package com.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;//屏幕到現實世界的比例 10px：1m; private AABB worldAABB; //創建 一個管理碰撞的世界 private World world; private float timeStep = 1/60;//模擬的的頻率 private int iterations = 10;//迭代越大，模擬約精確，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，以屏幕的左上方為 原點，如果創建的剛體到達屏幕的邊緣的話，會停止模擬    worldAABB.lowerBound.set(-100.0f,-100.0f)；    worldAABB.upperBound.set(100.0f, 100.0f);    //注意這里使用的是現實世界的單位    Vec2 gravity = new Vec2(0.0f,10.0f);    boolean doSleep = true;    world = new World(worldAABB, gravity, doSleep);//創建世界    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);//開始模擬       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); } }}