[osg-users] [Toward DrawElementBaseVertex as drawcall]

[Julien Valentin]

up 
(in order my post edits appear on the ML)


mp3butcher wrote:
> Hello Robert,
> I achieve a basevertex example and debug with nvidia gl debugger.
> https://github.com/mp3butcher/OpenSceneGraph/tree/master/examples/osgSharedVAO
> It appears that glBindVertexArrayObject seams to have a cost 500ns !? when  big bufferobjects are involved in the vas
> Sure bos are remapped at each call...
> 
> I added a check not to call glBindVertexArrayObject when currentvaobound doesn't change and achieve the same perf as my rejected submission (a near 0 draw submission overhead ) 
> 
> Code:
> void VertexArrayState::bindVertexArrayObject() const {
>     if(_state->getCurrentBoundVAO()!=_vertexArrayObject){
>         _state->setCurrentBoundVAO(_vertexArrayObject);
>         _ext->glBindVertexArray (_vertexArrayObject);
>     }
>  }
> 
> void VertexArrayState::unbindVertexArrayObject() const {
>     no overhead here if(_state->getCurrentBoundVAO()!=0){
>          _state->setCurrentBoundVAO(0);
>          _ext->glBindVertexArray (0);
>     }
>  }
> ////and inlined mutable property get/setBoundVAO in osg/State
> 
> 
> 
> It's not very elegant but it do the job.
> 
> Bench with a DrawArrays low res sparse buildings scene:
> (on a  NVGTX660OC)
> 1VAO/Geom: DrawCost 4
> shared VAOs: DrawCost 2 
> 
> Bench with a DrawElementShort BigCity scene:
> https://drive.google.com/file/d/0BxIH-jcsgYDdTG5ha21HZE1jX1E/view
> 1VAO/Geom: DrawCost 9
> shared VAOs: DrawCost 4 
> 
> 
> Any toughts about it?
> 
> Cheers
> 
> 
> robertosfield wrote:
> > Hi Julien,
> > 
> > On 6 February 2017 at 10:33, Julien Valentin <> wrote:
> > 
> > > I remember your rejection, but it's not what I asked.
> > > I would like your sentiment about what the book extract says about efficient draw submission and basevertex based drawcall....
> > > 
> > 
> > Personally I have plenty of more pressing things to work on the OSG
> > than chase after a possible small benefit.  For OSG-3.6 my focus will
> > be completing my work on fixed function -> shader pipeline and fixing
> > bugs.
> > 
> > Please remember these potential gains are in the wider context of real
> > application with a wider range of different potential bottlenecks,
> > typically the CPU and GPU bottlenecks be such that you may not see
> > expected benefits.
> > 
> > The right way to optimize graphics applications is benchmark test
> > cases that most closely follow the needs that your
> > application/OS/hardware with require when dealing with real datasets.
> > Narrow benchmarks won't typically reveal what bottlenecks the full
> > application and full data will see so you have to be very careful
> > about extrapolating possible bottlenecks.  With the full application
> > and data tests you get a real picture of the what are the biggest
> > bottlenecks and these are ones that you will see the most benefit from
> > optimizing.
> > 
> > Given this context I would be sceptical about how much value will see
> > in sharing VAO and using base vertex.  With anything that adds
> > complexity to the API and implementation you need to make sure there
> > is real value in added them to justify this complexity.
> > 
> > Robert.
> > _______________________________________________
> > osg-users mailing list
> > 
> > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> > 
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