Android 2d實體引擎Box2d介紹

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;//螢幕到現實世界的比例 10px：1m;

 private AABB worldAABB;

//建立 一個管理碰撞的世界

 private World world;

 private float timeStep = 1/60;//模拟的的頻率

 private int iterations = 10;//疊代越大，模拟約精确，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，以螢幕的左上方為 原點，如果建立的剛體到達螢幕的邊緣的話，會停止模拟

        worldAABB.lowerBound.set(-100.0f,-100.0f)；

        worldAABB.upperBound.set(100.0f, 100.0f);//注意這裡使用的是現實世界的機關

        Vec2 gravity = new Vec2(0.0f,10.0f);

        boolean doSleep = true;

        world = new World(worldAABB, gravity, doSleep);//建立世界

        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);

  }

    }

}

 程式運作的時候需要加載Jbox2d的庫，可到以下位址下載下傳（使用的是不帶渲染部分的庫jbox2d-2.0.1-library-only.jar）：

http://sourceforge.net/projects/jbox2d/

Box2d NDK

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