How to calculate FPS in OpenGL?

Question

void CalculateFrameRate()
{    
    static float framesPerSecond    = 0.0f;       // This will store our fps
    static float lastTime   = 0.0f;       // This will hold the time from the last frame
    float currentTime = GetTickCount() * 0.001f;    
    ++framesPerSecond;
    if( currentTime - lastTime > 1.0f )
    {
        lastTime = currentTime;
        if(SHOW_FPS == 1) fprintf(stderr, "\nCurrent Frames Per Second: %d\n\n", (int)framesPerSecond);
        framesPerSecond = 0;
    }
}

Should I call this function in void play(void) or void display(void)?

Or it does not make any difference?

What is `play(void)`? Note that things are a bit more complicated since GPUs are unpredictable: http://stackoverflow.com/questions/8779936/correct-way-to-calculate-the-fps — Ciro Santilli OurBigBook.com, Mar 17 '16 at 08:16

score 7 · Accepted Answer · edited Aug 02 '20 at 12:09

7

You should put it in the display loop. Here's an article that explains some intricacies of game loops that you should read.

edited Aug 02 '20 at 12:09

Philipp Zettl

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answered Apr 11 '11 at 21:34

DShook

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epatel · Answer 2 · 2011-04-11T21:44:40.640

1

If you have any kind of synchronization routine I suggest you place the call just after that, ie prior the big calculations. Otherwise the timing calculations can be shaky and give different values each loop...and a note, it's better to have a steady FPS than a fluctuating FPS just to maximize it. The fluctuation even so subtle makes the viewer/player aware that it's all a game and the immersion is lost.

edited Apr 11 '11 at 21:44

answered Apr 11 '11 at 21:37

epatel

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score 0 · Answer 3 · answered Jan 01 '20 at 20:28

void CalculateFrameRate()
{
    static float framesPerSecond = 0.0f;
    static int fps;
    static float lastTime = 0.0f;
    float currentTime = GetTickCount() * 0.001f;
    ++framesPerSecond;
    glPrint("Current Frames Per Second: %d\n\n", fps);
    if (currentTime - lastTime > 1.0f)
    {
        lastTime = currentTime;
        fps = (int)framesPerSecond;
        framesPerSecond = 0;
    }
}

score 0 · Answer 4 · answered Jun 04 '22 at 07:42

Call this in every frame:

int _fpsCount = 0;
int fps = 0; // this will store the final fps for the last second

time_point<steady_clock> lastTime = steady_clock::now();

void CalculateFrameRate() {
    auto currentTime = steady_clock::now();

    const auto elapsedTime = duration_cast<nanoseconds>(currentTime - lastTime).count();
    ++_fpsCount;

    if (elapsedTime > 1000000000) {
        lastTime = currentTime;
        fps = _fpsCount;
        _fpsCount = 0;
        
        fmt::print("{} fps\n", fps); // print out fps in every second (or you can use it elsewhere)
    }
}

You can access the fps value from the fps variable, or you can print it only once a second as it's in the code currently.

How to calculate FPS in OpenGL?

4 Answers4

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