Hi, Robert,
Thanks for the explanation. I'm still trying to make sense of
the mechanism used for threading. I'll say I'm a bit overwhelmed.
Looks for sure I'll need to set the option of BeforeSwapBuffers
for the barrier operation for the viewer, which is not the default.
More tinkering ahead!
Best Regards,
Yefei
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Robert Osfield
Sent: Thursday, January 21, 2010 12:27 PM
To: OpenSceneGraph Users
Subject: Re: [osg-users] Separating draw and swapbuffers
Hi Yefei,
The set up of threading on various graphics contexts that the viewer
is managing is set up in the src/osgViewer/ViewerBase.cpp's
ViewerBase::startThreading() method. In this code there is two parts
of interest to management of the swap of the graphics contexts.
First up a bit of background - when multithreading each
GraphicsContext has a GraphicsThread, and each GraphicsThread has an
OperationQueue that contains all the operations to run for that
context. The operations to run are set up the
Viewer::startThreading() by adding them to the OperationQueue. The
key operations added are first the a RunOperation() that dispatches
all the rendering of all the cameras attached to the GraphicsContext,
then there is a BarrierOperation that is to added after the rendering
dispatch to synchronize threads before, then finally the
SwapBufferOperation. There is also an option for moving this barrier
to after the swap buffer.
In you case it sounds like you would like to introduce your own
BarrerOperation to do you own syncronization of threads.
Unfortunately right now osgViewer hides this in the startThreading()
method, but potentially we could tweak he ViewerBase API to allow you
to get/set the BarrierOperation, as well as the SwapBufferOperation.
There might be a bit of complication in that right now the
BarrierOperation has to be constructed with the correct number of
threads, which is only 100% known once you're inside the startThread()
method, so perhaps a BarrierOperation callback would suffice.
Robert.
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