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

[Ilia Mirkin]

That's actually stronger than saying that you'll leave them alone...
and probably better. Undefined sounds great to me!

On Mon, Jun 12, 2017 at 3:13 PM, Brian Paul <brianp at vmware.com> wrote:
> 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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>>>
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