物理引擎：用来模拟一套物理事件的物理代码。

#ifndef __HELLOWORLD_SCENE_H__

#define __HELLOWORLD_SCENE_H__

#include "cocos2d.h"

#include <Box2D/Box2D.h>

#define RATIO 80.0f

class HelloWorld : public cocos2d::Layer,public b2ContactListener

{

private:

b2World *world;

b2Body *groundBody;

public:

static cocos2d::Scene* createScene();

virtual bool init();

void menuCloseCallback(cocos2d::Ref* pSender);

virtual void update(float dt);

virtual void BeginContact(b2Contact* contact);

void addRect(float x,float y,b2BodyType type);

void addGround();

CREATE_FUNC(HelloWorld);

};

#endif // __HELLOWORLD_SCENE_H__

#include "HelloWorldScene.h"

USING_NS_CC;

Scene* HelloWorld::createScene()

{

auto scene = Scene::create();

auto layer = HelloWorld::create();

scene->addChild(layer);

return scene;

}

bool HelloWorld::init()

{

if ( !Layer::init() )

{

return false;

}

Size visibleSize = Director::getInstance()->getVisibleSize();

Vec2 origin = Director::getInstance()->getVisibleOrigin();

//创建世界

world=new b2World(b2Vec2(0,-10));

world->SetContactListener(this);

addGround();

addRect(5,5,b2_dynamicBody);

//addRect(1,5,b2_kinematicBody);//漂浮物体，不受重力影响

scheduleUpdate();

return true;

}

void HelloWorld::update(float dt){

world->Step(dt,8,3);

Sprite *s;

for (b2Body *b=world->GetBodyList();b;b=b->GetNext()) {

//if (b->GetType()==b2_dynamicBody) {

//log("%f",b->GetPosition().y);

if (b->GetUserData()) {

s=(Sprite*)b->GetUserData();

s->setPosition(b->GetPosition().x*RATIO,b->GetPosition().y*RATIO);

}

//}

}

}

void HelloWorld::BeginContact(b2Contact *contact){

if (contact->GetFixtureA()->GetBody()==groundBody||contact->GetFixtureB()->GetBody()==groundBody) {

log("有物体落在了地板上");

}

}

void HelloWorld::addRect(float positionX,float positionY,b2BodyType type){

//config box2d

b2BodyDef def;

def.position=b2Vec2(positionX,positionY);

//def.linearVelocity=b2Vec2(1,0);

//def.linearVelocity=b2Vec2(0,10);

def.type=type;

groundBody=world->CreateBody(&def);

b2PolygonShape shape;

shape.SetAsBox(0.5,0.5);

b2FixtureDef fixtureDef;

fixtureDef.density=1;

fixtureDef.friction=0.3;

fixtureDef.shape=&shape;

groundBody->CreateFixture(&fixtureDef);

//config cocos shape

auto s=Sprite::create();

s->setTextureRect(Rect(0,0,0.5*2*RATIO,0.5*2*RATIO));

addChild(s);

//s->setPosition(Point(def.position.x*RATIO,def.position.y*RATIO));

groundBody->SetUserData(s);

}

void HelloWorld::addGround(){

b2BodyDef def;

def.position=b2Vec2(400/RATIO,0);

def.type=b2_staticBody;

b2Body *body=world->CreateBody(&def);

b2PolygonShape groundShape;

groundShape.SetAsBox(400/RATIO,0.5);

b2FixtureDef fixureDef;

fixureDef.density=1;

fixureDef.friction=0.3;

fixureDef.shape=&groundShape;

body->CreateFixture(&fixureDef);

}

void HelloWorld::menuCloseCallback(Ref* pSender)

{

Director::getInstance()->end();

#if (CC_TARGET_PLATFORM == CC_PLATFORM_IOS)

exit(0);

#endif

}