[Mesa-dev] [PATCH 00/10] glsl: Implement varying packing.
aras at unity3d.com
Tue Dec 11 23:49:57 PST 2012
> For the initial implementation I've chosen a strategy that operates
> exclusively at the GLSL IR level, so that it doesn't require the
> cooperation of the driver back-ends.
Wouldn't this negatively affect performance of some GPUs?
Not sure if relevant for Mesa, but e.g. on PowerVR SGX it's really bad to
pack two vec2 texture coordinates into a single vec4. That's because var.xy
texture read can be "prefetched", whereas var.zw texture read is not
prefetched (essentially treated as a dependent texture read), and often
causes stalls in the shader execution.
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