[Mesa-dev] [PATCH] st/mesa: apply DepthMode swizzle to stencil texturing as well

[Ilia Mirkin]

On Wed, Feb 17, 2016 at 11:13 AM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 17.02.2016 um 14:43 schrieb Ilia Mirkin:
>> Gallium doesn't present these as GL_RED-style. A swizzle is necessary to
>> present the proper data in the unused components.
>>
>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>> ---
>>
>> The GL 4.5 compat spec also makes it clear that sampling from stencil is the
>> same as sampling from depth (except obviously the stencil value is used). So
>> the same swizzling rules should apply.
>>
>> However I'm unaware that this fixes anything in particular.
>>
>>  src/mesa/state_tracker/st_atom_texture.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/src/mesa/state_tracker/st_atom_texture.c b/src/mesa/state_tracker/st_atom_texture.c
>> index f59eeec..4b7ad77 100644
>> --- a/src/mesa/state_tracker/st_atom_texture.c
>> +++ b/src/mesa/state_tracker/st_atom_texture.c
>> @@ -148,9 +148,7 @@ compute_texture_format_swizzle(GLenum baseFormat, GLenum depthMode,
>>        else
>>           return SWIZZLE_XYZW;
>>     case GL_STENCIL_INDEX:
>> -      return SWIZZLE_XYZW;
>>     case GL_DEPTH_STENCIL:
>> -      /* fall-through */
>>     case GL_DEPTH_COMPONENT:
>>        /* Now examine the depth mode */
>>        switch (depthMode) {
>>
>
> A while ago I noticed and asked about the interaction with gallium
> formats. The problem is that for gallium this would be more like a
> "green" swizzle, since according to current format definitions stencil
> is always the second channel, i.e PIPE_FORMAT_S8_UINT has a channel
> swizzle of _x__, PIPE_FORMAT_X24S8_UINT _y__ and so on. This is a

Hrmph... do these swizzles get applied anywhere, or just "in the
spec"? FWIW nouveau just returns stencil-in-all-channels for
stencil-only formats. I guess util/formats.csv has it as you
described, but I'm not sure that gets applied anywhere.

> d3d10-ism really, but because it is legal in gallium to sample formats
> which have both depth and stencil the channel swizzle cannot be
> described consistently (this could be fixed by requiring depth-only or
> stencil-only formats for sampler views).
> Albeit for border color, we still need the "red" component (d310, of
> course, doesn't have any problem there, since border color is impossible
> with int/uint formats).
> But this change is ok by me, it doesn't really make things worse...

It didn't at all fix the dEQP tests I was hoping it would fix, but it
seems like the right thing. I think there's a lot of confusion around
what goes in what channel for depth/stencil. If all drivers can agree
on something consistent, we can implement that here too.

  -ilia