[Piglit] [PATCH 10/29] glapi: Read list of core extensions

[Eric Anholt]

On Fri, 25 May 2012 15:20:14 -0700, Chad Versace <chad.versace at linux.intel.com> wrote:
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> On 05/25/2012 09:19 AM, Paul Berry wrote:
> > On 21 May 2012 11:08, Pauli Nieminen <pauli.nieminen at linux.intel.com <mailto:pauli.nieminen at linux.intel.com>> wrote:
> > 
> >     There is extensions that have been pulled as is into core. Those
> >     extensions only declare extension functions in gl.spec. To allow stub
> >     loader know that required function is supported because of GL version we
> >     need to add core version to the extension functions.
> > 
> > 
> > Can you explain in more detail why this is necessary?  I thought that when an extension is pulled into core, the implementation was required to list that extension in its extension string.  So the stub loader should already know that these functions are supported.
> 
> The spec states that implementations are required to
> continue advertising the extension string after it becomes
> core. From the OpenGL 3.2 (Core Profile) spec, Section I.3.2:
> 
>   ARB extensions can be promoted to required core features in later revisions of
>   OpenGL. When this occurs, the extension specifications are merged into the core
>   specification. Functions and enumerants that are part of such promoted extensions
>   will have the ARB affix removed.
> 
>   GL implementations of such later revisions should continue to export the name
>   strings of promoted extensions in the EXTENSIONS strings and continue to support
>   the ARB-affixed versions of functions and enumerants as a transition aid.
> 
> I don't know, though, how consistently drivers adhere to this
> requirement.

I think the quoted "should" does not mean "must".

I think nvidia didn't advertise core-merged extensions for >3.0.  This
spec quote also just doesn't make sense to me, since for example
GL_ARB_texture_buffer_object requires things that aren't part of what
was merged into core, despite it being in the list of things promoted to
core.

I would propose that we also don't advertise merged-to-core extensions
in our 3.1+ core versions.  Given that the user is explictly asking for
a bumped GL version, this "transition aid" is not really buying them
anything.
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