This moves the pre-computation offline and store the pre-computed
table in the binary. The pre-computed tables are quite small and are
not a concern with respect to binary size increase.
This rewrites the precomputation to use manually fitted
approximations for both burley and random walk.
The approximations fix a discrepancy between cycles and EEVEE
SSS translucency look. The absolute maximum error is below 2%.
I believe better results could be achieved with automatic fitting
tools.
Note that Cycles Burley translucency profile has some issues as it
does not give a smooth profile. The profile is biased near the end
of the lower radii. For this reason, the fit was done on a white
diffuse with (1,1,1) radii which does not exhibit this artifact.
Note that while this adds the profile for random walk, it isn't
currently used because the profile type is not yet passed down
the deferred path.
The fitting data can be found attached to this PR.
Pull Request: https://projects.blender.org/blender/blender/pulls/112512
Clément Foucault
e2cef1c713