/* * Copyright (c) 2000, 2020, 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}. *
* It is worth noting that the terms buffer and surface are meant * to be synonymous: an area of contiguous memory, either in video device * memory or in system memory. *
* 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 back * buffer 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 front buffer, or what is currently displayed on the * device; this is called page flipping. *
* Alternatively, the contents of the back buffer can be copied, or * blitted forward in a chain instead of moving the video pointer. *
{@code * Double buffering: * * *********** *********** * * * ------> * * * [To display] <---- * Front B * Show * Back B. * <---- Rendering * * * <------ * * * *********** *********** * * Triple buffering: * * [To *********** *********** *********** * display] * * --------+---------+------> * * * <---- * Front B * Show * Mid. B. * * Back B. * <---- Rendering * * * <------ * * <----- * * * *********** *********** *********** * * }*
* Here is an example of how buffer strategies can be created and used: *
*
* // 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();
*
*
* @see java.awt.Window
* @see java.awt.Canvas
* @see java.awt.GraphicsConfiguration
* @see VolatileImage
* @author Michael Martak
* @since 1.4
*/
public abstract class BufferStrategy {
/**
* Creates a {@code BufferStrategy}.
*/
protected 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() {
}
}