high precision FPS (Python recipe) by Jiri Justra

ActiveState Code (http://code.activestate.com/recipes/579053/)

Let me share a few other implementations and ideas with you. The first is your code readied for Python 3, and the rest are self-correcting timing algorithms. They also provide errors when they cannot run the remaining code at the frames-per-second requested. My implementation of tick uses a callback to run the rest of the program, and the Timer class is can be used similarly to how you wrote your code.

import time

_tick2_frame = 0
_tick2_fps = 20000000   # real raw FPS
_tick2_t0 = time.time()

def tick(fps=60):
    global _tick2_frame, _tick2_fps, _tick2_t0
    n = _tick2_fps / fps
    _tick2_frame += n
    while n > 0:
        n -= 1
    if time.time() - _tick2_t0 > 1:
        _tick2_t0 = time.time()
        _tick2_fps = _tick2_frame
        _tick2_frame = 0

# while True:
#     tick(1)             # 1 frame per second
#     print(_tick2_fps)   # see adjustment in action
#     print(time.time())

################################################################################

def tick(fps, callback):
    frame = 0
    start = time.perf_counter()
    while True:
        callback()
        frame += 1
        target = frame / fps
        passed = time.perf_counter() - start
        differ = target - passed
        if differ < 0:
            raise ValueError('callback was too slow')
        time.sleep(differ)

# tick(60, lambda: print(time.time()))

################################################################################

class Timer:

    def __init__(self, fps):
        self.__fps = fps
        self.__frame = 0
        self.__start = None

    def tick(self):
        if self.__start is None:
            self.__start = time.perf_counter()
        self.__frame += 1
        target = self.__frame / self.__fps
        passed = time.perf_counter() - self.__start
        differ = target - passed
        if differ < 0:
            # raise ValueError('cannot maintain desired FPS rate')
            return True
        time.sleep(differ)
        return False

timer = Timer(30)
while True:
    if timer.tick():
        raise ValueError('cannot maintain desired FPS rate')
    print(time.time())

Hi, Stephen. Thanks for your comment. I am sorry, but your code seems python3-only and uses not precise time.sleep. Can you provide more in-depth explanation, pls?

Jiri - the problem for most people is that your code seems to use a busy loop, which is not ideal for many applications as wastes CPU cycles - which is not great for a multi-tasking system.

True, Tony. But this code is made for a game, where it is not much of concern. I needed precision for high fps animations. This did the job.

Did you consider using a generator to maintain the last tick timestamp? I think you could generate how long to sleep and then use different sleep functions. time.sleep is in the standard library but others may use gevent.sleep.

I created a number of games in Free Python Games at http://www.grantjenks.com/docs/freegames/ but I didn't worry too much about high-precision FPS. I just put a plain sleep(50) or whatever call in the code. There's definitely room for improvement but the simplicity is hard to beat.