[Mesa-dev] [PATCH 2/4] gallium: add new properties for clip and cull distance usage

[Ilia Mirkin]

AMD/NVIDIA hardware has a limit on how many cull/clip distances can be
used at a time. On NVIDIA hw, there's a bitmask which you flip to
determine if a distance is meant to clip or cull. It's nice not to
have to analyze the output writes of a shader to tell how many clip
distances are used.

On Mon, Oct 19, 2015 at 5:02 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> I don't have anything against new properties but why exactly is it
> needed? As far as I can tell, clip/cull distances aren't declared as
> arrays but just (up to two each) ordinary outputs, thus using the usage
> masks should work just fine. Or is this handled differently by some
> shader stages?
>
> Roland
>
> Am 18.10.2015 um 19:14 schrieb Marek Olšák:
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> The TGSI usage mask can't be used, because these are declared as an output
>> array of 2 elements.
>> ---
>>  src/gallium/auxiliary/tgsi/tgsi_strings.c  |  2 ++
>>  src/gallium/docs/source/tgsi.rst           | 10 ++++++++++
>>  src/gallium/include/pipe/p_shader_tokens.h |  4 +++-
>>  3 files changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_strings.c b/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> index 8271ea0..89369d6 100644
>> --- a/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> +++ b/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> @@ -137,6 +137,8 @@ const char *tgsi_property_names[TGSI_PROPERTY_COUNT] =
>>     "TES_SPACING",
>>     "TES_VERTEX_ORDER_CW",
>>     "TES_POINT_MODE",
>> +   "NUM_CLIPDIST_ENABLED",
>> +   "NUM_CULLDIST_ENABLED",
>>  };
>>
>>  const char *tgsi_return_type_names[TGSI_RETURN_TYPE_COUNT] =
>> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
>> index 314fe1b..01e18f3 100644
>> --- a/src/gallium/docs/source/tgsi.rst
>> +++ b/src/gallium/docs/source/tgsi.rst
>> @@ -3126,6 +3126,16 @@ TES_POINT_MODE
>>  If set to a non-zero value, this turns on point mode for the tessellator,
>>  which means that points will be generated instead of primitives.
>>
>> +NUM_CLIPDIST_ENABLED
>> +""""""""""""""""
>> +
>> +How many clip distance scalar outputs are enabled.
>> +
>> +NUM_CULLDIST_ENABLED
>> +""""""""""""""""
>> +
>> +How many cull distance scalar outputs are enabled.
>> +
>>
>>  Texture Sampling and Texture Formats
>>  ------------------------------------
>> diff --git a/src/gallium/include/pipe/p_shader_tokens.h b/src/gallium/include/pipe/p_shader_tokens.h
>> index b36e0a3..e0ab901 100644
>> --- a/src/gallium/include/pipe/p_shader_tokens.h
>> +++ b/src/gallium/include/pipe/p_shader_tokens.h
>> @@ -267,7 +267,9 @@ union tgsi_immediate_data
>>  #define TGSI_PROPERTY_TES_SPACING            12
>>  #define TGSI_PROPERTY_TES_VERTEX_ORDER_CW    13
>>  #define TGSI_PROPERTY_TES_POINT_MODE         14
>> -#define TGSI_PROPERTY_COUNT                  15
>> +#define TGSI_PROPERTY_NUM_CLIPDIST_ENABLED   15
>> +#define TGSI_PROPERTY_NUM_CULLDIST_ENABLED   16
>> +#define TGSI_PROPERTY_COUNT                  17
>>
>>  struct tgsi_property {
>>     unsigned Type         : 4;  /**< TGSI_TOKEN_TYPE_PROPERTY */
>>
>
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