[Mesa-dev] [PATCH 2/2] gallium/docs: clarify TGSI_SEMANTIC_SAMPLEMASK, again

[Nicolai Hähnle]

On 12.06.2017 19:37, Brian Paul wrote:
> I've since discovered the fragment shader sample mask input (which
> corresponds to gl_SampleMaskIn).
> ---
>   src/gallium/docs/source/tgsi.rst | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
> index 310b49d..7ca07dd 100644
> --- a/src/gallium/docs/source/tgsi.rst
> +++ b/src/gallium/docs/source/tgsi.rst
> @@ -3328,10 +3328,17 @@ the center of the fragment.
>   TGSI_SEMANTIC_SAMPLEMASK
>   """"""""""""""""""""""""
>   
> -For fragment shaders, this semantic label indicates that an output contains
> -the sample mask used to disable further sample processing.  The output's
> -type is uint[4] but only the X component is used (i.e. gl_SampleMask[0]).
> -Each bit corresponds to one sample position (up to 32x MSAA is supported).
> +For fragment shaders, this semantic label can be applied to either a
> +shader input or output.
> +
> +For an input, the sample mask indicates the set of samples covered by
> +the current primitive.  If MSAA is not enabled, the value is (~0, ~0, ~0, ~0).

This doesn't match radeonsi behavior. I think you may get (1, ?, ?, ?) 
without MSAA, although I've never tried, and if DX says you get ~0, then 
perhaps that's actually what our hardware does.

But what I'm certain about is that trying to use the yzw components will 
lead to a shader compiler assertion :-)

Cheers,
Nicolai


> +
> +For an output, the sample mask is used to disable further sample processing.
> +
> +For both inputs and outputs, the register type is uint[4] but only the X
> +component is used (i.e. gl_SampleMask[0]). Each bit corresponds to one
> +sample position (up to 32x MSAA is supported).
>   
>   TGSI_SEMANTIC_INVOCATIONID
>   """"""""""""""""""""""""""
> 


-- 
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Aber vergiss niemals, wie sie sein sollte.