andengine编程之background（一）

这次，我们来谈谈背景background的一些类及用法。关于background的用法，AndEngineExamples中有单独的例子分别介绍了，在这里，我们也只是将例子稍加改造。

AndEngineExamples中第一个例子便是AutoParallaxBackgroundExample——自动视差背景。也就是有层次感的背影移动变化。比如人在场景中跑动，我们为了衬托出人物是在跑动，就会例如增加几朵云，让它向人物跑动的方向移动，这样人们就会认为人物是跑起来的。但实际上，人物并没有移动位置。

早期，做过横版过关游戏的人都要自己去实现视差背景，大致上讲，就是让人物坐标基本不动，让背景也保持不动，让中间一层（街道，地面）向人物相反方向移动。如果想做得更精细些，就会增加一些云彩，但云彩又不能和地面移动的速度一样，就需要单独设置云彩的移动速度。

好了，andengine已经为我设计好了这些接下来看看它是怎么做的。

AutoParallaxBackground——自动视差背景类，我们所有操作都要基于它的对象来实现。
AutoParallaxBackground只有一个构造方法：
public AutoParallaxBackground(final float pRed, final float pGreen, final float pBlue, final float pParallaxChangePerSecond) ：
前三个很简单，分别对应的颜色数值；pParallaxChangePerSecond为背景每秒移动的距离。

让我很不解的是：以AutoParallaxBackground作者的风格，会封装很多适合大家所需的方法。背景颜色一般没人会去设置，所以，这里其实还应该再增加一个构造方法：

	public AutoParallaxBackground(final float pParallaxChangePerSecond) {
		super(0, 0, 0);
		this.mParallaxChangePerSecond = pParallaxChangePerSecond;
	}

public void attachParallaxEntity(final ParallaxEntity pParallaxEntity)，这个方法来自于其父类，需要传入一个ParallaxEntity的对象。
从ParallaxEntity的构造方法来看：
public ParallaxEntity(final float pParallaxFactor, final IAreaShape pAreaShape) ：pParallaxFactor背景移动的相对数值。pAreaShape一般为精灵对象。

public void setParallaxValue(final float pParallaxValue)：设置背景的初始位置。你可以理解成X轴的位置。

public void setParallaxChangePerSecond(final float pParallaxChangePerSecond)：设置每秒移动的距离，这个和构造方法中的最后一个参数是一样的。我们主要就是通过改变这个值来实现背景的移动。

这里直接用AutoParallaxBackgroundExample的例子，并稍加改造：

	public void onCreateScene(OnCreateSceneCallback pOnCreateSceneCallback)
			throws Exception {
		Scene mScene = new Scene();

		// 最后一个参数原来是5，我们这里设为0，意思是让它一开始不要滚动
		final AutoParallaxBackground autoParallaxBackground = new AutoParallaxBackground(
				0, 0, 0, 0);

		// 0.0f，-0.5f，-10.0f：你可以把它们理解为相对位置差
		autoParallaxBackground
				.attachParallaxEntity(new ParallaxEntity(0.0f,
						new Sprite(0, CAMERA_HEIGHT
								- this.mParallaxLayerBack.getHeight(),
								this.mParallaxLayerBack,
								getVertexBufferObjectManager())));
		autoParallaxBackground.attachParallaxEntity(new ParallaxEntity(-5.0f,
				new Sprite(0, 80, this.mParallaxLayerMid,
						getVertexBufferObjectManager())));
		autoParallaxBackground.attachParallaxEntity(new ParallaxEntity(-10.0f,
				new Sprite(0, CAMERA_HEIGHT
						- this.mParallaxLayerFront.getHeight(),
						this.mParallaxLayerFront,
						getVertexBufferObjectManager())));

		// 设置背景
		mScene.setBackground(autoParallaxBackground);

		final int playerX = (int) (CAMERA_WIDTH - this.mPlayerTextureRegion
				.getWidth()) / 2;
		final int playerY = (int) (CAMERA_HEIGHT
				- this.mPlayerTextureRegion.getHeight() - 5);
		final AnimatedSprite player = new AnimatedSprite(playerX, playerY,
				this.mPlayerTextureRegion, getVertexBufferObjectManager());
		player.setScaleCenterY(this.mPlayerTextureRegion.getHeight());
		player.setScale(2);
		player.animate(new long[] { 200, 200, 200 }, 3, 5, true);

		mScene.attachChild(player);

		// 我们新增加一个触摸事件监听
		mScene.setOnSceneTouchListener(new IOnSceneTouchListener() {
			public boolean onSceneTouchEvent(Scene pScene,
					TouchEvent pSceneTouchEvent) {
				switch (pSceneTouchEvent.getAction()) {
				case TouchEvent.ACTION_UP:// 当触屏抬起的时候
					// 如果在右边触摸，我们让屏幕向左滚动
					if (pSceneTouchEvent.getX() > 400) {
						// 设置每秒钟背景滚动的距离
						autoParallaxBackground.setParallaxChangePerSecond(10);
						// 设置一下小人的帧序列
						player.animate(new long[] { 200, 200, 200 }, 3, 5, true);
					}
					// 如果在左边触摸，我们让屏幕向右滚动
					else {
						// 设置每秒钟背景滚动的距离
						autoParallaxBackground.setParallaxChangePerSecond(-10);
						// 设置一下小人的帧序列
						player.animate(new long[] { 200, 200, 200 }, 9, 11,
								true);
					}
					break;
				}
				return true;
			}
		});
		pOnCreateSceneCallback.onCreateSceneFinished(mScene);
	}

好了，你看明白了吗，以下是源代码：

package com.testsprite;

import org.andengine.engine.camera.Camera;
import org.andengine.engine.options.EngineOptions;
import org.andengine.engine.options.EngineOptions.ScreenOrientation;
import org.andengine.engine.options.resolutionpolicy.FillResolutionPolicy;
import org.andengine.entity.modifier.LoopEntityModifier;
import org.andengine.entity.scene.IOnSceneTouchListener;
import org.andengine.entity.scene.Scene;
import org.andengine.entity.scene.background.AutoParallaxBackground;
import org.andengine.entity.scene.background.ParallaxBackground.ParallaxEntity;
import org.andengine.entity.sprite.AnimatedSprite;
import org.andengine.entity.sprite.Sprite;
import org.andengine.input.touch.TouchEvent;
import org.andengine.opengl.texture.TextureOptions;
import org.andengine.opengl.texture.atlas.bitmap.BitmapTextureAtlas;
import org.andengine.opengl.texture.atlas.bitmap.BitmapTextureAtlasTextureRegionFactory;
import org.andengine.opengl.texture.region.TextureRegion;
import org.andengine.opengl.texture.region.TiledTextureRegion;
import org.andengine.ui.activity.BaseGameActivity;

public class TestSprite extends BaseGameActivity {
	private static final int CAMERA_WIDTH = 720;
	private static final int CAMERA_HEIGHT = 480;

	private BitmapTextureAtlas mBitmapTextureAtlas;
	private TiledTextureRegion mPlayerTextureRegion;

	private BitmapTextureAtlas mAutoParallaxBackgroundTexture;

	private TextureRegion mParallaxLayerBack;
	private TextureRegion mParallaxLayerMid;
	private TextureRegion mParallaxLayerFront;

	public EngineOptions onCreateEngineOptions() {
		Camera mCamera = new Camera(0, 0, CAMERA_WIDTH, CAMERA_HEIGHT);
		EngineOptions mEngineOptions = new EngineOptions(true,
				ScreenOrientation.LANDSCAPE_FIXED, new FillResolutionPolicy(),
				mCamera);
		return mEngineOptions;
	}

	public void onCreateResources(
			OnCreateResourcesCallback pOnCreateResourcesCallback)
			throws Exception {
		this.mBitmapTextureAtlas = new BitmapTextureAtlas(getTextureManager(),
				128, 128, TextureOptions.BILINEAR_PREMULTIPLYALPHA);
		this.mPlayerTextureRegion = BitmapTextureAtlasTextureRegionFactory
				.createTiledFromAsset(this.mBitmapTextureAtlas, this,
						"player.png", 0, 0, 3, 4);

		this.mAutoParallaxBackgroundTexture = new BitmapTextureAtlas(
				getTextureManager(), 1024, 1024, TextureOptions.DEFAULT);
		this.mParallaxLayerFront = (TextureRegion) BitmapTextureAtlasTextureRegionFactory
				.createFromAsset(this.mAutoParallaxBackgroundTexture, this,
						"parallax_background_layer_front.png", 0, 0);
		this.mParallaxLayerBack = (TextureRegion) BitmapTextureAtlasTextureRegionFactory
				.createFromAsset(this.mAutoParallaxBackgroundTexture, this,
						"parallax_background_layer_back.png", 0, 188);
		this.mParallaxLayerMid = (TextureRegion) BitmapTextureAtlasTextureRegionFactory
				.createFromAsset(this.mAutoParallaxBackgroundTexture, this,
						"parallax_background_layer_mid.png", 0, 669);

		mBitmapTextureAtlas.load();
		mAutoParallaxBackgroundTexture.load();

		pOnCreateResourcesCallback.onCreateResourcesFinished();
	}

	LoopEntityModifier mLoopEntityModifier;

	public void onCreateScene(OnCreateSceneCallback pOnCreateSceneCallback)
			throws Exception {
		Scene mScene = new Scene();

		// 最后一个参数原来是5，我们这里设为0，意思是让它一开始不要滚动
		final AutoParallaxBackground autoParallaxBackground = new AutoParallaxBackground(
				0, 0, 0, 0);

		// 0.0f，-0.5f，-10.0f：你可以把它们理解为相对位置差
		autoParallaxBackground
				.attachParallaxEntity(new ParallaxEntity(0.0f,
						new Sprite(0, CAMERA_HEIGHT
								- this.mParallaxLayerBack.getHeight(),
								this.mParallaxLayerBack,
								getVertexBufferObjectManager())));
		autoParallaxBackground.attachParallaxEntity(new ParallaxEntity(-5.0f,
				new Sprite(0, 80, this.mParallaxLayerMid,
						getVertexBufferObjectManager())));
		autoParallaxBackground.attachParallaxEntity(new ParallaxEntity(-10.0f,
				new Sprite(0, CAMERA_HEIGHT
						- this.mParallaxLayerFront.getHeight(),
						this.mParallaxLayerFront,
						getVertexBufferObjectManager())));

		// 设置背景
		mScene.setBackground(autoParallaxBackground);

		final int playerX = (int) (CAMERA_WIDTH - this.mPlayerTextureRegion
				.getWidth()) / 2;
		final int playerY = (int) (CAMERA_HEIGHT
				- this.mPlayerTextureRegion.getHeight() - 5);
		final AnimatedSprite player = new AnimatedSprite(playerX, playerY,
				this.mPlayerTextureRegion, getVertexBufferObjectManager());
		player.setScaleCenterY(this.mPlayerTextureRegion.getHeight());
		player.setScale(2);
		player.animate(new long[] { 200, 200, 200 }, 3, 5, true);

		mScene.attachChild(player);

		// 我们新增加一个触摸事件监听
		mScene.setOnSceneTouchListener(new IOnSceneTouchListener() {
			public boolean onSceneTouchEvent(Scene pScene,
					TouchEvent pSceneTouchEvent) {
				switch (pSceneTouchEvent.getAction()) {
				case TouchEvent.ACTION_UP:// 当触屏抬起的时候
					// 如果在右边触摸，我们让屏幕向左滚动
					if (pSceneTouchEvent.getX() > 400) {
						// 设置每秒钟背景滚动的距离
						autoParallaxBackground.setParallaxChangePerSecond(10);
						// 设置一下小人的帧序列
						player.animate(new long[] { 200, 200, 200 }, 3, 5, true);
					}
					// 如果在左边触摸，我们让屏幕向右滚动
					else {
						// 设置每秒钟背景滚动的距离
						autoParallaxBackground.setParallaxChangePerSecond(-10);
						// 设置一下小人的帧序列
						player.animate(new long[] { 200, 200, 200 }, 9, 11,
								true);
					}
					break;
				}
				return true;
			}
		});
		pOnCreateSceneCallback.onCreateSceneFinished(mScene);
	}

	public void onPopulateScene(Scene pScene,
			OnPopulateSceneCallback pOnPopulateSceneCallback) throws Exception {
		pOnPopulateSceneCallback.onPopulateSceneFinished();
	}
}

自动视差背景