[Mesa-dev] GLSL 1.40 and fixed function

[Kenneth Graunke]

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?