chiang

Since	19.0

bsdf  chiang(vector nn, vector tanV, float R_v, float R_s, float TT_v, float TT_s, float TRT_v, float TRT_s, float shift, vector absorption_coeff, float ior, ...)

Creates a BSDF for computation of the physically based hair model described in paper “A Practical and Controllable Hair and Fur Model for Production Path Tracing” by Chiang et al.

Suitable only for curve geometry.

See writing a PBR shader for information on BSDFs.

nn

bumped/shading normal

tanV

tangent vector along V

R_v

Longitudinal roughness value “v” for lobe R (section 4.1 of the paper)

R_s

Azimuthal roughness value “s” for lobe R (section 4.1 of the paper)

TT_v

Longitudinal roughness value “v” for lobe TT (section 4.1 of the paper)

TT_s

Azimuthal roughness value “s” for lobe TT (section 4.1 of the paper)

TRT_v

Longitudinal roughness value “v” for lobe TRT (section 4.1 of the paper)

TRT_s

Azimuthal roughness value “s” for lobe TRT (section 4.1 of the paper)

shift

Represents the cuticle angle, which affects the position of the specular highlight. Input range of -1 to 1 is internally mapped to -90 to 90 (eg meaning 3-degrees would be 3/90 = 0.03333)

absorption_coeff

The absorption coefficient (section 4.2 of the paper)

ior

Index of refraction (eg 1.55)