Fixed timestep

gistfile1.c

int main(void)
{
    int frames = 0;
    double fpstimer;
    double ticktimer = 0.0;
    double last;

    last = dtime();
    while (1) {
        double now = getTime();
        double dt = now - last;
        last = now;

        // they need to advance with the same frame delta
        ticktimer += dt;
        fpstimer += dt;
        
        // 128fps
        if (ticktimer >= 1.0/128.0) {
            ++frames;
            ticktimer -= 1.0/128.0;
            // should not reset to 0, you might have uneven residue left
            // so you should decrease by exactly one timestep
        }
        if (fpstimer >= 1.0) {
            printf("fps: %d\n", frames);
            frames = 0;
            fpstimer -= 1.0;
        }
    }

    return 0;
}