[Interest] [qt3d] Few questions about shader management with custom materials

[Xavier Bigand]

2016-06-21 14:49 GMT+02:00 Sean Harmer <sean.harmer at kdab.com>:

> On Tuesday 21 June 2016 14:40:37 Xavier Bigand wrote:
> > I have few more questions :
> >  - How Qt know the type of the uniform, does it parse the shader source?
>
> We don't parse the source but rather use the introspection API to extract
> uniform types, locations and other properties (needed for building UBOs).
>


Nice, I didn't know that there is a such API, in our engine types are
hard-coded.


>
> >  - How from the material class I can retrieve the model view projection
> > matrix to update the corresponding uniform of the vertex shader? Maybe
> > there is a signal that notify the material when the transform of the
> parent
> > object changed?
>
> No need. Qt 3D automatically sets some uniforms. I don't know if these are
> documented yet but take a look at:
>
>
> http://code.qt.io/cgit/qt/qt3d.git/tree/src/render/backend/renderview.cpp?h=5.7#n141
>
> for the full list. So to get the model view projection compound matrix you
> can
> just declare a uniform mat4 mvp; or uniform mat4 modelViewProjection; in
> your
> shader and it will be set automatically for you.
>
> At some point we may add some API to allow you to populate your own
> uniforms
> with such calculated values. For now, use the names in the above link.
>


I just saw it and you would prefer to avoid patching our shader code
because we are still fixing our current engine and I need to be able to
merge everything on my qt3d branch.
But I can certainly do it if it concern only vertex shaders.


>
> >  - Our shaders works on all platforms (opengles/opengl), In this case
> can I
> > remove the Technique or the graphicApiFilter to be sure that the same
> code
> > runs everywhere?
>
> You need at least one Technique. I *think* that if you don't specify a
> graphics api filter it will select it - but you'll need to play to confirm.
> Otherwise, just create a wrapper around Technique and instantiate it for
> both
> GL and GL ES api filters.
>

I'll try.


>
> >  - Does qt3d use glsloptimizer on some platforms?
>
> No. We don't do any "tinkering" with shader sources other than what
> QOpenGLShaderProgram does (for ensuring highp etc are defined). Oh, the
> only
> other thing we do is an include pragma. We use this for including the
> common
> lighting code.
>
> Cheers,
>
> Sean
>
> >
> > 2016-06-21 11:26 GMT+02:00 Sean Harmer <sean.harmer at kdab.com>:
> > > On Tuesday 21 June 2016 00:03:31 Xavier Bigand wrote:
> > > > Thank you, it's super nice.
> > > >
> > > > Does qt3d cache the compilation of shaders between two executions of
> the
> > > > application?
> > >
> > > Not yet. :)
> > >
> > > Sean
> > >
> > > > 2016-06-20 22:54 GMT+02:00 Sean Harmer <sean.harmer at kdab.com>:
> > > > > Hi,
> > > > >
> > > > > On 20/06/2016 17:17, Xavier Bigand wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > I am planning to use our custom materials with Qt3D, because will
> > >
> > > already
> > >
> > > > > have an uber shader for the lighting and shadowing of objects.
> > > > > I think that I'll create one material called LightingMaterial that
> can
> > > > > change the shader's sources depending of his properties, but in
> this
> > >
> > > case
> > >
> > > > > it seems that I'll instanciate too much shader programs.
> > > > > Are shaderprograms automatically managed in sense of I can
> instanciate
> > > > > many program with the same code?
> > > > >
> > > > >
> > > > > Yes, the OpenGL shader programs are cached and hashed by the
> renderer.
> > > > >
> > > > > Cheers,
> > > > >
> > > > > Sean
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Xavier
> > > > >
> > > > >
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> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
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> > > --
> > > Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
> > > KDAB (UK) Ltd, a KDAB Group company
> > > Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
> > > Mobile: +44 (0)7545 140604
> > > KDAB - Qt Experts
>
> --
> Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
> KDAB (UK) Ltd, a KDAB Group company
> Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
> Mobile: +44 (0)7545 140604
> KDAB - Qt Experts
>



-- 
Xavier
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