Android下2d物理引擎Box2d用法简单实例

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);
 }
 }
}