You can further increase the smoothness of Delta Time by setting a target number of FPS ( in this case 40 ) and using delay until the required number of milliseconds have passed and it's time to flip. You have to use flip false with this method, but basically you get all the advantages of Delta Time if the target machine is not capable of achieving the desired frame rate, but you also free up system time for windows to do it's thing on systems which can achieve 40fps or more, which eliminates those windowed-mode glitches where the system takes over for a split second and causes a drop in frame rate.