[Mesa-dev] [PATCH] i965/fs: Don't use the pixel interpolater for centroid interpolation

Neil Roberts neil at linux.intel.com
Wed Jul 1 06:30:57 PDT 2015

Ben Widawsky <ben at bwidawsk.net> writes:

> I am not the right person to judge the complexity tradeoff, but it
> seems like a worthwhile patch to me. I spent a few minutes thinking
> about how it could hurt performance and was unable to come up with
> anything.

Thanks. I was thinking more that the complexity means more code to
maintain rather than that it would be a performance hit. If we have this
patch and another patch to make it not fall back to SIMD8 then using
interpolateAtCentroid ends up being exactly the same as using the
centroid interpolation qualifier on the varying except that it is more
convenient because you don't need to put it in the vertex shader as
well. However I think centroid interpolation is a pretty obscure feature
that is only useful if you're doing multisampling with an algorithm that
breaks if it is used for samples that lie outside of the polygon, so
maybe it's not really worth worrying about.

- Neil

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