Add a very basic time span API

[MatthiasWM]

For doing anything animated, it is useful to have a method to measure time spans that is independent on the actual execution time of timeout-callbacks. I would like to add Fl::time_now_ms() and Fl::time_span_ms(t0, t1=0) in a cross-platform way.

http://www.firstobject.com/getmillicount-milliseconds-portable-c++.htm

[MatthiasWM]

See: fl_gettime(long*, long*); in FL/forms.H and Fl::system_driver()->gettime(&sec, &usec);, also static double elapsed_time() in Fl_Timeout.H which is not public.

[Albrecht-S]

Yes, the one in Fl_Timeout is not public and I looked for a better solution at that time. I'd like to see a method that can be used reliably also in timeout handling. IIRC the problem was (as most of the time ;-) ) Windows.

Without using multimedia timers it's hard to find a Windows function that can reliably deliver a timer stamp that doesn't wrap around after some time (maybe 49 days IIRC, too lazy to check or calculate now). This must be taken into account for such a delta time calculation.

I remember that I also found this getmillicount stuff, it might be worth a look.

... just took a quick look, it's "public domain", seems like we could use it.

Anyway, if you can find a proper solution:

+1 👍 for such a new feature.

[MatthiasWM]

Brainstorm for myself:

• FL_Point_In_Time or Fl_Timepoint or Fl_Time_Point as an abstract type, so users don't expect a time or date

• FL_Point_In_Time Fl::now() sets the time now as a point in time, alternative Fl::time_now()

• double Fl::seconds_since(FL_Point_In_Time some_time_earlier) returns the elapsed time between now and earlier

• maybe long Fl::ticks_since(FL_Point_In_Time some_time_earlier) returns the elapsed time in 60th of a second

• possibly ms_since() because milliseconds are relatively common

• double Fl::seconds_between(FL_Point_In_Time a, FL_Point_In_Time b) may be useful, and ticks_between

• I don't want to publish any calendar or time-of-day functionality here, or make the user issue that he can derive a time of day from FL_Point_In_Time.

• I want to avoid using timer because we already use the timer callbacks, and this is not directly related.

• I don't want to use chromo either, because we don't emulate C++11 std::chronologically either.

• I don't think that returning a timer resolution or precision is needed if we promise to be at least a common screen frame rate. This is not meant to be a performance timer, but to be used to time animations.

[MatthiasWM]

Implemented in PR #670