[Mesa-dev] [PATCH] mesa/st: In the precense of integer buffers enable per buffer blending

Kenneth Graunke kenneth at whitecape.org
Tue Sep 25 22:48:13 UTC 2018

On Tuesday, September 25, 2018 4:20:04 PM CEST Ilia Mirkin wrote:
> I haven't double-checked yet, but doesn't this result in a reduction
> of functionality for pre-independent-blend GPUs (like the early NVIDIA
> Tesla series)? Configuring blending for an integer RT does nothing on
> NVIDIA hardware, so it all works out there just fine...
> Perhaps both patches should just be reverted and keep things as they
> were, and let drivers worry about this?

I mean, maybe, but seeing as blending is non-sensical for integer RTs,
and all of the settings are meaningless...it's really nice to have the
state tracker just clean this up.  As I said in my patches, it also
should improve CSO cache hits by making more state combinations become
identical...which might also be nice.

Fundamentally, you /are/ doing different blending settings per render
target in the presence of integer buffers.  I figured this couldn't
possibly have worked in that case.  But, as you said, it does.

I don't know.  Seems like modern HW really wants things to work
differently than old HW.  Maybe old HW drivers can be the ones to
carry the burden since there are fewer of them.  They could look
for any blend state that isn't all 0's.  Or, we could make st skip
this for drivers without per-RT blending caps.  Or, just ensure that
set_blend_state's blend[0] is a non-integer setting for those drivers,

This is my first time contributing to Gallium and I'd really like the
answer to every patch I send to not be "we can't make the common
framework do that, please foist the problem back onto your driver". :(
At the same time, I know we can't break them...sorry about not thinking
about it...
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