Box2d物理引擎实战开发（共6部分）

第四阶段：功能扩展1

1.Box2d物理引擎：Box2d介绍 

  官网http://box2d.org/

定义NDK_ROOT   终端打开proj.android 然后  sudo nano /etc/profile回车输入密码  export NDK_ROOT=

eclipse-sdks- android -android-ndk-r9c- ndk-build右键的路径 之后 退出-保存 重启终端

2.Box2d物理引擎：创建世界

HelloWorldScene.h中

#include<Box2D/Box2D.h>

private:

    b2World *world;

public:

    virtualvoidupdate(floatdt);

HelloWorldScene.cpp中

HelloWorld::init()中：

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

// float32 timeStep模拟物理世界一步一步之间的时间差 这里用每帧之间的时间差dt     

// int32 velocityIterations数据迭代（重新计算的次数来避免误差） 次数越多越精确但也耗费资源 官方定为8

// int32 positionIterations 位置迭代官方建议为3

voidHelloWorld::update(floatdt){

    world->Step(dt, 8, 3);

}

3.Box2d物理引擎：创建运动的物体

 glview->setDesignResolutionSize(800,600, ResolutionPolicy::SHOW_ALL);

b2_staticBody = 0静态的物体

b2_kinematicBody漂浮的物体

b2_dynamicBody 动态的物体

4.Box2d物理引擎：创建静止的物体

5.Box2d物理引擎：创建漂浮的物体

6.Box2d物理引擎：物体碰撞检测

#include"cocos2d.h"
#include <Box2D/Box2D.h>


#define RATIO80.0f

classHelloWorld : public cocos2d::Layer,publicb2ContactListener
{
   
private:
    b2World *world;
    b2Body *groundBody;
   
public:
    // there's no 'id' in cpp, so we recommend returning the class instance pointer
    static cocos2d::Scene* createScene();

    // Here's a difference. Method 'init' in cocos2d-x returns bool, instead of returning 'id' in cocos2d-iphone
    virtual bool init(); 
   
    // a selector callback
    void menuCloseCallback(cocos2d::Ref* pSender);
   
    virtual void update(floatdt);
   
    virtual void BeginContact(b2Contact* contact);
   
    void addRect(floatx,floaty,b2BodyType type);
    void addGround();
   
    // implement the "static create()" method manually
    CREATE_FUNC(HelloWorld);

};

#include"HelloWorldScene.h"

USING_NS_CC;

Scene* HelloWorld::createScene()
{
    // 'scene' is an autorelease object
    auto scene = Scene::create();
   
    // 'layer' is an autorelease object
    auto layer = HelloWorld::create();
   
    // add layer as a child to scene
    scene->addChild(layer);
   
    // return the scene
    return scene;
}

// on "init" you need to initialize your instance
boolHelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !Layer::init() )
    {
        return false;
    }
   
    world = new b2World(b2Vec2(0,-10));
    world->SetContactListener(this);
   
   
    addGround();
    addRect(5,3, b2_dynamicBody);
//    addRect(1,5,b2_kinematicBody);
   
    scheduleUpdate();
   
    return true;
}

voidHelloWorld::update(floatdt){
    world->Step(dt, 8, 3);
   
    Sprite *s;
   
    for (b2Body *b = world->GetBodyList(); b; b=b->GetNext()) {
       
        if (b->GetUserData()) {
            s = (Sprite*)b->GetUserData();
           
            s->setPosition(b->GetPosition().x*RATIO, b->GetPosition().y*RATIO);
        }
    }
}

voidHelloWorld::BeginContact(b2Contact *contact){
    if (contact->GetFixtureA()->GetBody()==groundBody||contact->GetFixtureB()->GetBody()==groundBody) {
       
        log("有物体落在了地板上");
    }
}


voidHelloWorld::addRect(floatpositionX,floatpositionY,b2BodyType type){
   
    //config box2d
    b2BodyDef def;
    def.position = b2Vec2(positionX, positionY);
    def.linearVelocity = b2Vec2(0,10);
    def.type = type;
   
    b2Body* body = world->CreateBody(&def);
   
    b2PolygonShape shape;
    shape.SetAsBox(0.5,0.5);
   
    b2FixtureDef fixtureDef;
    fixtureDef.density = 1;
    fixtureDef.friction = 0.3;
    fixtureDef.shape = &shape;
    body->CreateFixture(&fixtureDef);
   
    //config cocos shape
    auto s = Sprite::create();
    s->setTextureRect(Rect(0,0,0.5*2*RATIO,0.5*2*RATIO));
    addChild(s);
   
    body->SetUserData(s);
}


voidHelloWorld::addGround(){
   
    b2BodyDef def;
    def.position = b2Vec2(400/RATIO,0);
    def.type = b2_staticBody;
   
    groundBody = world->CreateBody(&def);
   
    b2PolygonShape groundShape;
    groundShape.SetAsBox(400/RATIO,0.5);
   
    b2FixtureDef fixureDef;
    fixureDef.density = 1;
    fixureDef.friction = 0.3;
    fixureDef.shape = &groundShape;
    groundBody->CreateFixture(&fixureDef);

}