[Mesa-dev] [RFC] gallium: add interface for writable shader images

[Ilia Mirkin]

On Tue, Jul 7, 2015 at 4:35 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 07/07/15 21:28, Ilia Mirkin wrote:
>>
>> On Tue, Jul 7, 2015 at 4:24 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>>>
>>> I'm not experienced with the semantics around resources that can be
>>> read/written by shaders, so I can't really make educated comments.
>>>
>>> But overall this looks good to me FWIW.
>>>
>>> On 05/07/15 14:25, Marek Olšák wrote:
>>>>
>>>>
>>>> From: Marek Olšák <marek.olsak at amd.com>
>>>>
>>>> Other approaches are being considered:
>>>>
>>>> 1) Don't use resource wrappers (views) and pass all view parameters
>>>>      (format, layer range, level) to set_shader_images just like
>>>>      set_vertex_buffers, set_constant_buffer, or even glBindImageTexture
>>>> do.
>>>
>>>
>>>
>>> I don't know how much pipe drivers leverage this nowadays, but these
>>> structures are convenient placeholders for driver data, particular when
>>> they
>>> don't support something (e.g., a certain format, or need some swizzling),
>>> natively.
>>>
>>>>
>>>> 2) Use pipe_sampler_view instead of pipe_image_view,
>>>>      and maybe even use set_sampler_views instead of set_shader_images.
>>>>      set_sampler_views would have to use start_slot >= PIPE_MAX_SAMPLERS
>>>> for
>>>>      all writable images to allow for OpenGL textures in the lower
>>>> slots.
>>>
>>>
>>>
>>> If pipe_sampler_view  and pipe_image_view are the same, we could indeed
>>> use
>>> one structure for both.  While still keeping the separate
>>> create/bind/destroy functions.
>>
>>
>> The big difference is that a sampler view has a first/last layer and
>> first/last level, while image views are more like surfaces which just
>> have the one of each. But they also need a byte range for buffer
>> images.
>
>
> D3D11_TEX2D_ARRAY_UAV allows to specify first/last layer
> https://msdn.microsoft.com/en-us/library/windows/desktop/ff476242.aspx , so
> it sounds that once pipe_image_view is updated to handle D3D11, the
> difference would reduce to the absence of last_level

Erm. Duh. OpenGL needs first/last layer too. And pipe_surface has it
too, so it all works out well :)

>
>> Of course we could just ignore that and guarantee that first==last for
>> images.
>
>
> Yes, it might not be a bad idea.
>
> Jose