cocos2dx_GLProgramStateCache

缓存GLProgramState。reuse the old GLProgramState, which will accelerate the creation of game objects such as sprites, particles etc.

class CC_DLL GLProgramStateCache
{
public:
    static GLProgramStateCache* getInstance();
    static void destroyInstance();
    GLProgramState* getGLProgramState(GLProgram* program);    // 没有则将为这个program创建ProgramState
    void removeAllGLProgramState();
    void removeUnusedGLProgramState();        // referenceCount == 1
protected:
    GLProgramStateCache();
    ~GLProgramStateCache();
    // key:        gl program object
    // value:    program对应的program state
    // 注意是cocos2d::Map类型，因此只要缓存了programState，那么就不必担心program的生命周期。
    Map<GLProgram*, GLProgramState*> _glProgramStates;
    static GLProgramStateCache* s_instance;
};