[Mesa-dev] Shader Interface Matching

[Timothy Arceri]

On Thu, 2015-12-03 at 08:46 +0200, Tapani Pälli wrote:
> 
> On 12/03/2015 05:58 AM, Timothy Arceri wrote:
> > Hi All,
> > 
> > I recently pushed a couple of piglit tests [1] and [2] that test
> > for
> > matching of blocks and structs based on location rather than name
> > when
> > an explicit location is given.
> > 
> > The test pass on Nvidia but fail in current Mesa.
> > 
> > However I just came across this in section 7.4.1 (Shader Interface
> > Matching) the OpenGL 4.5 spec:
> > 
> >     "- An output block is considered to match an input block in
> >        the subsequent shader if the two blocks have the same block
> >        name, and the members of the block match exactly in name,
> >        type, qualification, and declaration order.
> >      - An output variable is considered to match an input variable
> >        in the subsequentshader if:
> >        -- the two variables match in name, type, and qualification;
> > or
> >        -- the two variables are declared with the same location and
> >           component layout qualifiers and match in type and
> >           qualification."
> > 
> > But then later it says:
> > 
> > "The inputs and outputs on an interface between programs need not
> > match
> > ex-actly when input and output location qualifiers (sections
> > 4.4.1(“Input Layout Qual-ifiers”) and 4.4.2(“Output Layout
> > Qualifiers”)
> > of the OpenGL Shading LanguageSpecification) are used. When using
> > location qualifiers, any input with an inputlocation qualifier will
> > be
> > well-defined as long as the other program writes to amatching
> > output,
> > as described above. The names of variables need not match when
> > matching
> > by location."
> > 
> > So my question is why bother to inforce name matching on blocks
> > when
> > not using SSO? Should I folow the spec or do what Nvidia does?
> 
> I was reading through these sections when looking at the tests. My 
> understanding is that Mesa is too strict currently since matching by 
> location is defined as above, this change came in 4.3 spec.

Mesa also has a bigger problem in that it parses the location from
structs and interface blocks but doesn't actually use it.

>  I don't see 
> it being limited to SSO scope. How I understand is that this
> paragraph 
> belongs to generic scope of "Shader Interface Matching" section.

But doesn't the end of the first line "between programs" mean its only
talking about SSO. At the top when it talks about names being required
to match for blocks and block members it talks about the interface
between shaders rather than programs.

> 
> 
> > Tim
> > 
> > 
> > [1] 
> > http://cgit.freedesktop.org/piglit/commit/?id=f1e416b8e65ad95c6ce9e
> > 04a80d83e7f9e1e9239
> > [2]
> > http://cgit.freedesktop.org/piglit/commit/?id=2b2bb62ce03ffa065e9b5
> > 91cd
> > 05e12c623ed4759
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
> > 
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