FPS на OpenGL

class fps_timer
{
private:
    float resolution;
    bool performance_timer;
    unsigned long mm_timer_start, mm_timer_elapsed;
    __int64 frequency, performance_timer_start, performance_timer_elapsed;

public:
    fps_timer()
    {
        ZeroMemory( this, sizeof( fps_timer ) );

        if (!QueryPerformanceFrequency( (LARGE_INTEGER *)&frequency ))
        {
            performance_timer = false;
            mm_timer_start = timeGetTime();
            resolution = 1.f / 1000.f;
            frequency = 1000;
            mm_timer_elapsed = mm_timer_start;
        }
        else
        {
            QueryPerformanceCounter( (LARGE_INTEGER *)&performance_timer_start );
            performance_timer = true;
            resolution = (float)(((double)1.0) / ((double)frequency));
            performance_timer_elapsed = performance_timer_start;
        }
    }

    ~fps_timer()
    {
    }

    float TimerGetTime()
    {
        __int64 time;

        if (performance_timer)
        {
            QueryPerformanceCounter((LARGE_INTEGER *) &time);
            return ((float)(time - performance_timer_start) * resolution) * 1000.f;
        }

        return ((float)(timeGetTime() - mm_timer_start) * resolution) * 1000.f;
    }
};

...
fps_timer fps;

#define MAX_COUNT   15
int fcount = 0;
DWORD fr = 0, curfr = 0;

void update_scene()
{
...

    float f = fps.TimerGetTime();

... тут прорисовка сцены ...

    if(fcount < MAX_COUNT)
    {
    fr += (DWORD)((1000.f - ((fps.TimerGetTime() - f) * 10.f)) - 500.f);
    fcount++;
    }
    else
    {
    curfr = fr / MAX_COUNT;
    fr = fcount = 0;
    }

    // тут curfr показывает текущее значение FPS
...
}