Adrian,
Do you remember my suggestion that changing DataVariance might help ?
In certain threading modes osgUtil::Renderer uses 2 SceneViews to cull and
render 2 consecutive frames concurently. Robert used to call it
doublebuffering, first of these SceneViews culls and renders odd frames and
second culls and renders even frames. Technically its possible to have them
working concurently. For example first SceneView may be culling the graph
while second SceneView is outputing(drawing) RenderStage.
This shouldn't be done when some resources of the scene graph are shared and
they change with each frame. If some of these resources are used by both
SceneViews there might be race conditions - it will be possible that some of
them will be changed by first SceneView traversals while also being accessed
by second SceneViews traversals.
What it means for PSSM ? I bet that PSSM:cull changes some shared resources
(like Texgen or some Uniforms for example) in the same time as Draw in
Second View uses them. Classic race condition - sometimes cull wins
sometimes draw wins. Hence some flicker.
DataVariance set to DYNAMIC could be used to serialize SceneViews traversals
and may potentially solve your issue. The question is where in scene graph
this variance should be set. PSSM would be good place for this but I am not
sure if this is possible. Maybe Robert can suggest right place.
Cheers,
Wojtek
Thanks Robert,
no problem take your time for other new features. in the mean time i
will progress in PSSM as well...
regards adrian
2008/5/21, Robert Osfield <[EMAIL PROTECTED]>:
Hi Adrian,
I've got my head down dealing with some other complex areas of the OSG
right now - it's even a multi-threaded part... so I'm not in a good
place to dive into discussion about other complex areas. Give me a
week and I'll be a in better position.
Robert.
On Wed, May 21, 2008 at 8:01 AM, Adrian Egli OpenSceneGraph (3D)
<[EMAIL PROTECTED]> wrote:
Hi Robert, Hi others,
as you may get from the latest mailing list topics on Parallel Split
Shadow
Maps implementation and fixes, we get some flickering effect in the
shadow
if we are working in multi-threaded osgShadow.exe example. By add the
--SingleThread parameters, it works fine, no more flickering effect.
(some
one reported that they have to add also --screen 0, but this not the
same
problem, i guess) so back to the multi-threading issue we have in osg or
at
least in pssm.
i guess the problem comes from a bad synchronisation or may we don't
have
yet a the camera synchronised or describted in a dependencie graph.
because in pssm we render (a-c) shadow maps into RTT and then we render
the
whole scene as
default viewing camera master m. the a-c should be finish before we
start
to
render the visible / master camera. because the shadow maps are view
depended to the m.
what are we doing:
cull , update all pssm shadow map cameras, render/draw the shadow map
cameras, render the scene with GLSL based on the shadow map texture.
how can we synchronise this step, it seams not to be enought to work
with
render order prerender nestedrender or postrender.
thanks for short describtion how it works in osg, and how we should fix
the
problem we have.
well for the moment we have a robust working PSSM for singlethread, and
this
isn't so bad, but it should also work for other settings.
regards
adrian
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