[osg-users] Serialize bufferobject configuration of BufferData

Julien Valentin julienvalentin51 at gmail.com
Thu Mar 30 03:20:37 PDT 2017

I totally understand your prorities (further it's release time:/) and your position on VASSharing...
(I began coding VAS-that i think you refer to VertexArrayBlock- and perContextVAS to do so)
I will not bother you until it's not (too) controversal...

But i'm not agree with you calling basevertex drawcall a hack.. 
The sacrosaint 0 draw overhead is not hacking, it's the (unreachable) absolute that drove the GL evolution this 20 last years!? ( if basevertex is hacking, what about indirectdraw? lol)

I would be glad to help you with the shader_pipeline branch but I'm afraid not to have a view of osg macro enough to help in anyway:/


robertosfield wrote:
> Hi Julian,
> I don't have the time right now to dive in to a complex discussion.  A
> few general feelings on the topic so you know where I stand:
> First up sharing VAO's would be best done by shading a
> VertexArrayBlock container class for per vertex arrays, that
> osg::Geomertry objects would share.  The VertexArrayBlock would map to
> VAO's.  At this point in time I don't think the performance benefit of
> adding this extra level of complexity into the OSG is probably not
> justified - in tests I did with your early VAO sharing code
> performance was worse than the non shader VAO implementation that is
> now in the core OSG.  You may have improved your VAO sharing
> implementation to avoid the CPU overhead that was limiting
> performance, but I wouldn't expect it'll make a big difference for
> most OSG usage cases.
> The BaseVertex extension to OpenGL is something that looks like a hack
> for lazy OpenGL application developers that don't wish to update their
> index and draw array offsets.  The osg::PrimitiveSet class has an
> ofsetIndices(int) method makes it easy to readjust primitive sets when
> vertex array are merged, so it's essentially the same feature, just
> implemented on the OSG side and in a way that is compatible with all
> OpenGL versions and compatible with scene graph code that traverses
> the scene graph for things like intersection tests.  I am not aware of
> any real benefit of base vertex for OSG users.
> We are now not far from making the next stable OSG release, I still
> have shader_pipeline functionality to complete for it, this is my
> focus.  The shader_pipeline functionality will benefit the majority of
> OSG users so in terms of bang for the buck this is where I need to
> spend my time working on rather on niche areas of the OSG/OpenGL
> usage.
> Are there are small and uncontroversial changes to the OSG that will
> help your usage case then please put them forward.
> Robert.
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