chiang_fur

Since	20.0

bsdf  chiang_fur(vector nn, vector tanV, float mask, float cuticle, 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, float R2_v, float R2_s, vector R2_color, ...)

Creates a BSDF for computation of the physically based fur and hair model described in papers “A Practical and Controllable Hair and Fur Model for Production Path Tracing” by Chiang, “Physically-AccurAate Fur Reflectance: Modeling, Measurement and Rendering” by Ling-Qi Yan et al. Chiang Fur is an extension of the Chiang model - shader. This model considers a structural feature of fur and thick hair: the so-called medulla. Hair and fur have three main components:

Suitable only for curve geometry.

See writing a PBR shader for information on BSDFs.

nn

bumped/shading normal

tanV

tangent vector along V

mask

Masking main lobes in favour of medulla

cuticle

Modulates fresnel factor of the hair’s outermost layer

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)

R2_v

Longitudinal roughness value “v” of extra lobe R2

R2_s

Azimuthal roughness value “s” of extra lobe R2

R2_color

Extra R2 lobes has a color input to colorize the reflection. This could be used to promote iridescence colors for example.