[Mesa-dev] Help! CopyImageSubData is defeating me

[Ilia Mirkin]

On Sun, Jun 25, 2017 at 5:39 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On June 25, 2017 2:31:56 PM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>
>> On Sun, Jun 25, 2017 at 5:25 PM, Jason Ekstrand <jason at jlekstrand.net>
>> wrote:
>>>
>>> On June 25, 2017 1:40:09 PM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>
>>>> On Sun, Jun 25, 2017 at 4:33 PM, Jason Ekstrand <jason at jlekstrand.net>
>>>> wrote:
>>>>>>
>>>>>>
>>>>>> Anyone have thoughts on this? Am I being foolish for trying to hold
>>>>>> onto GL_RGBA4 texturing? (Any decision here also affects st/nine.)
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Yes.  Chances are that you're also doing texture views wrong.  Are
>>>>> there
>>>>> any
>>>>> 4444 formats supported on nvidia hardware?
>>>>
>>>>
>>>>
>>>> Well, any permutation of a 4444 format is easily supportable for
>>>> texturing.
>>>>
>>>> What's wrong with the texture views? Should be fine... unless I'm
>>>> missing something. It's really just this issue with RB <-> Texture
>>>> copies where the RB's internal format is GL_RGBA4 while the *real*
>>>> internal format is RGBA8. Texture views between e.g. RGB565 and
>>>> RGBA4444 should work fine (and the fb will fail to validate as one
>>>> might expect if one were to attach a GL_RGBA4 texture view of a
>>>> GL_RGB565 texture).
>>>
>>>
>>>
>>> But what if you have a 4444 and you render to as 4444 and then try to
>>> texture from it as 565?
>>
>>
>> If you have a 4444 texture and attach it to a FB, then that FB will
>> not be complete. So you can't render to it in the first place.
>
>
> Ok, then I'm confused as to how you have a copy_image problem.  Is the issue
> just that gallium won't let you CopyImageSubData into a texture you can't
> render into?  Why not just treat it as R16 when using it as a copy_image
> destination?

No, the issue is copying between a GL_RGBA4 RB and GL_RGBA4 texture.
Behind the scenes, the GL_RGBA4 RB gets upgraded to a
8-bit-per-channel format, while the GL_RGBA4 texture has a
4-bit-per-channel format. Then when trying to copy-image between them,
you have two totally differently-formatted textures.

  -ilia