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.

2 files changed, 61 insertions, 1 deletions

diff --git a/intern/cycles/kernel/osl/osl_closures.cpp b/intern/cycles/kernel/osl/osl_closures.cpp
index 581b38e65c0..8c7ae30725c 100644
--- a/intern/cycles/kernel/osl/osl_closures.cpp
+++ b/intern/cycles/kernel/osl/osl_closures.cpp
@@ -4,7 +4,7 @@
  * Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
  * All Rights Reserved.
  *
- * Modifications Copyright 2011, Blender Foundation.
+ * Modifications Copyright 2011-2018, Blender Foundation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -59,6 +59,7 @@
 #include "kernel/closure/bsdf_ashikhmin_shirley.h"
 #include "kernel/closure/bsdf_toon.h"
 #include "kernel/closure/bsdf_hair.h"
+#include "kernel/closure/bsdf_hair_principled.h"
 #include "kernel/closure/bsdf_principled_diffuse.h"
 #include "kernel/closure/bsdf_principled_sheen.h"
 #include "kernel/closure/volume.h"
@@ -176,6 +177,61 @@ BSDF_CLOSURE_CLASS_BEGIN(PrincipledSheen, principled_sheen, PrincipledSheenBsdf,
 	CLOSURE_FLOAT3_PARAM(PrincipledSheenClosure, params.N),
 BSDF_CLOSURE_CLASS_END(PrincipledSheen, principled_sheen)
 
+/* PRINCIPLED HAIR BSDF */
+class PrincipledHairClosure : public CBSDFClosure {
+public:
+	PrincipledHairBSDF params;
+
+	PrincipledHairBSDF *alloc(ShaderData *sd, int path_flag, float3 weight)
+	{
+		PrincipledHairBSDF *bsdf = (PrincipledHairBSDF*)bsdf_alloc_osl(sd, sizeof(PrincipledHairBSDF), weight, &params);
+		if(!bsdf) {
+			return NULL;
+		}
+
+		PrincipledHairExtra *extra = (PrincipledHairExtra*)closure_alloc_extra(sd, sizeof(PrincipledHairExtra));
+		if(!extra) {
+			return NULL;
+		}
+
+		bsdf->extra = extra;
+		return bsdf;
+	}
+
+	void setup(ShaderData *sd, int path_flag, float3 weight)
+	{
+		if(!skip(sd, path_flag, LABEL_GLOSSY))
+		{
+			PrincipledHairBSDF *bsdf = (PrincipledHairBSDF*)alloc(sd, path_flag, weight);
+			if (!bsdf)
+			{
+				return;
+			}
+
+			sd->flag |= (bsdf) ? bsdf_principled_hair_setup(sd, bsdf) : 0;
+		}
+	}
+};
+
+static ClosureParam *closure_bsdf_principled_hair_params()
+{
+	static ClosureParam params[] = {
+		CLOSURE_FLOAT3_PARAM(PrincipledHairClosure, params.N),
+		CLOSURE_FLOAT3_PARAM(PrincipledHairClosure, params.sigma),
+		CLOSURE_FLOAT_PARAM(PrincipledHairClosure, params.v),
+		CLOSURE_FLOAT_PARAM(PrincipledHairClosure, params.s),
+		CLOSURE_FLOAT_PARAM(PrincipledHairClosure, params.m0_roughness),
+		CLOSURE_FLOAT_PARAM(PrincipledHairClosure, params.alpha),
+		CLOSURE_FLOAT_PARAM(PrincipledHairClosure, params.eta),
+		CLOSURE_STRING_KEYPARAM(PrincipledHairClosure, label, "label"),
+		CLOSURE_FINISH_PARAM(PrincipledHairClosure)
+	};
+
+	return params;
+}
+
+CCLOSURE_PREPARE(closure_bsdf_principled_hair_prepare, PrincipledHairClosure)
+
 /* DISNEY PRINCIPLED CLEARCOAT */
 class PrincipledClearcoatClosure : public CBSDFClosure {
 public:
@@ -322,6 +378,9 @@ void OSLShader::register_closures(OSLShadingSystem *ss_)
 	register_closure(ss, "hair_transmission", id++,
 		bsdf_hair_transmission_params(), bsdf_hair_transmission_prepare);
 
+	register_closure(ss, "principled_hair", id++,
+		closure_bsdf_principled_hair_params(), closure_bsdf_principled_hair_prepare);
+
 	register_closure(ss, "henyey_greenstein", id++,
 		closure_henyey_greenstein_params(), closure_henyey_greenstein_prepare);
 	register_closure(ss, "absorption", id++,
diff --git a/intern/cycles/kernel/osl/osl_closures.h b/intern/cycles/kernel/osl/osl_closures.h
index 857cc84afd2..d9aeb9ab9fb 100644
--- a/intern/cycles/kernel/osl/osl_closures.h
+++ b/intern/cycles/kernel/osl/osl_closures.h
@@ -79,6 +79,7 @@ void closure_bsdf_microfacet_multi_ggx_fresnel_prepare(OSL::RendererServices *,
 void closure_bsdf_microfacet_multi_ggx_glass_fresnel_prepare(OSL::RendererServices *, int id, void *data);
 void closure_bsdf_microfacet_multi_ggx_aniso_fresnel_prepare(OSL::RendererServices *, int id, void *data);
 void closure_bsdf_principled_clearcoat_prepare(OSL::RendererServices *, int id, void *data);
+void closure_bsdf_principled_hair_prepare(OSL::RendererServices *, int id, void *data);
 
 #define CCLOSURE_PREPARE(name, classname)          \
 void name(RendererServices *, int id, void *data) \