You'll need
060 * to manually cause the next buffer to be shown on the output device.
061 * And since buffer strategies are usually implemented with a
062 * VolatileImage, you must frequently check that the contents of the
063 * buffer are valid and that the buffer still exists.
064 *
065 * A buffer strategy is usually implemented using a VolatileImage.
066 *
067 * @see VolatileImage
068 * @since 1.4
069 */
070 public abstract class BufferStrategy
071 {
072 /**
073 * Creates a new buffer strategy.
074 */
075 public BufferStrategy()
076 {
077 }
078
079 /**
080 * Retrieves the capabilities of this buffer strategy.
081 *
082 * @return this buffer strategy's capabilities
083 */
084 public abstract BufferCapabilities getCapabilities();
085
086 /**
087 * Retrieves a graphics object that can be used to draw using this
088 * buffer strategy. This method may not be synchronized so be
089 * careful when calling it from multiple threads. You also must
090 * manually dispose of this graphics object.
091 *
092 * @return a graphics object that can be used to draw using this
093 * buffer strategy
094 */
095 public abstract Graphics getDrawGraphics();
096
097 /**
098 * Returns whether or not the buffer's resources have been reclaimed
099 * by the native graphics system. If the buffer resources have been
100 * lost then you'll need to obtain new resources before drawing
101 * again. For details, see the documentation for VolatileImage.
102 *
103 * @return true if the contents were lost, false otherwise
104 */
105 public abstract boolean contentsLost();
106
107 /**
108 * Returns whether or not the buffer's resources were re-created and
109 * cleared to the default background color. If the buffer's
110 * resources have recently been re-created and initialized then the
111 * buffer's image may need to be re-rendered. For details, see the
112 * documentation for VolatileImage.
113 *
114 * @return true if the contents were restored, false otherwise
115 */
116 public abstract boolean contentsRestored();
117
118 /**
119 * Applies this buffer strategy. In other words, this method brings
120 * the contents of the back or intermediate buffers to the front
121 * buffer.
122 */
123 public abstract void show();
124 }