[Mesa-dev] [RFC PATCH] gallium/nir: Add shader-based blending helpers

[Alyssa Rosenzweig]

> I would love to see this up in src/compiler/nir.

Is there a compelling reason to have it in NIR rather in Gallium, adding
an extra layer of translation overhead / indirection when coming from
Gallium blend state? (Mythical future Vulkan support, I guess?)

> Also, we should probably convert vc4 over in the process, so it's not
> just new unused code.

Probably. This version of the patch is pretty close to the _f blend
functions in vc4, so it should be at least partially drop-in. I'd love
to get the corresponding Panfrost code upstreamed as well, but for
$REASONS that probably can't happen yet.

> I'm also hoping that at some point I can figure out how to represent
> the TLB loads properly in NIR (with respect to multisampling, in
> particular) so that we can move the whole blend pipeline up.

It's worth noting that for us, because we're in the wacky dedicated
shader stage, it's unclear whether that would actually help. I'll need
to poke harder, I guess ;)

I haven't considered how MSAA interacts with this, ick...