Why is Time.fixedTime and family a float and not a double?

Question

Just want know if I'm missing something. I'm from ObjC land where NSTimeInterval is a double, which gives "sub-millisecond precision within a range of 10,000 years". Compare this to Unity, which since it uses a float for time, starts to break down after a day (maybe even sooner). Math.Approximately(1 day, a day + 1 frame) returns true for example (whereas 1 hour vs 1 hour + 1 frame correctly returns false). I actually experienced this when I left my game open all night and came back to it, noticing strange behavior on things that were time dependent.

Answer 1

Unity internally uses a double to track time. The double is converted to a float before being passed to user code.

This is largely because Unity uses floats in most other locations (floats are much better supported on a range of graphics cards/platforms).

Since Unity uses a double internally, you don't need to worry about it losing count / failing to increment time.

What you do need to worry about is that after the game has been running for a number of hours, the representable values become more and more sparse.

This can cause things that moved smoothly to start stuttering.

Personally, I tend to keep my own (float) and reset it to zero at some sensible interval, ideally when it makes no difference (which depends what you're using it for).