Andengine的自動視差背景AutoParallaxBackground（背景移動）

（轉自：http://blog.csdn.net/xyz_fly/article/details/7466643）

這次，我們來談談背景background的一些類及用法。關於background的用法，AndEngineExamples中有單獨的例子分別介紹了，在這裏，我們也只是將例子稍加改造。

AndEngineExamples中第一個例子便是AutoParallaxBackgroundExample——自動視差背景。也就是有層次感的背影移動變化。比如人在場景中跑動，我們爲了襯托出人物是在跑動，就會例如增加幾朵雲，讓它向人物跑動的方向移動，這樣人們就會認爲人物是跑起來的。但實際上，人物並沒有移動位置。

早期，做過橫版過關遊戲的人都要自己去實現視差背景，大致上講，就是讓人物座標基本不動，讓背景也保持不動，讓中間一層（街道，地面）向人物相反方向移動。如果想做得更精細些，就會增加一些雲彩，但云彩又不能和地面移動的速度一樣，就需要單獨設置雲彩的移動速度。

好了，andengine已經爲我設計好了這些接下來看看它是怎麼做的。

AutoParallaxBackground——自動視差背景類，我們所有操作都要基於它的對象來實現。
AutoParallaxBackground只有一個構造方法：
public AutoParallaxBackground(final float pRed, final float pGreen, final float pBlue, final float pParallaxChangePerSecond) ：
前三個很簡單，分別對應的顏色數值；pParallaxChangePerSecond爲背景每秒移動的距離。

讓我很不解的是：以AutoParallaxBackground作者的風格，會封裝很多適合大家所需的方法。背景顏色一般沒人會去設置，所以，這裏其實還應該再增加一個構造方法：

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

public void attachParallaxEntity(final ParallaxEntity pParallaxEntity)，這個方法來自於其父類，需要傳入一個ParallaxEntity的對象。
從ParallaxEntity的構造方法來看：
public ParallaxEntity(final float pParallaxFactor, final IAreaShape pAreaShape) ：pParallaxFactor背景移動的相對數值。pAreaShape一般爲精靈對象。

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

public void setParallaxChangePerSecond(final float pParallaxChangePerSecond)：設置每秒移動的距離，這個和構造方法中的最後一個參數是一樣的。我們主要就是通過改變這個值來實現背景的移動。

這裏直接用AutoParallaxBackgroundExample的例子，並稍加改造：

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

    // 最後一個參數原來是5，我們這裏設爲0，意思是讓它一開始不要滾動
    final AutoParallaxBackground autoParallaxBackground = new AutoParallaxBackground(
            0, 0, 0, 0);

    // 0.0f，-0.5f，-10.0f：你可以把它們理解爲相對位置差
    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())));

    // 設置背景
    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);

    // 我們新增加一個觸摸事件監聽
    mScene.setOnSceneTouchListener(new IOnSceneTouchListener() {
        public boolean onSceneTouchEvent(Scene pScene,
                TouchEvent pSceneTouchEvent) {
            switch (pSceneTouchEvent.getAction()) {
            case TouchEvent.ACTION_UP:// 當觸屏擡起的時候
                // 如果在右邊觸摸，我們讓屏幕向左滾動
                if (pSceneTouchEvent.getX() > 400) {
                    // 設置每秒鐘背景滾動的距離
                    autoParallaxBackground.setParallaxChangePerSecond(10);
                    // 設置一下小人的幀序列
                    player.animate(new long[] { 200, 200, 200 }, 3, 5, true);
                }
                // 如果在左邊觸摸，我們讓屏幕向右滾動
                else {
                    // 設置每秒鐘背景滾動的距離
                    autoParallaxBackground.setParallaxChangePerSecond(-10);
                    // 設置一下小人的幀序列
                    player.animate(new long[] { 200, 200, 200 }, 9, 11,
                            true);
                }
                break;
            }
            return true;
        }
    });
    pOnCreateSceneCallback.onCreateSceneFinished(mScene);
}

好了，你看明白了嗎，以下是源代碼：

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();

        // 最後一個參數原來是5，我們這裏設爲0，意思是讓它一開始不要滾動
        final AutoParallaxBackground autoParallaxBackground = new AutoParallaxBackground(
                0, 0, 0, 0);

        // 0.0f，-0.5f，-10.0f：你可以把它們理解爲相對位置差
        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())));

        // 設置背景
        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);

        // 我們新增加一個觸摸事件監聽
        mScene.setOnSceneTouchListener(new IOnSceneTouchListener() {
            public boolean onSceneTouchEvent(Scene pScene,
                    TouchEvent pSceneTouchEvent) {
                switch (pSceneTouchEvent.getAction()) {
                case TouchEvent.ACTION_UP:// 當觸屏擡起的時候
                    // 如果在右邊觸摸，我們讓屏幕向左滾動
                    if (pSceneTouchEvent.getX() > 400) {
                        // 設置每秒鐘背景滾動的距離
                        autoParallaxBackground.setParallaxChangePerSecond(10);
                        // 設置一下小人的幀序列
                        player.animate(new long[] { 200, 200, 200 }, 3, 5, true);
                    }
                    // 如果在左邊觸摸，我們讓屏幕向右滾動
                    else {
                        // 設置每秒鐘背景滾動的距離
                        autoParallaxBackground.setParallaxChangePerSecond(-10);
                        // 設置一下小人的幀序列
                        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();
    }
}

自動視差背景