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    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
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    }