Android 2d物理发动机Box2d的使用示例

Box2d是一个很出名的2d物理引擎，大家可以google之。Box2d有C++，flash和Java等版本。android可以直接使用java版本的Jbox2d，但因为Jbox2d的图形渲染是使用processing库来实现的，所以，在android中使用Jbox2d的时候，图形渲染的工作就只能自己来写了。因为网上关于box2d的资料真的非常的少，特别是关于图形绘制方面，所以，虽然程序写得不是很好，还是贴上来了，先看截图：

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程序很简单：蓝色的是地面，从上面掉下两个绿球和一个红色的方块，它们之间的碰撞都由box2d引擎自己来完成。

（这程序运行起来有点卡，我 也正在解决这个问题，有朋友知道答案的也请分享一下啦！）

代码如下：

package com.ray.test;import org.jbox2d.collision.AABB;import org.jbox2d.collision.CircleDef;import org.jbox2d.collision.PolygonDef;import org.jbox2d.common.Vec2;import org.jbox2d.dynamics.Body;import org.jbox2d.dynamics.BodyDef;import org.jbox2d.dynamics.World;import android.app.Activity;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.os.Bundle;import android.os.Handler;import android.view.View;import android.view.Window;import android.view.WindowManager;public class MyBox2d extends Activity {		private final static int RATE = 10;//屏幕到现实世界的比例 10px：1m;	private AABB worldAABB;//创建 一个管理碰撞的世界	private World world;	private float timeStep = 1/60;//模拟的的频率	private int iterations = 10;//迭代越大，模拟约精确，但性能越低	private Body body,body2,body3;	private MyView myView;	private Handler mHandler;    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        requestWindowFeature(Window.FEATURE_NO_TITLE);        getWindow().setFlags(WindowManager.LayoutParams. FLAG_FULLSCREEN ,        WindowManager.LayoutParams. FLAG_FULLSCREEN);                worldAABB = new AABB();                //上下界，以屏幕的左上方为 原点，如果创建的刚体到达屏幕的边缘的话，会停止模拟        worldAABB.lowerBound.set(-100.0f,-100.0f)；        worldAABB.upperBound.set(100.0f, 100.0f);//注意这里使用的是现实世界的单位                Vec2 gravity = new Vec2(0.0f,10.0f);        boolean doSleep = true;                world = new World(worldAABB, gravity, doSleep);//创建世界                createBox(160, 470, 160, 10, true);             createBox1(160, 150, 160, 10, false);                createCircle(160, 100, 10);        createCircle1(150, 60, 10);        timeStep = 1.0f/60.0f;        iterations = 10;                myView = new MyView(this);        setContentView(myView);        mHandler = new Handler();        mHandler.post(update);    }        private Runnable update = new Runnable() {        public void run() {            	world.step(timeStep, iterations);//开始模拟            	Vec2 position = body.getPosition();            	Vec2 position1 = body2.getPosition();            	Vec2 position2 = body3.getPosition();            	myView.x=position.x*RATE;            	myView.y=position.y*RATE;            	            	myView.x1=position1.x*RATE;             	myView.y1=position1.y*RATE;            	            	myView.x2=position2.x*RATE;            	myView.y2=position2.y*RATE;                myView.update();                mHandler.postDelayed(update, (long)timeStep*1000);        }    };        public void createBox(float x,float y,float half_width,float half_height,                     boolean isStatic){     	PolygonDef shape = new PolygonDef();    	if(isStatic){shape.density = 0;}    	else{shape.density = 2.0f;}    	shape.friction = 0.8f;    	shape.restitution = 0.3f;    	shape.setAsBox(half_width/RATE, half_height/RATE);    	    	BodyDef bodyDef = new BodyDef();    	bodyDef.position.set(x/RATE, y/RATE);    	Body body1= world.createBody(bodyDef);    	body1.createShape(shape);    	body1.setMassFromShapes();    }        public void createCircle(float x,float y,float radius){    	CircleDef shape = new CircleDef();    	shape.density = 7;    	shape.friction = 0.2f;    	shape.radius = radius/RATE;    	    	BodyDef bodyDef = new BodyDef();    	bodyDef.position.set(x/RATE, y/RATE);    	body2 = world.createBody(bodyDef);    	body2.createShape(shape);    	body2.setMassFromShapes();    }        public void createCircle1(float x,float y,float radius){    	CircleDef shape = new CircleDef();    	shape.density = 7;    	shape.friction = 0.2f;    	shape.radius = radius/RATE;    	    	BodyDef bodyDef = new BodyDef();    	bodyDef.position.set(x/RATE, y/RATE);    	body3 = world.createBody(bodyDef);    	body3.createShape(shape);    	body3.setMassFromShapes();    }        public void createBox1(float x,float y,float half_width,float half_height,                   boolean isStatic){     	PolygonDef shape = new PolygonDef();    	if(isStatic){shape.density = 0;}    	else{shape.density = 2.0f;}    	shape.friction = 0.3f;    	shape.setAsBox(half_width/RATE, half_height/RATE);    	    	BodyDef bodyDef = new BodyDef();    	bodyDef.position.set(x/RATE, y/RATE);    	body= world.createBody(bodyDef);    	body.createShape(shape);    	body.setMassFromShapes();    }        class MyView extends View{    	Canvas canvas;    	public float x=160,y=150;    	public float x1=160,y1=100;    	public float x2=150,y2=60;		public MyView(Context context) {			super(context);		}		public void drawBox(float x,float y){			Paint mPaint = new Paint();			mPaint.setAntiAlias(true);			mPaint.setColor(Color.RED);			canvas.drawRect(x-160, y-10, x+160, y+10, mPaint);		}				public void drawGround(){			Paint mPaint = new Paint();			mPaint.setAntiAlias(true);			mPaint.setColor(Color.BLUE);			canvas.drawRect(0, 460, 320, 480, mPaint);		}				public void drawCircle(float x1,float y1){			Paint mPaint = new Paint();			mPaint.setAntiAlias(true);			mPaint.setColor(Color.GREEN);			canvas.drawCircle(x1, y1, 10, mPaint);		}				public void update(){			postInvalidate();		}				protected void onDraw(Canvas canvas) {			super.onDraw(canvas);			this.canvas = canvas;			drawGround();			drawBox(x, y);			drawCircle(x1, y1);			drawCircle(x2, y2);		}		    	    }}

?程序运行的时候需要加载Jbox2d的库，可到以下地址下载（使用的是不带渲染部分的库jbox2d-2.0.1-library-only.jar）：

http://sourceforge.net/projects/jbox2d/