better anisotropy (needed for trans-mapped hair)

[Alessandro Padovani]

tested with blender 2.81a, daz studio 4.12.0.86, plugin commit d4f2664

I did some tests on anisotropy and what I found is that iray is clockwise while cycles is counter-clockwise and they are shifted by 90 degrees. Also the iray anisotropy seems to affect the roughness as well so we have to compensate for cycles.

The resulting equations are below together with sample renders, first iray then cycles.

if iray anisotropy > 0
cycles anisotropy = iray anisotropy
cycles anisotropy rotation = 0.75 - iray anisotropy rotation
cycles roughness = iray roughness * (1 + iray anisotropy)

A correct conversion of anisotropy is important especially for trans-mapped hair. Below an example with the G2F toulouse hair, first iray then the old plugin conversion, then the new conversion using the equations above.

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[Thomas Larsson]

The equations have been implemented but not tested. For some reason the is no Glossy Anisotropy in Toulouse hair for G2F, but instead there is Anisotropy 2.

[Alessandro Padovani]

In my tests I focus on iray to cycles conversions, since I believe it makes little sense to try to convert the whole set of 3delight shaders. So I always convert the 3delight shaders to the iray uber shader inside daz studio before exporting. This also converts the 3delight anisotropy 2 to the iray anisotropy in the toulouse hair. Moreover when Jessub Kim will get #7 done, converting to the uber shader will be mandatory.

Commit f1e68fd seems to work fine, marking as resolved. Thank you Thomas for the fast fix as always.