gameplay理解

Camera视角：确定显示的视场及视角。

Game：显示的基类。静态单例模式。但是获取方式很奇怪。

Game::getInstance得到的是__gameInstance，但是__gameInstance是在Game（）构造函数里=this。因此如果没有Game的实例，this就是NULL。

然而使用时，编写继承自Game的子类，如HomuraGame，并且声明HomuraGame的全局变量，这样在加载该so时子类的实例就会创建，同时Game也就会创建。而后调用时Game::getInstance就能得到Game的指针。

这也意味着同一时间只能存在一个Game的实例进行操作。

 Game::Game()
     : _initialized(false), _state(UNINITIALIZED), _pausedCount(),
       _frameLastFPS(), _frameCount(), _frameRate(), _width(), _height(),
       _clearDepth(1.0f), _clearStencil(), _properties(NULL),
       _animationController(NULL), _audioController(NULL),
       _physicsController(NULL), _aiController(NULL), _audioListener(NULL),
       _timeEvents(NULL), _scriptController(NULL), _scriptTarget(NULL)
 {
     GP_ASSERT(__gameInstance == NULL);

     __gameInstance = this;
     _timeEvents = new std::priority_queue<TimeEvent, std::vector<TimeEvent>, std::less<TimeEvent> >();
 }

 Game::~Game()
 {
     SAFE_DELETE(_scriptTarget);
     SAFE_DELETE(_scriptController);

     // Do not call any virtual functions from the destructor.
     // Finalization is done from outside this class.
     SAFE_DELETE(_timeEvents);
 #ifdef GP_USE_MEM_LEAK_DETECTION
     Ref::printLeaks();
     printMemoryLeaks();
 #endif

     __gameInstance = NULL;
 }

 Game* Game::getInstance()
 {
     GP_ASSERT(__gameInstance);
     return __gameInstance;
 }

     /**
      * Constructor.
      */
     Game();

     /**
      * Destructor.
      */
     virtual ~Game();

     /**
      * Gets the single instance of the game.
      *
      * @return The single instance of the game.
      */
     static Game* getInstance();

 #define DISPATCH_EVENT(dispatch, count, eventName, ...) { \
     for (int i = ; i < count; i++) { \
         EXECUTE_FUNCTION(dispatch[i], eventName, __VA_ARGS__); \
     } \
 }

 HomuraGame game;

 HomuraGame::HomuraGame() : mParticleIndex(), mGraphicsIndex(), pFont(NULL) {
     memset(pParticle, , MAX_HOMURA_SIZE * sizeof(Homura*));
     memset(pGraphics, , MAX_HOMURA_SIZE * sizeof(Homura*));
     memset(pPhysical, , MAX_HOMURA_SIZE * sizeof(Homura*));
 }

而后Game的子类中实现了update和render方法，openGL中每次更新都会调用Game的frame方法，而frame方法会调用update及render方法，从而对动画进行更新。

 class HomuraGame : public Game {
 public:
     HomuraGame();

     /**
      * @see Game::initialize
      */
     void initialize();

     /**
      * @see Game::finalize
      */
     void finalize();

     /**
      * @see Game::update
      */
     void update(float elapsedTime);

     /**
      * @see Game::render
      */
     void render(float elapsedTime);

     void resizeEvent(unsigned int width, unsigned int height);

     void keyEvent(Keyboard::KeyEvent evt, int key);

     void touchEvent(Touch::TouchEvent evt, int x, int y, unsigned int contactIndex);

     bool mouseEvent(Mouse::MouseEvent evt, int x, int y, int wheelDelta);

     static HomuraGame* getInstance();