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

[Ilia Mirkin]

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.
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