Hi Tugkan,
Robert mentioned lengthy read operation. It may be related to read buffer
operation thats used to compute shadow volume in
LightSpacePerpspectiveShadowMapDB. If your slave view uses
osgShadow::LightSpacePerpspectiveShadowMapDB then you may check if
osgShadow::LightSpacePerpspectiveShadowMapCB (cull bounds flavour) has the
same problem.
I am aware of LightSpacePerpspectiveShadowMapDB glReadBuffer limitation but
I could not find quick and easy to implement workaround that would do this
without scanning the image by CPU. I allocate small 64x64 texture and render
the scene there, then read it into CPU memory and use CPU to scan pixels to
optimzie shadow volume from depths and pixel locations strored in this
prerender image.
Wojtek
----- Original Message -----
From: "Robert Osfield" <[email protected]>
To: "OpenSceneGraph Users" <[email protected]>
Sent: Wednesday, January 13, 2010 1:04 PM
Subject: Re: [osg-users] RTT slave views and multi-threading
Hi Tugkan,
The osgdistortion example works a bit like what you are describing,
could you try this to see what performance it's getting.
As for general notes about threading, if you are working on the same
graphics context as you are then all the draw dispatch and the draw
GPU can only be done by a single graphics thread so there is little
opportunity to make it more parallel without using another graphics
card/graphics context and interleaving of frames.
As for why the second camera is very expensive on draw dispatch, this
suggest to me that it's blocking either due to the OpenGL fifo being
full or that it contains a GL read back operation of some kind.
Robert.
On Wed, Jan 13, 2010 at 11:34 AM, Tugkan Calapoglu <[email protected]> wrote:
Hi All,
I am using a slave view for rendering the scene to a texture. Initially
I tried with a camera node, however, this did not work well due to a
problem in LiSPSM shadows and I was suggested to use RTT slave views.
My setup is as follows: There is a single main view and I attach a slave
view to it. This slave view is attached with addSlave( slave , false );
so that it does *not* automatically use the master scene.
I attach a texture to the slave view and make my scene child of this
view. I attach a screen aligned quad to the main view. This quad
visualizes the RTT texture from the slave view.
Now I have a threading problem which can be seen on the snapshot I
attached. There are two issues:
1- The main view (cam1) has a very large draw time even though it only
renders the screen aligned quad. I double checked to see whether it also
renders the actual scene but this is not the case.
2- Slave view does not run cull and draw in parallel. Cull and draw do
run in parallel if they are not rendered with the slave view. Moreover,
if I change the render order of the slave camera from PRE_RENDER to
POST_RENDER it is ok.
I could simply use POST_RENDER but I am afraid it introduces an extra
one frame latency. If I render the screen aligned quad first and the
scene later than what I see on the quad is the texture from previous
frame (right?).
Any ideas?
cheers,
tugkan
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