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This will change the size of the lobe across the hair fiber. It behaves just like roughness for other BSDFs. This will change the size of the lobe along the length of the hair. This means changing these weights can change the look of the hair but will generally not make it brighter overall. Note that with values greater than 1, internal normalization might be done in order to avoid energy amplification by the BSDF. This scales the contribution of each lobe. Here is a description of each parameter of the hair_component closure: Weight * hair_component( lobe, longitudinal_roughness, azimuthal_roughness, hair_scales_tilt ) The general form of the hair closure looks like this: We choose to break down the model into sub-components with each component being one lobe of the BRDF and is specified by a closure. It supports a variable number of major lobes, usually named R, TT, TRT, etc which specify different paths that a light ray can take inside a hair fiber. The hair BSDF is a fairly complex function which simulates several effects observed on real hair fibers.
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Models a diffuse reflector based on the Oren-Nayar model. Models an anisotropic Cook-Torrance BRDF. A "gamma" parameter can be supplied to control the "tail" of the highlight to model highly realistic materials. This model can handle reflection, refraction or both at the same time. Models isotropic or anisotropic GGX BRDF.