Am I calculating my FPS correctly?

问题

So I was wondering if I'm calculating my FPS correctly:

Uint32 delayFrom(float startTime, float endTime){
    return(endTime - startTime );
}


int main(){
    int numFrames = 0;
    Uint32 startTime = SDL_GetTicks();
    while(!done){
        frameTime = 0;
        float fps = ( numFrames/(float)(SDL_GetTicks() - startTime) )*1000;
        cout << fps << endl;
        SDL_Delay(delayFrom(frameTime, 1/60));
        ++numFrames;
    }
}

回答1:

int main() {
  int numFrames = 0;
  Uint32 startTime = SDL_GetTicks();
  while (!done) {
    ++numFrames;
    Uint32 elapsedMS = SDL_GetTicks() - startTime; // Time since start of loop
    if (elapsedMS) { // Skip this the first frame
      double elapsedSeconds = elapsedMS / 1000.0; // Convert to seconds
      double fps = numFrames / elapsedSeconds; // FPS is Frames / Seconds
      cout << fps << endl; 
    }
    SDL_Delay(1.0/60.0); // Use floating point division, not integer
  }
}

回答2:

frameTime never gets assigned anything other than 0. Presumably that's an error.

回答3:

cout could be slow so to get more precise value you need to split the time measurement and the output the result.

int main(){
    int numFrames = 0;    
    long totalTime = 0;
    while(!done){
        // measure time
        const Uint32 startTime = SDL_GetTicks();
        SDL_Delay( 1.0f/60.0f );
        const Uint32 endTime = SDL_GetTicks();

        // calculate result
        totalTime += endTime - startTime;
        ++numFrames;
        float fps = numFrames / (totalTime / 1000.0);
        cout << fps << endl;
    }
}

来源：https://stackoverflow.com/questions/5614018/am-i-calculating-my-fps-correctly