Cycles: add Principled Hair BSDF.

This is a physically-based, easy-to-use shader for rendering hair and fur,
with controls for melanin, roughness and randomization.

Based on the paper "A Practical and Controllable Hair and Fur Model for
Production Path Tracing".

Implemented by Leonardo E. Segovia and Lukas Stockner, part of Google
Summer of Code 2018.

1 files changed, 39 insertions, 0 deletions

diff --git a/intern/cycles/render/nodes.h b/intern/cycles/render/nodes.h
index ebe6db6e362..28bbe2de05a 100644
--- a/intern/cycles/render/nodes.h
+++ b/intern/cycles/render/nodes.h
@@ -608,6 +608,45 @@ public:
 	float temperature;
 };
 
+/* Interface between the I/O sockets and the SVM/OSL backend. */
+class PrincipledHairBsdfNode : public BsdfBaseNode {
+public:
+	SHADER_NODE_CLASS(PrincipledHairBsdfNode)
+	void attributes(Shader *shader, AttributeRequestSet *attributes);
+
+	/* Longitudinal roughness. */
+	float roughness;
+	/* Azimuthal roughness. */
+	float radial_roughness;
+	/* Randomization factor for roughnesses. */
+	float random_roughness;
+	/* Longitudinal roughness factor for only the diffuse bounce (shiny undercoat). */
+	float coat;
+	/* Index of reflection. */
+	float ior;
+	/* Cuticle tilt angle. */
+	float offset;
+	/* Direct coloring's color. */
+	float3 color;
+	/* Melanin concentration. */
+	float melanin;
+	/* Melanin redness ratio. */
+	float melanin_redness;
+	/* Dye color. */
+	float3 tint;
+	/* Randomization factor for melanin quantities. */
+	float random_color;
+	/* Absorption coefficient (unfiltered). */
+	float3 absorption_coefficient;
+
+	float3 normal;
+	float surface_mix_weight;
+	/* If linked, here will be the given random number. */
+	float random;
+	/* Selected coloring parametrization. */
+	NodePrincipledHairParametrization parametrization;
+};
+
 class HairBsdfNode : public BsdfNode {
 public:
 	SHADER_NODE_CLASS(HairBsdfNode)