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

[Marek Olšák]

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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