wireblinn VEX function
Context: surface
See also: wirediffuse, Writing a PBR shader

bsdf wireblinn(vector tangent, float exponent)
Blinn function defined around a tangent vector. You can use this to produce the average specular illumination for thin wirelike primitives such as hair.

tangent
– tangent vector along the hair. 
exponent
– blinn exponent.