Performance down with GLSL in QC

[lov]

Hello Guys,

i found an interesting issue with a QC composition of George Toledo. Renders well with 60fps in QC, but if add a Syphon Server for the comp, which has a client, the frame rate drops to 30 fps. How no idea why this happens, maybe an issue with GL state restore?

Here is the composition to test: http://dl.dropbox.com/u/2533/tons%20of%20spheres.qtz

[vade]

You must be using an old Syphon Server patch, or something. I am getting errors restoring the patch, looking for a resolution key.

Ensure you are using the latest Syphon QC ?

Either way, ill take a peek, but thats the first thing I noticed.

[vade]

I get 60 fps. This may just be a fill rate / GPU usage issue. That comp might be pushing you close to 1/60th a second, adding Syphon (a render to FBO phase for the screen size introduces more fill rate), maybe pushing you over the edge.

Does the FPS change with the size of your viewer changing?

[lov]

Using the latest public Syphon QC Plugin, not the SVN one. Should I try to build?

However, changing the size of the viewer (which also changes the rendering size) gives me change on the FPS. Around 512×384 is 60FPS, but changing a bit will drop to 30FPS without using Syphon too.

[vade]

Right, because its either a fill rate, or programmable pipeline issue using up the GPU cores. Adding additional operations are never “free”. Syphon tries its best to be as lightweight as possible, but sometimes a copy operation (and in the other client app, additional drawing) happens.

Alas, not much we can do about that. But it seems like that comp in and of itself is borderline too heavy for whatever you are running it on.

[lov]

Indeed. Thanks for the help as always, I should do more testing next time before posting about issues 🙂

[gtoledo3]

I’m kind of surprised to think of that shader program as being very intense.

On a non-Syphon note, try changing the depth parameter to something like 8~10 instead of the current. The lower that number, the less iterations of spheres will happen, and the fragment shader will tend to perform more quickly.

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