/* BufferStrategy.java -- describes image buffering resources
   Copyright (C) 2002, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.awt.image;

import java.awt.BufferCapabilities;
import java.awt.Graphics;

/**
 * This class describes a strategy for managing image buffering
 * resources on a Canvas or Window.  A given buffer strategy may make
 * use of hardware acceleration or take advantage of features of the
 * native graphics system.  Examples of buffering strategies are
 * double or triple buffering using either flipping or blitting.  For
 * the details of these algorithms see BufferCapabilities.
 *
 * To use a buffer strategy, you retrieve it from either the current
 * GraphicsConfiguration or from the Component on which you'd like to
 * draw.  Then you can query the strategy's capabilities to make sure
 * they're suitable.
 *
 * If the strategy's capabilities are suitable, you can obtain a
 * graphics object and use it to draw with this strategy.  Drawing
 * with a buffer strategy requires extra care, however.  You'll need
 * to manually cause the next buffer to be shown on the output device.
 * And since buffer strategies are usually implemented with a
 * VolatileImage, you must frequently check that the contents of the
 * buffer are valid and that the buffer still exists.
 *
 * A buffer strategy is usually implemented using a VolatileImage.
 *
 * @see VolatileImage
 * @since 1.4
 */
public abstract class BufferStrategy
{
  /**
   * Creates a new buffer strategy.
   */
  public BufferStrategy()
  {
  }

  /**
   * Retrieves the capabilities of this buffer strategy.
   *
   * @return this buffer strategy's capabilities
   */
  public abstract BufferCapabilities getCapabilities();

  /**
   * Retrieves a graphics object that can be used to draw using this
   * buffer strategy.  This method may not be synchronized so be
   * careful when calling it from multiple threads.  You also must
   * manually dispose of this graphics object.
   *
   * @return a graphics object that can be used to draw using this
   * buffer strategy
   */
  public abstract Graphics getDrawGraphics();

  /**
   * Returns whether or not the buffer's resources have been reclaimed
   * by the native graphics system.  If the buffer resources have been
   * lost then you'll need to obtain new resources before drawing
   * again.  For details, see the documentation for VolatileImage.
   *
   * @return true if the contents were lost, false otherwise
   */
  public abstract boolean contentsLost();

  /**
   * Returns whether or not the buffer's resources were re-created and
   * cleared to the default background color.  If the buffer's
   * resources have recently been re-created and initialized then the
   * buffer's image may need to be re-rendered.  For details, see the
   * documentation for VolatileImage.
   *
   * @return true if the contents were restored, false otherwise
   */
  public abstract boolean contentsRestored();

  /**
   * Applies this buffer strategy.  In other words, this method brings
   * the contents of the back or intermediate buffers to the front
   * buffer.
   */
  public abstract void show();
}