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* fix: #2223 modify README.md file under double-buffer add - Real world example - In plain words - Wikipedia says - Programmatic example * fix: #2223 issue. modify readme.md file - adjust title, category, language, and tag
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Md Saiful Islam
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---
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---
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title: Double Buffer
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category: Behavioral
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language: en
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tag:
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- Performance
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- Game programming
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---
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---
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## Intent
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Double buffering is a term used to describe a device that has two buffers. The usage of multiple buffers increases the overall throughput of a device and helps prevents bottlenecks. This example shows using double buffer pattern on graphics. It is used to show one image or frame while a separate frame is being buffered to be shown next. This method makes animations and games look more realistic than the same done in a single buffer mode.
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Double buffering is a term used to describe a device that has two buffers. The usage of multiple
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buffers increases the overall throughput of a device and helps prevents bottlenecks. This example
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shows using double buffer pattern on graphics. It is used to show one image or frame while a separate
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frame is being buffered to be shown next. This method makes animations and games look more realistic
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than the same done in a single buffer mode.
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## Explanation
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Real world example
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> A typical example, and one that every game engine must address, is rendering. When the game draws
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> the world the users see, it does so one piece at a time -- the mountains in the distance,
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> the rolling hills, the trees, each in its turn. If the user watched the view draw incrementally
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> like that, the illusion of a coherent world would be shattered. The scene must update smoothly
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> and quickly, displaying a series of complete frames, each appearing instantly. Double buffering solves
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> the problem.
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In plain words
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> It ensures a state that is being rendered correctly while that state is modifying incrementally. It is
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> widely used in computer graphics.
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Wikipedia says
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> In computer science, multiple buffering is the use of more than one buffer to hold a block of data,
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> so that a "reader" will see a complete (though perhaps old) version of the data, rather than a
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> partially updated version of the data being created by a "writer". It is very commonly used for
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> computer display images.
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**Programmatic Example**
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Buffer interface that assures basic functionalities of a buffer.
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```java
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/**
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* Buffer interface.
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*/
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public interface Buffer {
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/**
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* Clear the pixel in (x, y).
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*
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* @param x X coordinate
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* @param y Y coordinate
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*/
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void clear(int x, int y);
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/**
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* Draw the pixel in (x, y).
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*
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* @param x X coordinate
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* @param y Y coordinate
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*/
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void draw(int x, int y);
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/**
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* Clear all the pixels.
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*/
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void clearAll();
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/**
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* Get all the pixels.
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*
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* @return pixel list
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*/
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Pixel[] getPixels();
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}
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```
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One of the implementation of Buffer interface.
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```java
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/**
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* FrameBuffer implementation class.
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*/
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public class FrameBuffer implements Buffer {
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public static final int WIDTH = 10;
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public static final int HEIGHT = 8;
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private final Pixel[] pixels = new Pixel[WIDTH * HEIGHT];
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public FrameBuffer() {
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clearAll();
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}
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@Override
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public void clear(int x, int y) {
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pixels[getIndex(x, y)] = Pixel.WHITE;
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}
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@Override
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public void draw(int x, int y) {
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pixels[getIndex(x, y)] = Pixel.BLACK;
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}
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@Override
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public void clearAll() {
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Arrays.fill(pixels, Pixel.WHITE);
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}
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@Override
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public Pixel[] getPixels() {
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return pixels;
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}
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private int getIndex(int x, int y) {
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return x + WIDTH * y;
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}
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}
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```
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```java
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/**
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* Pixel enum. Each pixel can be white (not drawn) or black (drawn).
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*/
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public enum Pixel {
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WHITE,
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BLACK;
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}
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```
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Scene represents the game scene where current buffer has already been rendered.
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```java
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/**
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* Scene class. Render the output frame.
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*/
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@Slf4j
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public class Scene {
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private final Buffer[] frameBuffers;
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private int current;
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private int next;
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/**
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* Constructor of Scene.
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*/
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public Scene() {
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frameBuffers = new FrameBuffer[2];
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frameBuffers[0] = new FrameBuffer();
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frameBuffers[1] = new FrameBuffer();
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current = 0;
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next = 1;
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}
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/**
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* Draw the next frame.
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*
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* @param coordinateList list of pixels of which the color should be black
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*/
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public void draw(List<? extends Pair<Integer, Integer>> coordinateList) {
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LOGGER.info("Start drawing next frame");
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LOGGER.info("Current buffer: " + current + " Next buffer: " + next);
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frameBuffers[next].clearAll();
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coordinateList.forEach(coordinate -> {
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var x = coordinate.getKey();
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var y = coordinate.getValue();
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frameBuffers[next].draw(x, y);
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});
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LOGGER.info("Swap current and next buffer");
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swap();
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LOGGER.info("Finish swapping");
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LOGGER.info("Current buffer: " + current + " Next buffer: " + next);
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}
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public Buffer getBuffer() {
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LOGGER.info("Get current buffer: " + current);
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return frameBuffers[current];
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}
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private void swap() {
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current = current ^ next;
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next = current ^ next;
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current = current ^ next;
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}
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}
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```
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```java
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public static void main(String[] args) {
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final var scene = new Scene();
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var drawPixels1 = List.of(
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new MutablePair<>(1, 1),
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new MutablePair<>(5, 6),
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new MutablePair<>(3, 2)
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);
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scene.draw(drawPixels1);
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var buffer1 = scene.getBuffer();
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printBlackPixelCoordinate(buffer1);
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var drawPixels2 = List.of(
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new MutablePair<>(3, 7),
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new MutablePair<>(6, 1)
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);
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scene.draw(drawPixels2);
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var buffer2 = scene.getBuffer();
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printBlackPixelCoordinate(buffer2);
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}
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private static void printBlackPixelCoordinate(Buffer buffer) {
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StringBuilder log = new StringBuilder("Black Pixels: ");
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var pixels = buffer.getPixels();
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for (var i = 0; i < pixels.length; ++i) {
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if (pixels[i] == Pixel.BLACK) {
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var y = i / FrameBuffer.WIDTH;
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var x = i % FrameBuffer.WIDTH;
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log.append(" (").append(x).append(", ").append(y).append(")");
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}
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}
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LOGGER.info(log.toString());
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}
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```
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The console output
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```text
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[main] INFO com.iluwatar.doublebuffer.Scene - Start drawing next frame
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[main] INFO com.iluwatar.doublebuffer.Scene - Current buffer: 0 Next buffer: 1
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[main] INFO com.iluwatar.doublebuffer.Scene - Swap current and next buffer
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[main] INFO com.iluwatar.doublebuffer.Scene - Finish swapping
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[main] INFO com.iluwatar.doublebuffer.Scene - Current buffer: 1 Next buffer: 0
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[main] INFO com.iluwatar.doublebuffer.Scene - Get current buffer: 1
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[main] INFO com.iluwatar.doublebuffer.App - Black Pixels: (1, 1) (3, 2) (5, 6)
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[main] INFO com.iluwatar.doublebuffer.Scene - Start drawing next frame
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[main] INFO com.iluwatar.doublebuffer.Scene - Current buffer: 1 Next buffer: 0
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[main] INFO com.iluwatar.doublebuffer.Scene - Swap current and next buffer
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[main] INFO com.iluwatar.doublebuffer.Scene - Finish swapping
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[main] INFO com.iluwatar.doublebuffer.Scene - Current buffer: 0 Next buffer: 1
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[main] INFO com.iluwatar.doublebuffer.Scene - Get current buffer: 0
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[main] INFO com.iluwatar.doublebuffer.App - Black Pixels: (6, 1) (3, 7)
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```
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## Class diagram
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