Android 2d物理引擎Box2d介绍

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);
  }
  
     
    }
}

 

 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/

Box2d NDK
http://download.csdn.net/down/2655805/laschweinski