Re: [Flightgear-devel] Syncing sim time

[Jan C. <jan...@co...>]

Hi all,

I got an email from Jack drawing my attention to this topic. I have been
out of the loop for a while, apparently a PhD thesis doesn't finish itself.
Of course my fingers started twitching after Jacks' email, so I pulled in
the latest git and tried a couple of things. I noticed the update to the
cloud code using a dedicated rng seeded with the time block. On my systems
this seems to work, in principle this is the same as the patch I used a
while ago (which is in a custom FG repo: https://gitorious.org/csflightgear)
the only difference I spot is that my patch also touched cloud code in
Simgear. I didn't dive deep enough into the code to see if the simgear
cloud code is still used, so I don't know if this is why Vivian is not
having the correct results.

If I remember correctly, there were two reasons to use a fixed seed. First,
in the simulators we are using, there is no guarantee that the system
clocks are in sync at all times. Yes they are running ntp, but still there
is no guarantee nobody tinkers with a machine in such a way that the clock
gets changed.
The second, and more important reason, is to be able to run with exectly
the same cloud field in different runs. Depending on the kind of experiment
we are running, it can be useful or even necessary to present each subject
with the same cloud field.
Having said this, I think the current patches (either mine or the time
slice one) are only temporary fixes. In my opinion, the randomness should
end up in the property tree in some way. This should enable us to
communicate it to different FG instances, be it on the same machine or
across the network. This would not only help multi-screen/multi-machine
setups, but would also benefit multi-player scenarios. Nothing is worse
than diving into a cloud for cover in a dogfight with the other guy not
having a cloud to obscure his view :)

Enough ranting for now, as soon as I find some more time, I'm going to look
at this a bit more.

Cheers,
Jan


On Fri, May 10, 2013 at 5:58 PM, <cas...@co...> wrote:

> Hi,
>
> Sent Stuart a set of diff files provided by Jan.
>
> If you would like copies, just holler.
>
> Jack
>
> ----- Original Message -----
> Stuart
>
> provides for
>
> on
>
> a
>
> You did indeed add some code - and I have tested it here on 2 machines and
> on 2 instances on one machine. It doesn't seem to do what you intended.
> https://dl.dropboxusercontent.com/u/57645542/clouds.png
> I ensured that the 3D cloud settings were the same, using the same live
> data. Do I need to do anything else?
> Vivian
>
>
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