path: root/java/awt/BufferCapabilities.java

/* BufferCapabilities.java -- double-buffering capabilities descriptor
   Copyright (C) 2002, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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permission to link this library with independent modules to produce an
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package java.awt;

/**
 * A double-buffering capability descriptor.  This class exposes
 * details about the double-buffering algorithms used by image
 * buffers.
 *
 * BufferCapabilities represents algorithms that involve at least two
 * buffers but it can also specify so-called "multi-buffer" schemes
 * involving more than two buffers.  This class describes the
 * capabilities of the front and back buffers as well as the results
 * of "flipping" -- that is, what happens when an image is transferred
 * from the back buffer to the front buffer.
 *
 * Flipping may or may not be supported or may be supported only in
 * fullscreen mode.  If it is not supported then "blitting" is implied
 * -- that is, the contents of the back buffer are copied using a fast
 * block transfer operation from the back buffer to the front buffer.
 *
 * The front buffer is the one that is displayed.
 *
 * @author Eric Blake (ebb9@email.byu.edu)
 *
 * @see BufferStrategy#getCapabilities()
 * @see GraphicsConfiguration#getCapabilities()
 *
 * @since 1.4
 */
public class BufferCapabilities implements Cloneable
{
  /**
   * A type-safe enumeration of buffer flipping results.
   *
   * @see AttributeValue
   */
  public static final class FlipContents extends AttributeValue
  {
    /**
     * The names of the different flipping results.
     */
    private static final String[] NAMES
      = { "undefined", "background", "prior", "copied" };

    /**
     * The contents of the back buffer are undefined after flipping.
     */
    public static final FlipContents UNDEFINED = new FlipContents(0);

    /**
     * The back buffer is cleared with the background color after
     * flipping.
     */
    public static final FlipContents BACKGROUND = new FlipContents(1);

    /**
     * The back buffer contains the pre-flipping contents of the front
     * buffer after flipping.  In other words a true "flip" has been
     * performed.
     */
    public static final FlipContents PRIOR = new FlipContents(2);

    /**
     * The back buffer has the same contents as the front buffer after
     * flipping.
     */
    public static final FlipContents COPIED = new FlipContents(3);

    /**
     * Create a new flipping result descriptor.
     *
     * @param value the enumeration value
     */
    private FlipContents(int value)
    {
      super(value, NAMES);
    }
  }

  /**
   * Front buffer capabilities descriptor.
   */
  private final ImageCapabilities front;

  /**
   * Back buffer capabilities descriptor.
   */
  private final ImageCapabilities back;

  /**
   * Describes the results of a "flip" operation.
   */
  private final FlipContents flip;

  /**
   * Creates a buffer capabilities object.
   *
   * @param frontCaps front buffer capabilities descriptor
   * @param backCaps back buffer capabilities descriptor
   * @param flip the results of a flip operation or null if
   * flipping is not supported
   *
   * @exception IllegalArgumentException if frontCaps or backCaps is
   * null
   */
  public BufferCapabilities(ImageCapabilities frontCaps,
			    ImageCapabilities backCaps,
                            FlipContents flip)
  {
    if (frontCaps ==  null || backCaps == null)
      throw new IllegalArgumentException();
    this.front = frontCaps;
    this.back = backCaps;
    this.flip = flip;
  }

  /**
   * Retrieve the front buffer's image capabilities.
   *
   * @return the front buffer's image capabilities
   */
  public ImageCapabilities getFrontBufferCapabilities()
  {
    return front;
  }

  /**
   * Retrieve the back buffer's image capabilities.
   *
   * @return the back buffer's image capabilities
   */
  public ImageCapabilities getBackBufferCapabilities()
  {
    return back;
  }

  /**
   * Return whether or not flipping is supported.
   *
   * @return true if flipping is supported, false otherwise
   */
  public boolean isPageFlipping()
  {
    return flip != null;
  }

  /**
   * Retrieve the result of a flipping operation.  If this method
   * returns null then flipping is not supported.  This implies that
   * "blitting", a fast block transfer, is used to copy the contents
   * of the back buffer to the front buffer.  Other possible return
   * values are:
   * <ul>
   *   <li><code>FlipContents.UNDEFINED</code> the contents of the
   *   back buffer are undefined after flipping.</li>
   *   <li><code>FlipContents.BACKGROUND</code> the contents of the
   *   back buffer are cleared to the background color after
   *   flipping.</li>
   *   <li><code>FlipContents.PRIOR</code> the back buffer contains
   *   the pre-flipping contents of the front * buffer after
   *   flipping.</li>
   *   <li><code>FlipContents.COPIED</code> the back buffer has the
   *   same contents as the front buffer after flipping.</li>
   * </ul>
   *
   * @return the result of a flipping operation or null if flipping is
   * not supported
   */
  public FlipContents getFlipContents()
  {
    return flip;
  }

  /**
   * Returns true if flipping is only supported in fullscreen mode.
   *
   * @return true if flipping is only supported in fullscreen mode,
   * false otherwise
   */
  public boolean isFullScreenRequired()
  {
    return true;
  }

  /**
   * Returns true if flipping can involve more than two buffers.  One
   * or more intermediate buffers may be available in addition to the
   * front and back buffers.
   *
   * @return true if there are more than two buffers available for
   * flipping, false otherwise
   */
  public boolean isMultiBufferAvailable()
  {
    return false;
  }

  /**
   * Clone this buffering capability descriptor.
   *
   * @return a clone of this buffer capability descriptor
   */
  public Object clone()
  {
    try
      {
        return super.clone();
      }
    catch (CloneNotSupportedException e)
      {
        throw (Error) new InternalError().initCause(e);
      }
  }
}