MaterialX Standard Surface shader has Subsurface Anisotropy parameter (
subsurface_anisotropy). The tooltip of this parameter, as well as its docs entry, state the following:The direction of subsurface scattering. 0 scatters light evenly, positive values scatter forward and negative values scatter backward.
In Houdini 19.5.640 it's not possible to set this parameter to negative values (and I recall that it was possible in older versions). For some reason, this parameter's lowest end of the range that it accepts is hardlocked to 0.
