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.

9 files changed, 174 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index 8e54c6a87c4..23ef45416f7 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -794,6 +794,8 @@ struct ShadeResult;
 #define SH_NODE_DISPLACEMENT            198
 #define SH_NODE_VECTOR_DISPLACEMENT     199
 #define SH_NODE_VOLUME_PRINCIPLED       200
+/* 201..700 occupied by other node types, continue from 701 */
+#define SH_NODE_BSDF_HAIR_PRINCIPLED    701
 
 /* custom defines options for Material node */
 #define SH_NODE_MAT_DIFF   1
diff --git a/source/blender/blenkernel/intern/node.c b/source/blender/blenkernel/intern/node.c
index f15d90100d2..c830917a547 100644
--- a/source/blender/blenkernel/intern/node.c
+++ b/source/blender/blenkernel/intern/node.c
@@ -3622,6 +3622,7 @@ static void registerShaderNodes(void)
 	register_node_type_sh_bsdf_velvet();
 	register_node_type_sh_bsdf_toon();
 	register_node_type_sh_bsdf_hair();
+	register_node_type_sh_bsdf_hair_principled();
 	register_node_type_sh_emission();
 	register_node_type_sh_holdout();
 	register_node_type_sh_volume_absorption();
diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index 23df1b72c37..6e52af2898e 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -1111,6 +1111,11 @@ static void node_shader_buts_hair(uiLayout *layout, bContext *UNUSED(C), Pointer
 	uiItemR(layout, ptr, "component", 0, "", ICON_NONE);
 }
 
+static void node_shader_buts_principled_hair(uiLayout *layout, bContext *UNUSED(C), PointerRNA *ptr)
+{
+	uiItemR(layout, ptr, "parametrization", 0, "", ICON_NONE);
+}
+
 static void node_shader_buts_ies(uiLayout *layout, bContext *UNUSED(C), PointerRNA *ptr)
 {
 	uiLayout *row;
@@ -1301,6 +1306,9 @@ static void node_shader_set_butfunc(bNodeType *ntype)
 		case SH_NODE_BSDF_HAIR:
 			ntype->draw_buttons = node_shader_buts_hair;
 			break;
+		case SH_NODE_BSDF_HAIR_PRINCIPLED:
+			ntype->draw_buttons = 	node_shader_buts_principled_hair;
+			break;
 		case SH_NODE_SCRIPT:
 			ntype->draw_buttons = node_shader_buts_script;
 			ntype->draw_buttons_ex = node_shader_buts_script_ex;
diff --git a/source/blender/makesdna/DNA_node_types.h b/source/blender/makesdna/DNA_node_types.h
index 00758bd1379..5c692cf85da 100644
--- a/source/blender/makesdna/DNA_node_types.h
+++ b/source/blender/makesdna/DNA_node_types.h
@@ -963,6 +963,11 @@ typedef struct NodeCryptomatte {
 #define SHD_HAIR_REFLECTION		0
 #define SHD_HAIR_TRANSMISSION		1
 
+/* principled hair parametrization */
+#define SHD_PRINCIPLED_HAIR_REFLECTANCE				0
+#define SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION	1
+#define SHD_PRINCIPLED_HAIR_DIRECT_ABSORPTION		2
+
 /* blend texture */
 #define SHD_BLEND_LINEAR			0
 #define SHD_BLEND_QUADRATIC			1
diff --git a/source/blender/makesrna/intern/rna_nodetree.c b/source/blender/makesrna/intern/rna_nodetree.c
index 52fbadd0f54..b41e9b1c4e5 100644
--- a/source/blender/makesrna/intern/rna_nodetree.c
+++ b/source/blender/makesrna/intern/rna_nodetree.c
@@ -3350,6 +3350,13 @@ static const EnumPropertyItem node_hair_items[] = {
 	{0, NULL, 0, NULL, NULL}
 };
 
+static const EnumPropertyItem node_principled_hair_items[] = {
+	{SHD_PRINCIPLED_HAIR_DIRECT_ABSORPTION,     "ABSORPTION", 0, "Absorption coefficient",   "Directly set the absorption coefficient sigma_a. This is not the most intuitive way to color hair."},
+	{SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION, "MELANIN",    0, "Melanin concentration",    "Define the melanin concentrations below to get the most realistic-looking hair. You can get the concentrations for different types of hair online."},
+	{SHD_PRINCIPLED_HAIR_REFLECTANCE,           "COLOR",      0, "Direct coloring",          "Choose the color of your preference, and the shader will approximate the absorption coefficient to render lookalike hair."},
+	{0, NULL, 0, NULL, NULL}
+};
+
 static const EnumPropertyItem node_script_mode_items[] = {
 	{NODE_SCRIPT_INTERNAL, "INTERNAL", 0, "Internal", "Use internal text data-block"},
 	{NODE_SCRIPT_EXTERNAL, "EXTERNAL", 0, "External", "Use external .osl or .oso file"},
@@ -4409,6 +4416,21 @@ static void def_hair(StructRNA *srna)
 	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_Node_update");
 }
 
+/* RNA initialization for the custom property. */
+static void def_hair_principled(StructRNA *srna)
+{
+	PropertyRNA *prop;
+
+	prop = RNA_def_property(srna, "parametrization", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "custom1");
+	RNA_def_property_ui_text(prop, "Color parametrization", "Select the shader's color parametrization");
+	RNA_def_property_enum_items(prop, node_principled_hair_items);
+	RNA_def_property_enum_default(prop, SHD_PRINCIPLED_HAIR_REFLECTANCE);
+	/* Upon editing, update both the node data AND the UI representation */
+	/* (This effectively shows/hides the relevant sockets) */
+	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_ShaderNode_socket_update");
+}
+
 static void def_sh_uvmap(StructRNA *srna)
 {
 	PropertyRNA *prop;
diff --git a/source/blender/nodes/CMakeLists.txt b/source/blender/nodes/CMakeLists.txt
index 5a5d5997878..7ef41b25de8 100644
--- a/source/blender/nodes/CMakeLists.txt
+++ b/source/blender/nodes/CMakeLists.txt
@@ -173,6 +173,7 @@ set(SRC
 	shader/nodes/node_shader_bsdf_transparent.c
 	shader/nodes/node_shader_bsdf_velvet.c
 	shader/nodes/node_shader_bsdf_hair.c
+	shader/nodes/node_shader_bsdf_hair_principled.c
 	shader/nodes/node_shader_bump.c
 	shader/nodes/node_shader_emission.c
 	shader/nodes/node_shader_fresnel.c
diff --git a/source/blender/nodes/NOD_shader.h b/source/blender/nodes/NOD_shader.h
index ca604363e35..d4134f09597 100644
--- a/source/blender/nodes/NOD_shader.h
+++ b/source/blender/nodes/NOD_shader.h
@@ -116,6 +116,7 @@ void register_node_type_sh_volume_absorption(void);
 void register_node_type_sh_volume_scatter(void);
 void register_node_type_sh_volume_principled(void);
 void register_node_type_sh_bsdf_hair(void);
+void register_node_type_sh_bsdf_hair_principled(void);
 void register_node_type_sh_subsurface_scattering(void);
 void register_node_type_sh_mix_shader(void);
 void register_node_type_sh_add_shader(void);
diff --git a/source/blender/nodes/NOD_static_types.h b/source/blender/nodes/NOD_static_types.h
index a4f8a798576..2fa8cda56a5 100644
--- a/source/blender/nodes/NOD_static_types.h
+++ b/source/blender/nodes/NOD_static_types.h
@@ -89,6 +89,7 @@ DefNode( ShaderNode,     SH_NODE_BSDF_TRANSPARENT,   0,                      "BS
 DefNode( ShaderNode,     SH_NODE_BSDF_VELVET,        0,                      "BSDF_VELVET",        BsdfVelvet,       "Velvet BSDF",       ""       )
 DefNode( ShaderNode,     SH_NODE_BSDF_TOON,          def_toon,               "BSDF_TOON",          BsdfToon,         "Toon BSDF",         ""       )
 DefNode( ShaderNode,     SH_NODE_BSDF_HAIR,          def_hair,               "BSDF_HAIR",          BsdfHair,         "Hair BSDF",         ""       )
+DefNode( ShaderNode,     SH_NODE_BSDF_HAIR_PRINCIPLED,  def_hair_principled, "BSDF_HAIR_PRINCIPLED", BsdfHairPrincipled,  "Principled Hair BSDF", "")
 DefNode( ShaderNode,     SH_NODE_SUBSURFACE_SCATTERING, def_sh_subsurface,   "SUBSURFACE_SCATTERING",SubsurfaceScattering,"Subsurface Scattering","")
 DefNode( ShaderNode,     SH_NODE_VOLUME_ABSORPTION,  0,                      "VOLUME_ABSORPTION",  VolumeAbsorption, "Volume Absorption", ""       )
 DefNode( ShaderNode,     SH_NODE_VOLUME_SCATTER,     0,                      "VOLUME_SCATTER",     VolumeScatter,    "Volume Scatter",    ""       )
diff --git a/source/blender/nodes/shader/nodes/node_shader_bsdf_hair_principled.c b/source/blender/nodes/shader/nodes/node_shader_bsdf_hair_principled.c
new file mode 100644
index 00000000000..c5029852033
--- /dev/null
+++ b/source/blender/nodes/shader/nodes/node_shader_bsdf_hair_principled.c
@@ -0,0 +1,133 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2018 Blender Foundation.
+ * All rights reserved.
+ *
+ * The Original Code is: all of this file.
+ *
+ * Contributor(s): Lukas Stockner, L. E. Segovia
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+#include "../node_shader_util.h"
+
+/* **************** OUTPUT ******************** */
+
+/* Color, melanin and absorption coefficient default to approximately same brownish hair. */
+static bNodeSocketTemplate sh_node_bsdf_hair_principled_in[] = {
+	{	SOCK_RGBA,		1, N_("Color"),						0.017513f, 0.005763f, 0.002059f, 1.0f, 0.0f, 1.0f},
+	{	SOCK_FLOAT,		1, N_("Melanin"),					0.8f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT,		1, N_("Melanin Redness"),			1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_RGBA,		1, N_("Tint"),						1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f},
+	{	SOCK_VECTOR,	1, N_("Absorption Coefficient"),	0.245531f, 0.52f, 1.365f, 0.0f, 0.0f, 1000.0f},
+	{	SOCK_FLOAT,		1, N_("Roughness"),					0.3f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT,		1, N_("Radial Roughness"),			0.3f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT,		1, N_("Coat"),						0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT,		1, N_("IOR"),						1.55f, 0.0f, 0.0f, 0.0f, 0.0f, 1000.0f},
+	{	SOCK_FLOAT,		1, N_("Offset"),					2.f*((float)M_PI)/180.f, 0.0f, 0.0f, 0.0f, -M_PI_2, M_PI_2, PROP_ANGLE},
+	{	SOCK_FLOAT, 	1, N_("Random Color"),				0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT, 	1, N_("Random Roughness"),			0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_FACTOR},
+	{	SOCK_FLOAT,		1, N_("Random"),					0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, PROP_NONE, SOCK_HIDE_VALUE},
+	{	-1, 0, ""	},
+};
+
+static bNodeSocketTemplate sh_node_bsdf_hair_principled_out[] = {
+	{	SOCK_SHADER, 0, N_("BSDF")},
+	{	-1, 0, ""	}
+};
+
+/* Initialize the custom Parametrization property to Color. */
+static void node_shader_init_hair_principled(bNodeTree *UNUSED(ntree), bNode *node)
+{
+	node->custom1 = SHD_PRINCIPLED_HAIR_REFLECTANCE;
+}
+
+/* Triggers (in)visibility of some sockets when changing Parametrization. */
+static void node_shader_update_hair_principled(bNodeTree *UNUSED(ntree), bNode *node)
+{
+	bNodeSocket *sock;
+	int parametrization = node->custom1;
+
+	for (sock = node->inputs.first; sock; sock = sock->next) {
+		if (STREQ(sock->name, "Color")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_REFLECTANCE) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+		else if (STREQ(sock->name, "Melanin")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+		else if (STREQ(sock->name, "Melanin Redness")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+		else if (STREQ(sock->name, "Tint")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+		else if (STREQ(sock->name, "Absorption Coefficient")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_DIRECT_ABSORPTION) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+		else if (STREQ(sock->name, "Random Color")) {
+			if (parametrization == SHD_PRINCIPLED_HAIR_PIGMENT_CONCENTRATION) {
+				sock->flag &= ~SOCK_UNAVAIL;
+			}
+			else {
+				sock->flag |= SOCK_UNAVAIL;
+			}
+		}
+	}
+}
+
+/* node type definition */
+void register_node_type_sh_bsdf_hair_principled(void)
+{
+	static bNodeType ntype;
+
+	sh_node_type_base(&ntype, SH_NODE_BSDF_HAIR_PRINCIPLED, "Principled Hair BSDF", NODE_CLASS_SHADER, 0);
+	node_type_compatibility(&ntype, NODE_NEW_SHADING);
+	node_type_socket_templates(&ntype, sh_node_bsdf_hair_principled_in, sh_node_bsdf_hair_principled_out);
+	node_type_size_preset(&ntype, NODE_SIZE_LARGE);
+	node_type_init(&ntype, node_shader_init_hair_principled);
+	node_type_storage(&ntype, "", NULL, NULL);
+	node_type_update(&ntype, node_shader_update_hair_principled, NULL);
+
+	nodeRegisterType(&ntype);
+}