[osg-users] PrimitiveSets and performance

Robert Osfield robert.osfield at gmail.com
Fri Dec 2 09:36:56 PST 2016

Hi Riccardo,

I'm a surprised you saw a significant change in performance, in
particular for the worse, this suggest that the merging has some kind
of error in it or the driver isn't handling the larger sized
primitives efficiently for some reason.

One thing of note is that both the draw dispatch and the draw GPU are
around the same amount slower in the merged case, this suggest that
the something in happening in the driver/GPU combination that is
blocking the OpenGL FIFO and then in turn blocking the OSG draw
dispatch that is putting data into the OpenGL FIFO.

There isn't any way for us to pinpoint what this might be with the
details given.

Check for GL errors being printed to the console.  Also try writing a
your scene graph out to a .osgt  before and after the merge so you can
QA the merge by hand - do this for a subset of your whole scene graph
as reviewing a really big dataset will be really heavy on an editor.


On 2 December 2016 at 15:32, Riccardo Corsi <riccardo.corsi at kairos3d.it> wrote:
> Hi all,
> I'm trying to find out the best geometries and primitive sets layout on a
> model that I'm using as performance benchmark.
> The model is quite heavy in terms of vertices and polygons, and everything
> is rendered at the moment with DrawArrays.
> In the attempt to reduce the draw calls, I've recombined the primitive sets
> contained in every geometry into a single primitive set.
> I expected draw/gpu time to improve, and I've found the exact opposite -
> find attached the 2 screenshots with the stats (before and after primitives
> merge).
> After merging the primitive sets I've also tried to force VBO usage instead
> of display lists, which improve things slightly, but always far worse than
> before merging.
> Can anyone comment on this result?
> Thank you,
> Riccardo
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