[Mesa-dev] Help! CopyImageSubData is defeating me

[Ilia Mirkin]

On Sun, Jun 25, 2017 at 6:24 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> On 25.06.2017 23:42, Ilia Mirkin wrote:
>>
>> 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.
>
>
> Bind the GL_RGBA4 destination texture as a GL_RG8UI or GL_R16UI surface and
> render to it using a shader that does the conversion manually?

Right, so there are 2 directions here... RGBA4 -> RGBA8 I can do with
a plain blit. RGBA8 -> RGBA4 I need to do something custom, like you
said.

Do I also need to worry about component ordering? The RGBA8 thing is
guaranteed to be the renderbuffer side, which I think has a lot less
opportunity for weirdness -- most of the texture weirdness comes from
glTexImage format/type options.

  -ilia