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

[Roland Scheidegger]

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
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...

Roland