[Mesa-dev] Required-for-rendering internal formats

[Ilia Mirkin]

Anyone else have opinions on this? Should st/mesa be adding
PIPE_BIND_RENDER_TARGET for all textures of the internal formats
listed in table 8.12? (Which would, in this case, force RGBA8 to be
used since RGBA4 is non-renderable.) Or is it perfectly legal for a
format to be not renderable when used as a texture vs renderbuffer?

On Wed, Sep 7, 2016 at 1:19 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> Right, but it'd break st/nine which doesn't (didn't?) support
> fallbacks like st/mesa does.
>
> I'm trying to better understand what the required logic is based on
> the spec, not how to fix this particular application's rendering with
> nouveau (which I'm much less concerned about, tbh).
>
>   -ilia
>
> On Wed, Sep 7, 2016 at 1:16 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> Dropping texturing support for RGBA4 would resolve that issue.
>>
>> Marek
>>
>> On Wed, Sep 7, 2016 at 5:43 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>> Hello,
>>>
>>> Is there a concept in OpenGL that certain internal formats *must* be
>>> supported for rendering? An issue we're running into is that NVIDIA
>>> hardware supports sampling from RGBA4 textures, but does not support
>>> that as a render format. So if you create a tex image with GL_RGBA4,
>>> we use that as the TexFormat, since we can sample from it. However
>>> then attaching the image to a fbo makes that fbo incomplete.
>>>
>>> At least one application isn't ready to handle that situation. Is the
>>> application wrong, or must we support GL_RGBA4 as a renderable texture
>>> attachment format, thus meaning that we should never actually make use
>>> of the hw's RGBA4 sampling capabilities (since we never know if a
>>> texture will later be used for rendering)?
>>>
>>> The spec is a bit unclear about this. Table 8.12 of the GL 4.5 core
>>> spec marks GL_RGBA4 as "required renderable", but I think that only
>>> affects renderbuffers (which st/mesa handles properly by falling back
>>> to RGBA8 when the requested format is not renderable).
>>>
>>> Any advice welcome.
>>>
>>> Cheers,
>>>
>>>   -ilia
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