[Mesa-dev] [PATCH 1/2] gallium/docs: improve docs for SAMPLE_POS, SAMPLE_INFO, TXQS, MSAA semantics

[Brian Paul]

Or say they're undefined: sample pos = (x, y, undef, undef), for example.

I'd be OK with that.  You?

-Brian

On 06/12/2017 11:47 AM, Ilia Mirkin wrote:
> Perhaps this is wrong in the grand scheme of things, but at least
> nouveau will *only* set the defined components of dst, not the
> undefined ones. Perhaps we should zero those out?
>
> On Mon, Jun 12, 2017 at 1:37 PM, Brian Paul <brianp at vmware.com> wrote:
>> For the SAMPLE_POS and SAMPLE_INFO opcodes, clarify resource vs. render
>> target queries, range of postion values, swizzling, etc.  We basically
>> follow the DX10.1 conventions.
>>
>> For the TXQS opcode and TGSI_SEMANTIC_SAMPLEID, clarify return value
>> and type.
>>
>> For the TGSI_SEMANTIC_SAMPLEPOS system value, clarify the range of
>> positions returned.
>> ---
>>   src/gallium/docs/source/tgsi.rst | 53 +++++++++++++++++++++++++++++++---------
>>   1 file changed, 42 insertions(+), 11 deletions(-)
>>
>> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
>> index 7fb963f..310b49d 100644
>> --- a/src/gallium/docs/source/tgsi.rst
>> +++ b/src/gallium/docs/source/tgsi.rst
>> @@ -982,7 +982,9 @@ XXX doesn't look like most of the opcodes really belong here.
>>   .. opcode:: TXQS - Texture Samples Query
>>
>>     This retrieves the number of samples in the texture, and stores it
>> -  into the x component. The other components are undefined.
>> +  into the x component as an unsigned integer. The other components are
>> +  undefined.  If the texture is not multisampled, this function returns
>> +  (1, 0, 0, 0).
>>
>>   .. math::
>>
>> @@ -2538,14 +2540,40 @@ after lookup.
>>
>>   .. opcode:: SAMPLE_POS
>>
>> -  Query the position of a given sample.  dst receives float4 (x, y, 0, 0)
>> -  indicated where the sample is located. If the resource is not a multi-sample
>> -  resource and not a render target, the result is 0.
>> +  Query the position of a sample in the given resource or render target
>> +  when per-sample fragment shading is in effect.
>> +
>> +  Syntax: ``SAMPLE_POS dst, source, sample_index``
>> +
>> +  dst receives float4 (x, y, 0, 0) indicated where the sample is located.
>> +  Sample locations are in the range [0, 1] where 0.5 is the center of the
>> +  fragment.
>> +
>> +  source is either a sampler view (to indicate a shader resource) or temp
>> +  register (to indicate the render target).  The source register may have
>> +  an optional swizzle to apply to the returned result
>> +
>> +  sample_index is an integer scalar indicating which sample position is to
>> +  be queried.
>> +
>> +  If per-sample shading is not in effect or the source resource or render
>> +  target is not multisampled, the result is (0, 0, 0, 0).
>>
>>   .. opcode:: SAMPLE_INFO
>>
>> -  dst receives number of samples in x.  If the resource is not a multi-sample
>> -  resource and not a render target, the result is 0.
>> +  Query the number of samples in a multisampled resource or render target.
>> +
>> +  Syntax: ``SAMPLE_INFO dst, source``
>> +
>> +  dst receives int4 (n, 0, 0, 0) where n is the number of samples in a
>> +  resource or the render target.
>> +
>> +  source is either a sampler view (to indicate a shader resource) or temp
>> +  register (to indicate the render target).  The source register may have
>> +  an optional swizzle to apply to the returned result
>> +
>> +  If per-sample shading is not in effect or the source resource or render
>> +  target is not multisampled, the result is (1, 0, 0, 0).
>>
>>
>>   .. _resourceopcodes:
>> @@ -3284,15 +3312,18 @@ TGSI_SEMANTIC_SAMPLEID
>>   """"""""""""""""""""""
>>
>>   For fragment shaders, this semantic label indicates that a system value
>> -contains the current sample id (i.e. gl_SampleID).
>> -This is an integer value, and only the X component is used.
>> +contains the current sample id (i.e. gl_SampleID) as an unsigned int.
>> +Only the X component is used.  If per-sample shading is not enabled,
>> +the result is (0, 0, 0, 0).
>>
>>   TGSI_SEMANTIC_SAMPLEPOS
>>   """""""""""""""""""""""
>>
>> -For fragment shaders, this semantic label indicates that a system value
>> -contains the current sample's position (i.e. gl_SamplePosition). Only the X
>> -and Y values are used.
>> +For fragment shaders, this semantic label indicates that a system
>> +value contains the current sample's position as float4(x, y, 0, 0) in
>> +the render target (i.e.  gl_SamplePosition) when per-fragment shading
>> +is in effect.  Position values are in the range [0, 1] where 0.5 is
>> +the center of the fragment.
>>
>>   TGSI_SEMANTIC_SAMPLEMASK
>>   """"""""""""""""""""""""
>> --
>> 1.9.1
>>
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