[Mesa-dev] [PATCH 1/2] i965: Make the precompile ignore DEPTH_TEXTURE_MODE on Gen7.5+.

[Ian Romanick]

On 01/01/2015 10:51 PM, Kenneth Graunke wrote:
> On Thursday, January 01, 2015 10:21:43 PM Ian Romanick wrote:
>> On 12/31/2014 08:04 PM, Kenneth Graunke wrote:
>>> Gen7.5+ platforms that support the "Shader Channel Select" feature leave
>>> key->tex.swizzles[i] as SWIZZLE_NOOP except when GL_DEPTH_TEXTURE_MODE
>>> is GL_ALPHA (which is really uncommon).  So, the precompile should leave
>>> them as SWIZZLE_NOOP (aka SWIZZLE_XYZW) as well.
>>>
>>> We didn't notice this because prog->ShadowSamplers is not set correctly.
>>> The next patch will fix that problem.
>>
>> I had some patches related to this a long time ago, but I'm not sure
>> what happened to them.  My recollection is that, basically, nothing
>> should use prog->ShadowSamplers.  That was only used by the
>> ARB_fragment_program assembler, and other paths (including ff fragment
>> programs) don't set these fields.  I just pushed the (ancient!) branch
>> to my fd.o repo as r300-shadow-samplers.  The two patches are from 2011. :(
> 
> No, it's definitely set.
> 
> link_uniforms.cpp sets shader->shadow_samplers, which ir_to_mesa copies
> to prog->ShadowSamplers.  I'm guessing we stopped copying that at some point.
> 
> I don't see why we shouldn't use it...

The commit message from one of those patches explains it:

commit 6498addabe8fcb8a96064ecdd15b6438b66e1089
Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Mon Nov 14 21:33:27 2011 -0800

    r300g: Use rc_sub_instruction::TexShadow, not gl_program::ShadowSamplers
    
    gl_program::ShadowSamplers has two possible meanings.  For
    ARB_fragment_program, it tells which texture units have been used with
    shadow comparisons (e.g., the SHADOW2D texture target).  The flags are
    used by the assembler to generate errors when programs use the same
    texture unit for both shadow and non-shadow look-ups.
    
    For a GLSL program, it tells which *abstract* GLSL sampler uniforms
    were declared as a shadow sampler type (e.g., sampler1DShadow).  In
    GLSL, sampler indices do *NOT* correspond to texture units (as they do
    in ARB_fragment_program).  By calling glUniform1i, an application can
    bind texture unit 3 to sampler 7.
    
    At this point in code generation, we may want to know if texture unit
    3 has shadow comparisons enabled or if sampler 7 was a shadow sampler.
    The old code determined if texture unit 3 has shadow comparisons
    enabled or if sampler 3 was a shadow sampler.  This is clearly wrong.
    
    Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
    Cc: Tom Stellard <tstellar at gmail.com>
    Cc: Marek Olšák <maraeo at gmail.com>
    Cc: Alex Deucher <alexander.deucher at amd.com>

Long story short, from the next commit message, "The only places that
really need this data are at fairly high levels in the GLSL compiler or
the ARB_fragment_program assembler.  Every place else really wants some
other field."

At the time I wrote that code, r300 was the only driver using
gl_program::ShadowSamplers.  It looks like i965 started using it about
a year later.  Either the meaning of that field has changed, my
understanding of it is completely wrong, or we shouldn't use it either.

> --Ken


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