游戏有三种状态，准备开始、游戏中、游戏结束，定义一个枚举来表示：

/** * The status of game,it has three status. */
typedef enum tag_GameState {
  /** The game hasn't started,but ready to start */
  kGameStateReady = 1,/** The game has started,and the player is playing the game */
  kGameStateStarted,/** The game has over,it means that the player has lost */
  kGameStateOver
} GameState;

游戏层与控制层需要通信，因此要遵守代理协议：

class GameScene : public cocos2d::Layer,public OptionDelegate

代理协议只有一个方法，就是点击屏幕事件监听回调：

/** * The OptionDelegate method override */
  void onTouch();

游戏层还需要与状态层通信，因此需要接收一个代理：

/** * The delegate of status. * When is setted,it will call StatusDelegate corresponding method on correct * time. */
  CC_SYNTHESIZE(GameStatusDelegate*,_statusDelegate,StatusDelegate);

把状态层对象作为代理传到游戏层，就可以二者通信了。

下面看下初始化方法，这个是很重要的，添加物理特性，并监听触碰事件：

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

  auto size = Director::getInstance()->getVisibleSize();
  auto origin = Director::getInstance()->getVisibleOrigin();

  // Add the bird
  auto bird = BirdSprite::getInstance();
  bird->createBird();
  auto body = PhysicsBody::create();
  body->addShape(PhysicsShapeCircle::create(kBirdRadius));
  body->setDynamic(true);
  body->setLinearDamping(0.0f);
  body->setGravityEnable(false);
  body->setCategoryBitmask(0x01);
  body->setCollisionBitmask(0x01);
  body->setContactTestBitmask(0x01);
  bird->setPhysicsBody(body);
  bird->setPosition(origin.x + size.width / 3 - 5,origin.y + size.height / 2 + 5);
  bird->setActionState(kActionStateIdle);
  this->addChild(bird);

  // Add the ground
  _groundNode = Node::create();
  auto groundBody = PhysicsBody::create();
  auto groundSize = Size(kDesignWidth,BackgroundLayer::getLandHeight());
  groundBody->addShape(PhysicsShapeBox::create(groundSize));
  groundBody->setDynamic(false);
  groundBody->setLinearDamping(0.0f);
  groundBody->setCategoryBitmask(0x01);
  groundBody->setContactTestBitmask(0x01);
  groundBody->setCollisionBitmask(0x01);
  _groundNode->setPhysicsBody(groundBody);
  _groundNode->setPosition(groundSize.width / 2,groundSize.height);
  this->addChild(_groundNode);

  // land
  // Add the land1 and land2
  _land1 = Sprite::createWithSpriteFrame(AtlasLoader::getInstance()->getSpriteFrame("land"));
  _land1->setAnchorPoint(Vec2::ZERO);
  _land1->setPosition(Vec2::ZERO);
  this->addChild(_land1,30);

  _land2 = Sprite::createWithSpriteFrame(AtlasLoader::getInstance()->getSpriteFrame("land"));
  _land2->setAnchorPoint(Vec2::ZERO);
  _land2->setPosition(Vec2(_land1->getContentSize().width - 2.0f,0));
  this->addChild(_land2,30);

  // Add a timer to update the land
  _shiftLand = schedule_selector(GameScene::scrollLand);
  this->schedule(_shiftLand,0.01f);

  // will call update(float delta) method
  this->scheduleUpdate();

  // Add contact listener
  //
  // If body->getCategoryBitmask() & groundBody->getContactTestBitmask() == 1
  // Then we can listen the physics touch event,otherwise not.
  //
  // If body->getCategoryBitmask() & groundBody->getCollisionBitmask() == 1
  // Then the bird and the ground can collide,otherwise not.
  auto listener = EventListenerPhysicsContact::create();
  listener->onContactBegin = CC_CALLBACK_1(GameScene::onContactBegin,this);
  this->getEventDispatcher()->addEventListenerWithSceneGraPHPriority(listener,this);

  return true;
}

要想让A和B能够在相碰时，发出事件，规则如下：
// If body->getCategoryBitmask() & groundBody->getContactTestBitmask() == 1
// Then we can listen the physics touch event,otherwise not.
要想让A和B能够发生冲突并发出事件，规则如下：
//
// If body->getCategoryBitmask() & groundBody->getCollisionBitmask() == 1
// Then the bird and the ground can collide,otherwise not.

如果不添加，默认情况下是不会监听到的，刚开始我就遇到此问题，然后通过百度才明白原因。

下面是创建场景，需要把背景层、控制层、状态层、游戏层添加到场景中：

Scene* GameScene::createScene() {
  // create a scene with physics world
  // 场景需要使用物理世界来创建，否则添加的物理特性就无效
  auto scene = Scene::createWithPhysics();
  if (scene->getPhysicsWorld()) {
    scene->getPhysicsWorld()->setGravity(Vect(0,-900));
  } else {
    CCLOG("Error: Game scene get physics world,but it is nullptr");
  }

  // background layer
  auto backgroundLayer = BackgroundLayer::create();
  if (backgroundLayer) {
    scene->addChild(backgroundLayer);
  }

  // game layer
  auto gameLayer = GameScene::create();
  // status layer
  auto statusLayer = StatusLayer::create();

  if (gameLayer) {
    gameLayer->setPhysicsWorld(scene->getPhysicsWorld());
    // 游戏层与状态层是需要通信的，把状态层作为游戏层的代理 
    gameLayer->setStatusDelegate(statusLayer);
    gameLayer->setTag(kGameLayerTag);
    scene->addChild(gameLayer);
  }
  if (statusLayer) {
    scene->addChild(statusLayer);
  }

  // option layer
  auto optionLayer = OptionLayer::create();
  if (optionLayer) {
  // 状态层与游戏层是需要通信的，把游戏层作为状态层的代理
    optionLayer->setOptionDelegate(gameLayer);
    scene->addChild(optionLayer);
  }

  return scene;
}

添加水管，给水管也添加物理特性，就可以让小鸟与水管在接触时，发出相碰事件

void GameScene::createPipes() {
  // create pipes
  auto size = Director::getInstance()->getVisibleSize();
  for (int i = 0; i < kPipePairCount; ++i) {
    auto pipeUp = Sprite::createWithSpriteFrame(AtlasLoader::getInstance()->getSpriteFrame("pipe_up"));
    //pipeUp->setPosition(0,<#float y#>)
    auto pipeDown = Sprite::createWithSpriteFrame(AtlasLoader::getInstance()->getSpriteFrame("pipe_down"));
    pipeDown->setPosition(0,kPipeHeight + kPipeUpDownDistance);

    auto pipeNode = Node::create();
    pipeNode->setPosition(size.width + i * kPipeInterval + kWaitDistance,getRandomPipeHeight());
    pipeNode->addChild(pipeDown,0,kPipeDownTag);
    pipeNode->addChild(pipeUp,kPipeUpTag);

    // Add physics to pipe
    auto body = PhysicsBody::create();
    auto Box = PhysicsShapeBox::create(pipeDown->getContentSize(),PHYSICSSHAPE_MATERIAL_DEFAULT,Vec2(0,kPipeHeight + kPipeUpDownDistance));
    body->addShape(Box);
    body->addShape(PhysicsShapeBox::create(pipeUp->getContentSize()));
    body->setDynamic(false);
// If body->getCategoryBitmask() & 小鸟的物理body>->getCollisionBitmask() == 1
// 小鸟与水管接触才会发出事件
    body->setCategoryBitmask(0x01);
    body->setContactTestBitmask(0x01);
    body->setCollisionBitmask(0x01);

    pipeNode->setPhysicsBody(body);
    pipeNode->setTag(kPipeNewTag);
    this->addChild(pipeNode);

    _pipes.pushBack(pipeNode);
  }
}

小鸟通过水管检测：

void GameScene::checkHit() {
  for (auto pipe : _pipes) {
    if (pipe->getTag() == kPipeNewTag) {
      // 通过一根
      if (pipe->getPositionX() < BirdSprite::getInstance()->getPositionX()) { CocosDenshion::SimpleAudioEngine::getInstance()->playEffect("sfx_point.ogg");

        ++_currentscore;

        if (this->getStatusDelegate()) {
          this->getStatusDelegate()->onGamePlaying(_currentscore);
        }

        pipe->setTag(kPipePassedTag);
      }
    }
  }
}

通过遍历所有水管，如果当前是显示在屏幕上新的水管，再判断与小鸟的X坐标，来判断小鸟是否通过了水管。 当通过后，又把水管设置为已经通过的水管，如此重复使用。