#define PIXEL_TO_METER 30

    #include "Box2D/Box2D.h"

    void createWorld();  //创建物理世界

    void createWall();   //创建四周墙体

    void createBall();   //创建刚体

b2World* world;
    b2Body* wallBody ;

float32 wallLineOffset ;

void HelloWorld::createWorld()

{

    b2Vec2 gravity;

    gravity.Set(0.0f,-9.0f);   //物理世界重力向量，这里创建一个向下的重力向量

    b2BodyDef* bodydef = new b2BodyDef();

    world = new b2World(gravity);    //根据重力向量创建物理世界对象

    world->SetAllowSleeping(true);   //允许休眠

    world->SetWarmStarting(true);    //初始状态将受到重力影响

}

void HelloWorld::createWall(){

    CCSize s = CCDirector::sharedDirector()->getVisibleSize();

    b2BodyDef wallDef ;   //刚体定义

    wallDef.position.Set(0,0);  //位置

    wallBody = world->CreateBody(&wallDef);   //创建一个刚体（四周墙体）

    b2EdgeShape wallShape;   //形状

    //下   wallLineOffset 方便调整显示位置

    wallShape.Set(b2Vec2(0,0+wallLineOffset), b2Vec2(s.width/PIXEL_TO_METER,0+wallLineOffset));  //设置形状大小

    wallBody->CreateFixture(&wallShape,0);   //将形状连接到框架上

    //上

    wallShape.Set(b2Vec2(0,s.height/PIXEL_TO_METER-wallLineOffset),b2Vec2(s.width/PIXEL_TO_METER,s.height/PIXEL_TO_METER-wallLineOffset));

    wallBody->CreateFixture(&wallShape,0);

    //左

    wallShape.Set(b2Vec2(0+wallLineOffset,s.height/PIXEL_TO_METER),b2Vec2(0+wallLineOffset,0));

    wallBody->CreateFixture(&wallShape,0);

    //右

    wallShape.Set(b2Vec2(s.width/PIXEL_TO_METER-wallLineOffset,s.height/PIXEL_TO_METER),b2Vec2(s.width/PIXEL_TO_METER-wallLineOffset,0));

    wallBody->CreateFixture(&wallShape,0);

}

void HelloWorld::createBall(){

    CCSize s = CCDirector::sharedDirector()->getVisibleSize();

    for(int i= 0; i < 5; i++)

    {

        b2BodyDef ballDef ;

        ballDef.type = b2_dynamicBody;  //设置刚体为动态物体

        b2CircleShape circleShape ;    //刚体碰撞使用的形状

        b2FixtureDef ballFixtureDef ;

        circleShape.m_p.Set(1.0+i,5.0);

        circleShape.m_radius= 0.5f;

        //刚体连接的框架设置

        ballFixtureDef.shape = &circleShape;

        ballFixtureDef.density = 1.0;

        ballFixtureDef.restitution = 0.8;    //设置重力恢复系数

        ballFixtureDef.friction = 0.3f;

        ballDef.position.Set(s.width/2/PIXEL_TO_METER,20/PIXEL_TO_METER);

        b2Body* ball = world->CreateBody(&ballDef); //根据刚体定义创建刚体

        ball->CreateFixture(&ballFixtureDef);       //关联框架到刚体上

    }

}

wallLineOffset = 0.5;

    this->createWorld();

    this->createWall();

    this->createBall();