David Megginson wrote: > > Jon Berndt writes: > > > I was remembering first how the F-16 sim at Link was run at 25 Hz, which > > is of course 0.04 seconds. Wait ... (thinking, this time). Yes, that's > > right ;-) > > Then, I went to the numpad on my keyboard and hit 0.01 as I was typing in > > the dt for 100 Hz. Only I missed. On purpose or accident I am not sure. > > Currently, we have > > FGSubsystem::update (int dt) > > where dt represents the elapsed time in ms since the last update. That > puts a limit of 2^31 ms, or just under 600 hours, between updates. It > has the advantage of keeping us in integer math, and the disadvantage > of not being able to represent a granularity of under 1ms. That's OK > for a simulator involving human interaction, since we cannot notice > such a small difference, but it would obviously be a problem for other > kinds of simulations such as rapid chemical reactions.
As soon as something depends on the dt it's quite likely that it involves floats. And one of the most common uses of dt is for integration. As integration "summs the values up" one wrong value is enough to make all following results wrong, too (*). So I want (as I wrote some time ago, too), that a float or double dt in the unit second gets passed to the update functions/methods. > So, what do we do? John mentioned that reporting in sec rather than > ms is standard, so do we switch to > > FGSubsystem::update (double dt_sec) Yes > or do we simply rename dt to elapsed_ms > > FGSubsystem::update (int elapsed_ms) > No, there we'll get problems when we need a accurate "dt". And offering a int elapsed_ms as well as a double dt doesn't make much sense IMHO. > or do stick with ms but allow finer granularity > > FGSubsystem::update (double elapsed_ms) No. Stick to the standard. And when I get ms I probably still want sec (or hour or µs or whatever). So let the modules do the work to get the correctly shaped value, we can only guess (and guess it wrong) > ? I don't see any harm in sticking with the integer value, I do. > but I > agree that a better name, proper documentation, and some debugging is > essential. That's definitely a requirement. CU, Christian -- The idea is to die young as late as possible. -- Ashley Montague Whoever that is/was; (c) by Douglas Adams would have been better... _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
