AndEngine之DEMO学习（十）PathModifierExample

这是一个路径修改器配合动画精灵的例子，我准备分两块来说明，一个是路径修改器的构成；一个是动画精灵的构成。最后达到的效果是一个小人在屏幕四周循环跑动。

路径修改器中定义内部类Path，用于记录路径上的各个点坐标，PathModifier根据坐标生成MoveModifier，完成每两点的移动，一系列的MoveModifier放入一个顺序容器就完成了物体的移动。这种移动是没有与动画集成的，但是每完成两个点的移动就回调IPathModifierListener监听中的onPathWaypointStarted方法，于是可以在其中判断动画经理播放的动画。

动画精灵AnimatedSprite是一种特殊的TiledSprite。TiledSprite将同一个纹理切分为多个方形的显示区域，通过设置索引确定应该显示哪个区域。AnimatedSprite中按照指定时间、指定顺序变换TiledSprite的索引，完成动画的功能。

好了两个重要的部件已经介绍清楚了，程序中合并了两个部件完成人物的行走，下面上程序：

package org.andengine.examples;

import org.andengine.engine.camera.Camera;
import org.andengine.engine.options.EngineOptions;
import org.andengine.engine.options.ScreenOrientation;
import org.andengine.engine.options.resolutionpolicy.RatioResolutionPolicy;
import org.andengine.entity.IEntity;
import org.andengine.entity.modifier.LoopEntityModifier;
import org.andengine.entity.modifier.PathModifier;
import org.andengine.entity.modifier.PathModifier.IPathModifierListener;
import org.andengine.entity.modifier.PathModifier.Path;
import org.andengine.entity.scene.Scene;
import org.andengine.entity.scene.background.RepeatingSpriteBackground;
import org.andengine.entity.sprite.AnimatedSprite;
import org.andengine.entity.util.FPSLogger;
import org.andengine.opengl.texture.atlas.bitmap.BitmapTextureAtlas;
import org.andengine.opengl.texture.atlas.bitmap.BitmapTextureAtlasTextureRegionFactory;
import org.andengine.opengl.texture.atlas.bitmap.source.AssetBitmapTextureAtlasSource;
import org.andengine.opengl.texture.region.TiledTextureRegion;
import org.andengine.ui.activity.SimpleBaseGameActivity;
import org.andengine.util.debug.Debug;
import org.andengine.util.modifier.ease.EaseSineInOut;

import android.widget.Toast;

public class PathModifierExample extends SimpleBaseGameActivity {

	private static final int CAMERA_WIDTH = 720;
	private static final int CAMERA_HEIGHT = 480;

	private RepeatingSpriteBackground mGrassBackground;

	private BitmapTextureAtlas mBitmapTextureAtlas;
	private TiledTextureRegion mPlayerTextureRegion;

	@Override
	public EngineOptions onCreateEngineOptions() {
		Toast.makeText(this, "You move my sprite right round, right round...", Toast.LENGTH_LONG).show();

		final Camera camera = new Camera(0, 0, CAMERA_WIDTH, CAMERA_HEIGHT);

		return new EngineOptions(true, ScreenOrientation.LANDSCAPE_FIXED, new RatioResolutionPolicy(CAMERA_WIDTH, CAMERA_HEIGHT), camera);
	}

	@Override
	public void onCreateResources() {
		BitmapTextureAtlasTextureRegionFactory.setAssetBasePath("gfx/");

		this.mGrassBackground = new RepeatingSpriteBackground(CAMERA_WIDTH, CAMERA_HEIGHT, this.getTextureManager(), AssetBitmapTextureAtlasSource.create(this.getAssets(), "gfx/background_grass.png"), this.getVertexBufferObjectManager());

		this.mBitmapTextureAtlas = new BitmapTextureAtlas(this.getTextureManager(), 128, 128);
		this.mPlayerTextureRegion = BitmapTextureAtlasTextureRegionFactory.createTiledFromAsset(this.mBitmapTextureAtlas, this, "player.png", 0, 0, 3, 4);
		this.mBitmapTextureAtlas.load();
	}

	@Override
	public Scene onCreateScene() {
		this.mEngine.registerUpdateHandler(new FPSLogger());

		final Scene scene = new Scene();
		scene.setBackground(this.mGrassBackground);

		/* Create the face and add it to the scene. */
		final AnimatedSprite player = new AnimatedSprite(10, 10, 48, 64, this.mPlayerTextureRegion, this.getVertexBufferObjectManager());

		final Path path = new Path(5).to(10, 10).to(10, CAMERA_HEIGHT - 74).to(CAMERA_WIDTH - 58, CAMERA_HEIGHT - 74).to(CAMERA_WIDTH - 58, 10).to(10, 10);

		/* Add the proper animation when a waypoint of the path is passed. */
		player.registerEntityModifier(new LoopEntityModifier(new PathModifier(30, path, null, new IPathModifierListener() {
			@Override
			public void onPathStarted(final PathModifier pPathModifier, final IEntity pEntity) {
				Debug.d("onPathStarted");
			}

			//当Path中两点移动开始时调用，其中pWaypointIndex表示Path中的第几段
			@Override
			public void onPathWaypointStarted(final PathModifier pPathModifier, final IEntity pEntity, final int pWaypointIndex) {
				Debug.d("onPathWaypointStarted:  " + pWaypointIndex);
				switch(pWaypointIndex) {
					case 0:
						player.animate(new long[]{200, 200, 200}, 6, 8, true);
						break;
					case 1:
						player.animate(new long[]{200, 200, 200}, 3, 5, true);
						break;
					case 2:
						player.animate(new long[]{200, 200, 200}, 0, 2, true);
						break;
					case 3:
						player.animate(new long[]{200, 200, 200}, 9, 11, true);
						break;
				}
			}

			@Override
			public void onPathWaypointFinished(final PathModifier pPathModifier, final IEntity pEntity, final int pWaypointIndex) {
				Debug.d("onPathWaypointFinished: " + pWaypointIndex);
			}

			@Override
			public void onPathFinished(final PathModifier pPathModifier, final IEntity pEntity) {
				Debug.d("onPathFinished");
			}
		}, EaseSineInOut.getInstance())));
		scene.attachChild(player);

		return scene;
	}
}

应该来说这个例子中动画的切换并没有真正的实现，实际应该通过对路径中两点的坐标差完成动画的选择，应该的写demo的家伙在偷懒吧。有了这个思想，完全可以实现人物的八方向或者十六方向行走，只需要在适当的时候切换动画就可以了。

这里又想多罗嗦两句，之前一直觉得人物的移动是个很麻烦的事情，也想了一些办法来实现，看了AndEngine的实现发现哪些想法真是丑陋无比啊，在事物的抽象方面他确实下了很大的功夫，不经意间问题迎刃而解，单不看Engine的一些细节，面向对象的思想就值得好好去学习一下。