实例介绍Cocos2d-x中Box2D物理引擎：HelloBox2D

我们通过一个实例介绍一下，在Cocos2d-x 3.x中使用Box2D物理引擎的开发过程，熟悉这些API的使用。这个实例运行后的场景如图所示，当场景启动后，玩家可以触摸点击屏幕，每次触摸时候，就会在触摸点生成一个新的精灵，精灵的运行自由落体运动。
  

#ifndef __HELLOWORLD_SCENE_H__
#define __HELLOWORLD_SCENE_H__


#include "cocos2d.h"
#include "Box2D/Box2D.h"												①


#define PTM_RATIO 32													②


class HelloWorld : public cocos2d::Layer
{
	b2World* world;														③


public:
    static cocos2d::Scene* createScene();
    virtual bool init();  


	virtual void update(float dt);												④
	virtual bool onTouchBegan(cocos2d::Touch* touch, cocos2d::Event* event); 			⑤


    CREATE_FUNC(HelloWorld);
	
	void initPhysics();														⑥
	void addNewSpriteAtPosition(cocos2d::Vec2 p);								⑦


};


#endif // __HELLOWORLD_SCENE_H__

bool HelloWorld::init()
{
	if ( !Layer::init() )
	{
		return false;
	}


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


	// 初始化物理引擎
	this->initPhysics();													①


	setTouchEnabled(true);												
	//设置为单点触摸
	setTouchMode(Touch::DispatchMode::ONE_BY_ONE);							
	//开始游戏循环
	scheduleUpdate();													②


	return true;
}

void HelloWorld::initPhysics()
{
	Size s = Director::getInstance()->getVisibleSize();
	
	//重力参数
	b2Vec2 gravity; 														①
	gravity.Set(0.0f, -10.0f); 												②
	//创建世界
	world = new b2World(gravity); 											③
	// 允许物体是否休眠
	world->SetAllowSleeping(true);											④
	// 开启连续物理测试
	world->SetContinuousPhysics(true);										⑤
	
	//地面物体定义
	b2BodyDef groundBodyDef;											⑥
	//左下角
	groundBodyDef.position.Set(0, 0);										⑦


	//创建地面物体
	b2Body* groundBody = world->CreateBody(&groundBodyDef);						⑧


	//定义一个有边的形状
	b2EdgeShape groundBox;												⑨


	// 底部
	groundBox.Set(b2Vec2(0,0), b2Vec2(s.width/PTM_RATIO,0));						⑩
	//使用夹具固定形状到物体上
	groundBody->CreateFixture(&groundBox,0);									?


	// 顶部
	groundBox.Set(b2Vec2(0,s.height/PTM_RATIO), 
					b2Vec2(s.width/PTM_RATIO,s.height/PTM_RATIO));					
	groundBody->CreateFixture(&groundBox,0);									


	// 左边
	groundBox.Set(b2Vec2(0,s.height/PTM_RATIO), b2Vec2(0,0));							groundBody->CreateFixture(&groundBox,0);									


	// 右边
	groundBox.Set(b2Vec2(s.width/PTM_RATIO,s.height/PTM_RATIO), 
						b2Vec2(s.width/PTM_RATIO,0)); 								
	groundBody->CreateFixture(&groundBox,0);									


}

void HelloWorld::addNewSpriteAtPosition(Vec2 p)
{    
	log("Add sprite %0.2f x %02.f",p.x,p.y);


	//创建物理引擎精灵对象
	auto sprite = Sprite::create("BoxA2.png");									①
	sprite->setPosition( Vec2( p.x, p.y) );
	this->addChild(sprite);


	//物体定义
	b2BodyDef bodyDef;													②
	bodyDef.type = b2_dynamicBody;											③
	bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);							④
	b2Body *body = world->CreateBody(&bodyDef);								⑤
	body->SetUserData(sprite);												⑥


	// 定义2米见方的盒子形状
	b2PolygonShape dynamicBox;											⑦
	dynamicBox.SetAsBox(1, 1);											⑧


	// 夹具定义
	b2FixtureDef fixtureDef;												⑨
	//设置夹具的形状
	fixtureDef.shape = &dynamicBox;											⑩
	//设置密度
	fixtureDef.density = 1.0f;												?
	//设置摩擦系数
	fixtureDef.friction = 0.3f;												?
	//使用夹具固定形状到物体上	
	body->CreateFixture(&fixtureDef);										?


}

void HelloWorld::update(float dt)
{
	float timeStep = 0.03f; 
	int32 velocityIterations = 8;	
	int32 positionIterations = 1;	


	world->Step(timeStep, velocityIterations, positionIterations);


	for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())						①
	{
		if (b->GetUserData() != nullptr) {									
			Sprite* sprite = (Sprite*)b->GetUserData();	
			sprite->setPosition( Vec2( b->GetPosition().x * 
				PTM_RATIO, b->GetPosition().y * PTM_RATIO) );	
			sprite->setRotation( -1 * CC_RADIANS_TO_DEGREES(b->GetAngle()) );
		}
	}																			②
}

其中代码①~②这段代码可以同步物理引擎中的物体与精灵位置和状态。

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实例介绍Cocos2d-x中Box2D物理引擎：HelloBox2D

原文：http://blog.csdn.net/tonny_guan/article/details/39897127