nir_build_frag_coord generates the correct sysval loads based on NIR
options. nir_load_frag_coord shouldn't be used directly because drivers
don't have to support it.
v2: RADV can't use it because nir->options isn't set, so use load_pixel_coord.
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41227>
The old calculation depended on the sample count, and gave subpar
results for 8x MSAA with standard sample locations. The new calculation
is based on the Intel pass, with some changing of the constants so that
the sample count is always proportional to alpha for 2xMSAA and 4xMSAA
and the addition of rotating the sample mask based on the pixel.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39335>
