[Mesa-dev] glsl: should uniform initializers be allowed in GLSL ES 3.00?

[Matt Turner]

On Wed, May 14, 2014 at 10:00 AM, Aras Pranckevicius <aras at unity3d.com> wrote:
> Hi,
>
> Mesa's ast_to_hir.cpp does a check like:
>
>   state->check_version(120, 0, &initializer_loc,
>                            "cannot initialize uniforms");
>
> i.e. it does not allow uniform initializers on GLSL ES 3.00.
>
> Upon my reading of the spec, I can't find any place where that would be
> disallowed. ES 3.00 seems to be based on GLSL 3.3, with a bunch of stuff
> removed and added. Uniform initializers aren't listed in the "removed"
> section (spec 3.00.4, section 1.1.4). So maybe the check should be changed
> to allow 300 in the ES min version?

The GLSL 3.30 spec says

> All uniform variables are read-only and are initialized externally either at link time or through the API. The link time initial value is either the value of the variable's initializer, if present, or 0 if no initializer is present. Sampler types cannot have initializers.

While the GLSL ES 3.00 (.4) spec says (The GLSL ES 3.1 spec contains
this wording too)

> All uniform variables are read-only. They are initialized to 0 at link time and may be updated through the API.

So I think we're correct in disallowing it.

Chalk it up to another trivial divergence of ES in unexpected way.

Ian, does it seem like we can make a really trivial extension that
gives you back the wording in the Desktop GLSL spec? Are there other
interactions we need to think about? There's already wording
explicitly disallowing initializing samplers in a shader.