Yes, your are correct it you run a single instance of fg with three displays
with whichever scheme you use; e.g. using the XML file to create a left,
center, and right camera for the scene or one of the video splitters to break a
single large camera into three channels for each display.
However, if you run an instance of fg using, for example, the center as the
master FDM, then create two "slave" fg's using the FDM=NULL option for each
left and right instance each instance starts with a different random seed. This
occurs whether you run all three instances on a single CPU or, as in our case,
each instance on a single core of a multi-core machine since each instance
creates it's own scene graph. The advantage of the multi-core machine is
performance limited only by the bandwidth of the busses and graphics pipelines
and GPUs. have not really drilled down just where or what are the limiting
factors using a multi-core machine with multiple video cards; just know it is
faster based on fps for each core versus running everything on a single core
machine. The disadvantage is many of the dynamic features like clouds, AI
traffic, etc are not sync'd across processes.
Jan Comans solved the problem by using a *fixed* random seed ( another oxymoron
;-) ) for the 3d clouds at least.
Another approach, perhaps a bit more complicated to make it cross-platform
compatible, would be to use shared memory to have one 3d cloud generator as the
master and the slaves would simply read the data from shared memory.
BTW the warping code will run in a single core machine with multiple displays
and the performance hit is minimal.
John
----- Original Message -----
From: "Stuart Buchanan" <stuar...@gmail.com>
To: "FlightGear developers discussions"
<flightgear-devel@lists.sourceforge.net>
Sent: Thursday, November 8, 2012 3:24:37 PM
Subject: [Flightgear-devel] 3d clouds on multi-display systems (was Re:
FSWeekend 2012...)
On Wed, Nov 7, 2012 at 5:03 PM, John wrote:
> second, we also run fgfs on a multi-core machine with three graphics cards.
> Performance is around 50-60 fps for each core. and thanks to Jan Comans the
> 3d clouds are sync aross all three displays.
Hi John,
I'm confused. From my reading of Durk's post, 3D clouds would appear to work
fine for a multi-display system "out-of-the-box", but your comment
here indicates
that there is an issue that requires fixing by restricting the random seed.
Can you explain a bit more about how you are running FG in this instance?
In particular are you running multiple instances of the simulator?
I _should_ be the case that if you're running multiple cameras on a single
scene-graph, the existing code will Just Work. However I've not got the
option to test this myself.
-Stuart
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