On 22.02.2009, at 02:03, Chang Yuan wrote: > I'm using Fl (v1.3) timeout functions to get accurate frame rate > control under Windows. I followed the documentation to use > Fl::add_timeout and Fl::repeat_timeout with the same time interval, > e.g. 30 milliseconds. However, the callback function is not executed > at the expected intervals. I used QueryPerformanceCount to get the > execution time and found that FLTK's timeout function is always > behind my expected intervals, say around 35 msecs to 40 msecs. Even > if I decrease the time interval to an insane value, FLTK can only > reach up to ~40fps. Is this a bug or the limitation of the current > version (v1.3)? Will v2.0 do better on this?
First of all, MS Windows is by no means a real time operating system. Any timing efforts in the millisecond range a futile. Even in the range of seconds, I would not expect MS Windows to schedule a proscess for me. Other appilcations may steal all available time, and the OS has no provision to keep them from doing that. The same is true for Linux and OS X. The FLTK timeout functions rely on the internal timers of the OS. The MS Windows timers depend on a few hardware factors, but usually have a resolution between 10 and 40ms (hence the 40 fps you are seeing). But even then, there is no guarantee that your application will actually receive on of these slots. "QueryPerformanceCount" on the other hand *is* very high precission, but that is merely a counter, not a timer. This would all be a desaster for multimedia and video applications. MS Windows has creates a huge bunch of libraries and implemented tons of extra hadware to get around those basic limitations. Linux uses a slightly different approach, and OS X is somewhere in the middle of all this. So if you are planning to play a video in FLTK< you would have to fall back to one of those native video libraries and use their timing and rendering functions. Matthias ---- http://robowerk.com/ _______________________________________________ fltk-bugs mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk-bugs
