Java tutorial
/* * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.awt.image; import java.awt.BufferCapabilities; import java.awt.Graphics; import java.awt.Image; /** * The {@code BufferStrategy} class represents the mechanism with which * to organize complex memory on a particular {@code Canvas} or * {@code Window}. Hardware and software limitations determine whether and * how a particular buffer strategy can be implemented. These limitations * are detectable through the capabilities of the * {@code GraphicsConfiguration} used when creating the * {@code Canvas} or {@code Window}. * <p> * It is worth noting that the terms <i>buffer</i> and <i>surface</i> are meant * to be synonymous: an area of contiguous memory, either in video device * memory or in system memory. * <p> * 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 <i>back * buffer</i> 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 <i>front buffer</i>, or what is currently displayed on the * device; this is called <i>page flipping</i>. * <p> * Alternatively, the contents of the back buffer can be copied, or * <i>blitted</i> forward in a chain instead of moving the video pointer. * <pre>{@code * Double buffering: * * *********** *********** * * * ------> * * * [To display] <---- * Front B * Show * Back B. * <---- Rendering * * * <------ * * * *********** *********** * * Triple buffering: * * [To *********** *********** *********** * display] * * --------+---------+------> * * * <---- * Front B * Show * Mid. B. * * Back B. * <---- Rendering * * * <------ * * <----- * * * *********** *********** *********** * * }</pre> * <p> * Here is an example of how buffer strategies can be created and used: * <pre><code> * * // 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(); * </code></pre> * * @see java.awt.Window * @see java.awt.Canvas * @see java.awt.GraphicsConfiguration * @see VolatileImage * @author Michael Martak * @since 1.4 */ public abstract class BufferStrategy { /** * Returns the {@code BufferCapabilities} for this * {@code BufferStrategy}. * * @return the buffering capabilities of this strategy */ public abstract BufferCapabilities getCapabilities(); /** * 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. * * @return a graphics context for the drawing buffer */ public abstract Graphics getDrawGraphics(); /** * Returns whether the drawing buffer was lost since the last call to * {@code getDrawGraphics}. Since the buffers in a buffer strategy * are usually type {@code VolatileImage}, they may become lost. * For a discussion on lost buffers, see {@code VolatileImage}. * * @return Whether or not the drawing buffer was lost since the last call * to {@code getDrawGraphics}. * @see java.awt.image.VolatileImage */ public abstract boolean contentsLost(); /** * 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 type * {@code VolatileImage}, they may become lost. If a surface has * been recently restored from a lost state since the last call to * {@code getDrawGraphics}, it may require repainting. * For a discussion on lost buffers, see {@code VolatileImage}. * * @return Whether or not the drawing buffer was restored since the last * call to {@code getDrawGraphics}. * @see java.awt.image.VolatileImage */ public abstract boolean contentsRestored(); /** * Makes the next available buffer visible by either copying the memory * (blitting) or changing the display pointer (flipping). */ public abstract void show(); /** * Releases system resources currently consumed by this * {@code BufferStrategy} and * removes it from the associated Component. After invoking this * method, {@code getBufferStrategy} will return null. Trying * to use a {@code BufferStrategy} after it has been disposed will * result in undefined behavior. * * @see java.awt.Window#createBufferStrategy * @see java.awt.Canvas#createBufferStrategy * @see java.awt.Window#getBufferStrategy * @see java.awt.Canvas#getBufferStrategy * @since 1.6 */ public void dispose() { } }