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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);   }       } }