Howto:Activate multi core and multi GPU support
FlightGear supports a number of different threading modes to make use of multiple CPUs or GPUs, this applies mostly to high-end multi-core or multi-GPU, multi-screen (or multi-window) setups and may improve performance (see Howto: Configure camera view windows).
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Proposals & RFCs
Selecting threading modes
| Note Beginning with FlightGear 3.0, you should be careful when changing the default OSG threading settings, as enabling multi-threading seems to be an increasingly reliable way to trigger race conditions/segfaults (crashes). Also see ticket 1393 and 
There is a property supported named /sim/rendering/multithreading-mode this can be set either in the preferences.xml file located in the flightgear data folder (base package: $FG_ROOT) or by using the --prop:/sim/rendering/multithreading-mode=... parameter from the console (or fgrun) this affects directly the osgviewer threading mode, supported values are:
* AutomaticSelection * CullDrawThreadPerContext * DrawThreadPerContext * CullThreadPerCameraDrawThreadPerContext
Further information on threading modes can be found here: http://firstname.lastname@example.org/msg09620.html and here: http://email@example.com/msg09611.html
To set this in a separate XML file, just include it from preferences.xml (toplevel PropertyList node):
<?xml version="1.0"?> <PropertyList> <sim> <rendering> <multithreading-mode>AutomaticSelection</multithreading-mode> </rendering> </sim> </PropertyList>
This property must be set during initialization, modifying it at runtime has no effect.
Multithreading modes allocate two instances of OpenGL resources to speed up rendering . Default implicit buffer attachment policy adds depth buffer to FBOs if only color buffer was attached.
if you have a single graphics card, having a thread per camera (each one with a graphics context) doesn't necessarily improve the performance, what is more, it can degrade it. The reason is that each thread will be competing for the graphics card, which is an exclusive resource, and the driver is forced to perform many context switchs. If you are using multiple graphics contexts then by default the OSG/OpenGL will be creating OpenGL objects (like textures) on a per context basis. So one osg::Texture in the scene graph even if it's rendered on two contexts you'll have two separate TextureObjects/OpenGL texture objects.