Android 2d物理引擎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：
?
?
?
?
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/
1 楼 诸葛紧 2009-08-04 这里有人移植box2d