On 12/03/2015 09:03 AM, Timothy Arceri wrote:
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.
Right, I think it's there only for uniforms. Uniforms will get
sequential locations for structure items. Now I can't find test for this
but I remember writing the code for 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.
True, I missed this bit. I guess it would be good to make a search in
Khronos bugzilla if there is any discussion about this topic. I don't
see much reason to require name to match if location, type and other
required qualifiers match but it does seem to be required :/
Tim
[1]
http://cgit.freedesktop.org/piglit/commit/?id=f1e416b8e65ad95c6ce9e
04a80d83e7f9e1e9239
[2]
http://cgit.freedesktop.org/piglit/commit/?id=2b2bb62ce03ffa065e9b5
91cd
05e12c623ed4759
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