[osg-users] performance issues with RTT

Robert Osfield robert.osfield at gmail.com
Fri Sep 5 12:51:54 PDT 2008


HI Guys,

What are you all doing with your RTT Camera's?  Are you just doing
render to texture, or are you doing a copy to Image/glReadPixels as
well?   The later will throw a big slow down as it requires a round
trip to the graphics card and an associated finish of the all OpenGL
prior to the glReadPixels.

Robert.

On Fri, Sep 5, 2008 at 6:38 PM, Harash Sharma <harashsharma at yahoo.com> wrote:
> Hi Steffen, Guay and Robert,
>
>    In the same regard I would like to mention something. We have also
> developed an application that uses multiple RTT cameras. However only one
> camera is active at a time ( the rest are masked using node mask). All
> cameras differ only in the resolution of the texture, they are viewing
> exactly the same scene and have identical fields of view. We too have found
> that the frame rate has a lot of dependence on the texture size. 256 x256
> texture gives a fairly high frame rate(30+ frames/second), 512x512 slows it
> down considerably (to around 8 frames / second) and 1024x1024 slows it even
> further (~ 1 fps). All these figures are in release mode build.
>
> My machine specifications
> Processor:     Xeon 5160
> RAM:            4 GB Fully Buffered DDR2
> Graphics:        nVidia Quadro FX4500 (512MB)
>
>     I would be highly obliged if a way out can be suggested.
>
> Regards
>
> Harash
> ----- Original Message ----
> From: Steffen Kim <mailto.stk at web.de>
> To: osg-users at lists.openscenegraph.org
> Sent: Friday, September 5, 2008 10:04:25 PM
> Subject: Re: [osg-users] performance issues with RTT
>
> Thanks for the hints so far...
>
> I gave you wrong information since I forgot that I take care of the
> NPOT-stuff myself.
> The API I use later on needs POT-textures so I make sure that only
> POT-textures are rendered. So in fact my textures are normally 2048x1024.
>
> I know that the performance issues are most certain a problem of the texture
> rendering since we have parts of the application where even huger amounts of
> (normal render-to-view) cameras are involved without slowing down everything
> as much. The scene is pretty simple too and runs smoothly without the
> RTT-cameras.
> Back on Monday I will try to get some FPS-values for exactly the same
> camera-setup with and without RTT for different scene complexities (here in
> Germany the weekend begins now ;)).
>
> What I just found out is that the texture sizes make a huge difference in
> rendering performance. With 256x256-textures my cameras hardly slow down the
> viewer at all. That's also an evidence that the problem has to be somewhere
> in the texture-creation-part.
> If this cannot be enhanced then I probably have to find a good balance
> between quality and speed.
> But I still have hopes that there are better ways to improve my performance
> without having to sacrifice too much resolution-wise.
>
> BTW: I'm running my stuff on a Xeon 5160 at 3GHz and 2GB RAM with a Radeon
> X1900 card.
>
> Have a nice weekend,
> Steffen
>
>
>
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