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List: flightgear-devel
Subject: Re: [Flightgear-devel] Time warping
From: Anton Gomez Alvedro <galvedro () gmail ! com>
Date: 2013-10-30 13:08:32
Message-ID: CAOCt1VoKSsauMqjHvF544FzH=spaZk6mYnXj6shqxnsu8j_hzg () mail ! gmail ! com
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> but nothing anywhere says that it should represent either of those things
Yes, that's right :)
Anyway, this started with the question of: how do you know how much
simulated time has elapsed since your last visit? If you can check every
frame, that quantity becomes sim/elapsed-sec * sim/speed-up. At least from
the aircraft point of view. But if you are updating at 10 Hz for example,
then you can not know exactly. (Or perhaps there is a different property
that exposes that value, that I haven't seen).
If there is a feeling that time management could be improved, I would be
happy to have a look at it. But of course if we can agree on how the user
experience should look like.
Anton
P.S. Just in case: I do realize this is a rather critical/sensible part of
the sim. :)
On Wed, Oct 30, 2013 at 11:44 AM, James Turner <zakalawe@mac.com> wrote:
>
> On 30 Oct 2013, at 10:33, Anton Gomez Alvedro <galvedro@gmail.com> wrote:
>
> I don't know! :D It looked like so after this short discussion:
> http://forum.flightgear.org/viewtopic.php?f=14&t=21020&start=30#p192454
>
> The comments in the code suggest a different concept however:
>
> class FGGlobals {
> ...
> // Number of milliseconds elapsed since the start of the program.
> double sim_time_sec;
>
> But the name given to the variable again suggests "simulated time in
> seconds", not milliseconds since start.
>
>
> To be honest I wish we did not have those cumulative values - the comments
> are wrong, the property names are misleading. For 'real' dt (not simulated)
> we can of course offer elapsed seconds or msec since the program started,
> but I can't imagine many use cases where that's a genuinely interesting
> value.
>
> In practice, the variable doesn't grow when the simulator is paused, so
> the comment doesn't really hold, and it doesn't honour either speed-up nor
> warp settings, so it doesn't represent simulated time inside nor outside
> the aircraft. ??? :D
>
>
> No, but nothing anywhere says that it should represent either of those
> things (unless we have even more misleading comments or docs?)
>
> If it is not a bug, I guess we can agree that the context surrounding this
> property is, at least, confusing.
>
>
> Very likely.
>
> Personally, I tend to agree with James' explanation. It makes sense to me,
> assuming the ability to warp environment time independently of local
> aircraft time is a feature. How each system should interact with this
> concept, even how both timelines should interact to each other, I guess
> that requires careful thinking.
>
>
> Note I figured out that explanation by reading the code and guessing, it's
> not based on anything 'official' :)
>
> I tend to agree with what Torsten wrote - given that these are unphysical
> things we're doing, there are lots of differing use cases and any link
> between 'speed-up' and 'warp' is likely to be problematic. I do think
> including speed-up in sim-dt would be valuable, if it could be done safely,
> but I'd want to see a pretty convincing audit of Nasal/ and fgdata/Aircraft
> to establish how the value is being used and what kind of / quantity of
> bugs we might produce by making such a change.
>
> Kind regards,
> James
>
>
>
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>
[Attachment #5 (text/html)]
<div dir="ltr"><span style="font-family:arial,sans-serif;font-size:13px">> but \
nothing anywhere says that it should represent either of those \
things</span><br><div><span style="font-family:arial,sans-serif;font-size:13px"><br> \
</span></div><div style><span \
style="font-family:arial,sans-serif;font-size:13px">Yes, that's right \
:)</span></div><div style><br></div><div style><font face="arial, sans-serif">Anyway, \
this started with the question of: how do you know how much simulated time has \
elapsed since your last visit? If you can check every frame, that quantity becomes \
sim/elapsed-sec * sim/speed-up. At least from the aircraft point of view. But if you \
are updating at 10 Hz for example, then you can not know exactly. (Or perhaps there \
is a different property that exposes that value, that I haven't \
seen).</font></div> <div style><font face="arial, sans-serif"><br></font></div><div \
style><font face="arial, sans-serif">If there is a feeling that time management could \
be improved, I would be happy to have a look at it. But of course if we can agree on \
how the user experience should look like.</font></div> <div style><font face="arial, \
sans-serif"><br></font></div><div style><font face="arial, \
sans-serif">Anton</font></div><div style><font face="arial, \
sans-serif"><br></font></div><div style><font face="arial, sans-serif">P.S. Just in \
case: I do realize this is a rather critical/sensible part of the sim. \
:)</font></div> </div><div class="gmail_extra"><br><br><div class="gmail_quote">On \
Wed, Oct 30, 2013 at 11:44 AM, James Turner <span dir="ltr"><<a \
href="mailto:zakalawe@mac.com" target="_blank">zakalawe@mac.com</a>></span> \
wrote:<br> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px \
#ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><div \
class="im"><div>On 30 Oct 2013, at 10:33, Anton Gomez Alvedro <<a \
href="mailto:galvedro@gmail.com" target="_blank">galvedro@gmail.com</a>> \
wrote:</div> <br><blockquote type="cite"><div \
style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:normal;fo \
nt-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span style="font-family:arial,sans-serif;font-size:13px">I don't know! :D It \
looked like so after this short discussion: </span><a \
href="http://forum.flightgear.org/viewtopic.php?f=14&t=21020&start=30#p192454" \
target="_blank">http://forum.flightgear.org/viewtopic.php?f=14&t=21020&start=30#p192454</a></div>
<div style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:nor \
mal;font-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<br></div><div style="font-family:Helvetica;font-size:medium;font-style:normal;font-v \
ariant:normal;font-weight:normal;letter-spacing:normal;line-height:normal;text-align:- \
webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"> \
The comments in the code suggest a different concept however:<br></div><div \
style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:normal;fo \
nt-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<br></div><div style="font-family:Helvetica;font-size:medium;font-style:normal;font-v \
ariant:normal;font-weight:normal;letter-spacing:normal;line-height:normal;text-align:- \
webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"> \
<div>class FGGlobals {</div><div>...</div><div> // Number of milliseconds elapsed \
since the start of the program.<br></div><div> double \
sim_time_sec;</div><div><br></div><div>But the name given to the variable again \
suggests "simulated time in seconds", not milliseconds since start.</div> \
</div></blockquote><div><br></div></div><div>To be honest I wish we did not have \
those cumulative values - the comments are wrong, the property names are misleading. \
For 'real' dt (not simulated) we can of course offer elapsed seconds or msec \
since the program started, but I can't imagine many use cases where that's a \
genuinely interesting value.</div> <br><blockquote type="cite"><div \
style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:normal;fo \
nt-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<div>In practice, the variable doesn't grow when the simulator is paused, so the \
comment doesn't really hold, and it doesn't honour either speed-up nor warp \
settings, so it doesn't represent simulated time inside nor outside the aircraft. \
??? :D</div> </div></blockquote><div><br></div><div>No, but nothing anywhere says \
that it should represent either of those things (unless we have even more misleading \
comments or docs?)</div><div class="im"><br><blockquote type="cite"> <div \
style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:normal;fo \
nt-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
If it is not a bug, I guess we can agree that the context surrounding this property \
is, at least, confusing.</div></blockquote><div><br></div></div><div>Very \
likely.</div><div class="im"><br><blockquote type="cite"><div \
style="font-family:Helvetica;font-size:medium;font-style:normal;font-variant:normal;fo \
nt-weight:normal;letter-spacing:normal;line-height:normal;text-align:-webkit-auto;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
Personally, I tend to agree with James' explanation. It makes sense to me, \
assuming the ability to warp environment time independently of local aircraft time is \
a feature. How each system should interact with this concept, even how both timelines \
should interact to each other, I guess that requires careful thinking.</div> \
</blockquote><br></div></div><div>Note I figured out that explanation by reading the \
code and guessing, it's not based on anything 'official' \
:)</div><div><br></div><div>I tend to agree with what Torsten wrote - given that \
these are unphysical things we're doing, there are lots of differing use cases \
and any link between 'speed-up' and 'warp' is likely to be \
problematic. I do think including speed-up in sim-dt would be valuable, if it could \
be done safely, but I'd want to see a pretty convincing audit of Nasal/ and \
fgdata/Aircraft to establish how the value is being used and what kind of / quantity \
of bugs we might produce by making such a change.</div> <div><br></div><div>Kind \
regards,</div><div>James</div><div><br></div></div><br>------------------------------------------------------------------------------<br>
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<br></blockquote></div><br></div>
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developers love is also attractive to malware creators. Download this white
paper to learn more about secure code signing practices that can help keep
Android apps secure.
http://pubads.g.doubleclick.net/gampad/clk?id=65839951&iu=/4140/ostg.clktrk
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