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(0),
      _frameLastFPS(0), _frameCount(0), _frameRate(0), _width(0), _height(0),
      _clearDepth(1.0f), _clearStencil(0), _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 = 0; i < count; i++) { 
        EXECUTE_FUNCTION(dispatch[i], eventName, __VA_ARGS__); 
    } 
}

HomuraGame game;

HomuraGame::HomuraGame() : mParticleIndex(3), mGraphicsIndex(1), pFont(NULL) {
    memset(pParticle, 0, MAX_HOMURA_SIZE * sizeof(Homura*));
    memset(pGraphics, 0, MAX_HOMURA_SIZE * sizeof(Homura*));
    memset(pPhysical, 0, 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();