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

[Ilia Mirkin]

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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