[Mesa-dev] GLSL 1.40 and fixed function

[Eric Anholt]

On Tue, 27 Mar 2012 10:41:09 -0700, Kenneth Graunke <kenneth at whitecape.org> wrote:
> On 03/27/2012 10:31 AM, Ian Romanick wrote:
> > On 03/26/2012 01:35 PM, Eric Anholt wrote:
> >> I've got a question for GLSL 1.40 that could use some interpretation:
> >>
> >> Section 1.2.5 in the spec says:
> >> "The following features, previously deprecated, are removed:
> >> ...
> >> Fixed functionality for a programmable stage. Supply shaders for
> >> all stages currently being used."
> >>
> >> What exactly does this mean? Undefined results? Link error? Draw
> >> time error? I couldn't find anything explicit in the 3.1 core spec
> >> (since it doesn't have fixed function, so it doesn't really explain
> >> interaction with it) or the compat spec (since it has
> >> ARB_compatibility, so that deprecated functionality is re-allowed).
> >
> > At the bottom of that list is also the line:
> >
> > "Removed features were recast under the ARB_compatibility
> > extension, within this specification."
> >
> > I believe this implies the same link error as in ES 2.0. The wording is
> > weird. I thought we ended up saying something more clear than this, but
> > it was a long time ago.
> >
> >> I think my resolution would be: Don't expose GLSL 1.40 outside of a GL
> >> 3.1+ core context, thus dodging the question of how to interact between
> >> the FF and GLSL 1.40 without GL_ARB_compatibility exposed.
> >
> > I think that's reasonable. Though, this may lead to people wanting
> > EXT_gpu_shader4 to get UBOs in some apps. I guess we can cross that
> > bridge when we come to it.
> >
> > There is also a requirement that shaders from different stage must have
> > the same version. We could just enable the same all-stages linker check
> > if any stage is 1.40 that we already have for ES shaders.
> >
> > It's not a huge deal to me either way.
> 
> Yeah, I think the linker needs to mandate all stages be present, like 
> ES.  That said, I'm still unclear what happens if you do a draw call 
> without a UseProgram.  Undefined results?  GL error?

Yeah, I haven't found any mandate there.  I would think a
GL_INVALID_OPERATION?

The link error makes sense, at least until
GL_ARB_separate_shader_objects.  And we just won't expose GL_EXT_sso on
a 3.1 core context.
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