001/* BufferStrategy.java -- describes image buffering resources 002 Copyright (C) 2002, 2005 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package java.awt.image; 040 041import java.awt.BufferCapabilities; 042import 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 */ 070public 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}