[Mesa-dev] [PATCH] gallivm: add a horrible hack for stencil texturing with border

[Marek Olšák]

On Wed, Dec 16, 2015 at 5:18 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 16.12.2015 um 12:52 schrieb Marek Olšák:
>> This is not well defined in gallium, but r600g and radeonsi use these
>> default swizzles for depth and stencil surfaces and it's probably the
>> only reasonable thing to do:
>>
>> Format = Default swizzle
>> Z24X8 = XXXX (Z)
>> Z24S8 = XXXX (Z)
>> X24S8 = YYYY (S)
>> X8Z24 = YYYY (Z)
>> S8Z24 = YYYY (Z)
>> S8X24 = XXXX (S)
>> Z32_S8X24 = XXXX (Z)
>> X32_S8X24 = YYYY (S)
>
> I suppose you also get the right border color without any hacks?

Border colors are somewhat broken on radeon due to hw design reasons,
so usually no and I can't do anything about it.

> I guess in theory these formats could use replicated swizzles in the
> u_format description, instead of only the one-channel ones. That would
> give the right result without doing anything special in drivers
> following those bits. However, it can't be done consistently, since it
> obviously won't work for depthstencil formats (which are still valid in
> gallium for texturing, albeit it would be possible to change that and
> enforce D24X8 views to be used instead).

Yeah that would work too.

> And this wouldn't do anything for the fact you can't get the right bits
> for stencil border color automatically that way (which is more
> problematic since no matter the format swizzling or sampler state
> swizzling it will always be wrong). (FWIW d3d10 decidedly uses the "G"
> channel for stencil, and you'd supposedly get R = B = 0, G = S, A = 1 -
> albeit there's no stencil-only S8 format, and since it's not possible to
> use integer textures with ordinary sampling just ld, there's no sampler,
> no border, no problem there...)

Well, st/mesa could set the border color to (d,d,d,d) for depth and
(s,s,s,s) for stencil, so that it works with any hardware behavior we
may get.

Marek