[Mesa-dev] [PATCH 2/2] mesa/st: add ARB_texture_view support

[Jose Fonseca]

On 20/08/14 17:33, Ilia Mirkin wrote:
> On Wed, Aug 20, 2014 at 12:22 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>> On 20/08/14 17:14, Roland Scheidegger wrote:
>>>
>>> Am 20.08.2014 17:55, schrieb Ilia Mirkin:
>>>>
>>>> On Wed, Aug 20, 2014 at 11:47 AM, Jose Fonseca <jfonseca at vmware.com>
>>>> wrote:
>>>>>
>>>>> On 20/08/14 16:31, Ilia Mirkin wrote:
>>>>>>
>>>>>>
>>>>>> Hm, it's not tested. And you're right, that would (most likely) mess
>>>>>> up, since it would only have the pipe_resource's target. Any
>>>>>> suggestions on how to fix it? Should the target be added to
>>>>>> pipe_sampler_view?
>>>>>>
>>>>>> On Wed, Aug 20, 2014 at 11:25 AM, Roland Scheidegger
>>>>>> <sroland at vmware.com>
>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Didn't look at it that closely, but I'm pretty surprised this really
>>>>>>> works. One things ARB_texture_view can do is cast cube maps (and cube
>>>>>>> map arrays) to 2d arrays and vice versa (also 1d/2d to the respective
>>>>>>> array type), and we cannot express that in sampler views (yet) (we
>>>>>>> can't
>>>>>>> express it in surfaces neither but there it should not matter). Which
>>>>>>> means the type used in the shader for sampling will not match the
>>>>>>> sampler view, which sounds quite broken to me.
>>>>>>>
>>>>>>> Roland
>>>>>>>
>>>>>
>>>>> Probably the only sane thing to do eliminate the disctinction between
>>>>> PIPE_TEXTURE_FOO and PIPE_TEXTURE_FOO_ARRAY like  in
>>>>>
>>>>> https://urldefense.proofpoint.com/v1/url?u=http://msdn.microsoft.com/en-us/library/windows/desktop/ff476202.aspx&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=F4msKE2WxRzA%2BwN%2B25muztFm5TSPwE8HKJfWfR2NgfY%3D%0A&m=x03OmuVWAQgfFbsFB2SLMLwSYavxkU8Zsypu9lEIkpg%3D%0A&s=4b0ca75d91e6d53d92658d9e334cf2a73a01efe5667464c969f5c085409052ff
>>>>> ,
>>>>> e.g.,:
>>>>>
>>>>> enum pipe_texture_target {
>>>>>      PIPE_BUFFER           = 0,
>>>>>      PIPE_TEXTURE_1D       = 1,
>>>>>      PIPE_TEXTURE_2D       = 2,
>>>>>      PIPE_TEXTURE_3D       = 3,
>>>>>      PIPE_TEXTURE_CUBE     = 4, // Must have same layout as
>>>>> PIPE_TEXTURE_2D
>>>>>      PIPE_TEXTURE_RECT     = 5,
>>>>>      PIPE_TEXTURE_1D_ARRAY = PIPE_TEXTURE_1D,
>>>>>      PIPE_TEXTURE_2D_ARRAY = PIPE_TEXTURE_2D,
>>>>>      PIPE_TEXTURE_CUBE_ARRAY = PIPE_TEXTURE_CUBE,
>>>>>      PIPE_MAX_TEXTURE_TYPES
>>>>> };
>>>>>
>>>>>
>>>>> We could also remove PIPE_TEXTURE_CUBE and have cube-maps be
>>>>> PIPE_TEXTURE_2D
>>>>> with a flag, but that's probably a lot of work. Instead, drivers that
>>>>> want
>>>>> to be able to support ARB_texture_view will need to ensure
>>>>> PIPE_TEXTURE_CUBE/PIPE_TEXTURE_2D layout match.
>>>>
>>>>
>>>> Another quick + cheap alternative (at least looking at nv50/nvc0 code)
>>>> would be to pass a separate target parameter to
>>>> ->create_sampler_view(). That would be enough for nouveau, but perhaps
>>>> not more generally? Take a look at nv50_tex.c:nv50_create_texture_view
>>>> -- it also needs to work out the depth of the texture (presumably to
>>>> deal with out-of-bounds accesses) and that is written to the texture
>>>> info structure.
>>>
>>> Well that should be enough, but I don't think it fits out design.
>>
>>
>>
>>> We've
>>>
>>> encapsulated other "override" information like the format in the view
>>> already, and I see no reason why the target "cast" should be treated any
>>> different.
>>
>>
>> In other words, you're arguing for:
>>
>> diff --git a/src/gallium/include/pipe/p_state.h
>> b/src/gallium/include/pipe/p_state.h
>> index a82686b..c87ac4e 100644
>> --- a/src/gallium/include/pipe/p_state.h
>> +++ b/src/gallium/include/pipe/p_state.h
>> @@ -333,6 +333,7 @@ struct pipe_surface
>
> On struct pipe_sampler_view, I thought... unless I'm misunderstanding.

Yep. My mistake.

> This was also my first thought about fixing this after Roland pointed
> out the issue.
>
>>      struct pipe_reference reference;
>>      struct pipe_resource *texture; /**< resource into which this is a view
>> */
>>      struct pipe_context *context; /**< context this surface belongs to */
>> +   enum pipe_texture target;
>>      enum pipe_format format;
>>
>>      /* XXX width/height should be removed */
>>
>>
>> It's a fair point.  And I don't object that solution.
>>
>> Of course, for this to work, drivers will need to treat the _ARRAY and non
>> _ARRAY targets the same when determining the texture layout for this to
>> work.
>>
>>
>> I just felt this would be a good oportunity to slim down pipe_texture_target
>> too.  I'm not sure the _ARRAY distinction still matters at this level, but I
>> suppose it doesn't hurt.
>
> Such a cleanup would probably have to be done by someone with a better
> understanding of gallium than me. OTOH if you guys feel like doing it
> the sampler_view way will accrue too much technical debt, that's fine
> too. Unless I hear otherwise, I'm going to try to do it the
> pipe_sampler_view way tonight.
>
>    -ilia
>