SDL/OpenGL game runs too fast on 144Hz screen; can't use vsync

Question

This is how I handle the game loop:

while (running) {
    diff = duration_cast<milliseconds>(end - start).count();
    start = clock::now();

    dt = diff / (16.0);

    handleInput(); // get input
    update(dt); // game logic
    render(); // render game

    SDL_GL_SwapWindow(window); // swap frame buffer

    end = clock::now();
}

It is intended to be a fixed timestep game locked to 60FPS (it's a re-made emulation of an SNES game) however it runs on 144 timestep on my 144hz screen, making it far too fast. Vsync can't solve this, so what can?

Answer 1

Here is a quick example of how game loop can be implemented:

int32_t tickInteval = 1000/FPS; // frequency in Hz to period in ms
uint32_t lastUpdateTime = 0;
int32_t deltaTime = 0;
while (running) { // running condition
    uint32_t currentTime = SDL_GetTicks();
    deltaTime = currentTime - lastUpdateTime;

    int32_t timeToSleep = tickInteval - deltaTime;
    if(timeToSleep > 0)
    {
        SDL_Delay(timeToSleep); // energy saving
    }

    update(deltaTime); // game logic
    lastUpdateTime = currentTime;
}

I would recommend to look close on this topic.

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UPD.
One might be concerned with uint32_t overflow. And yes it will overflow. After almost two months of uninterrupted run of the game (49.7 days to be precise). What will happen then? currentTime will be a very small positive integer, lastUpdateTime will be a very large positive integer. But the subtraction of two will not overflow no matter what. Moreover if the difference does not fit into int32_t it will be wrapped around modulo of UINT_MAX + 1 resulting in a small positive integer that will be the exact number of ticks these two values different (with regard to unsigned overflow of one).