Add Gooch Shading node to NPR library (#1674)

Initial implementation of a gooch_shade node to the NPR data library that represents Gooch Shading used for technical illustration.

libraries/nprlib/nprlib_defs.mtlx

@@ -39,4 +39,17 @@
     <output name="out" type="float" default="0.0" />
   </nodedef>
 
+  <!--
+    Node: <gooch_shade>
+    Compute Gooch Shading.
+  -->
+  <nodedef name="ND_gooch_shade" node="gooch_shade" nodegroup="npr" doc="Compute Gooch shading">
+    <input name="warm_color" type="color3" value="0.8, 0.8, 0.7" uiname="Warm Color" doc="Warm color" />
+    <input name="cool_color" type="color3" value="0.3, 0.3, 0.8" uiname="Cool Color" doc="Cool color" />
+    <input name="specular_intensity" type="float" value="1" uimin="0" uimax="1" uiname="Specular Intensity" doc="Specular Intensity" />
+    <input name="shininess" type="float" value="64" uimin="1" uisoftmax="256" uiname="Shininess" doc="Specular Power" />
+    <input name="light_direction" type="vector3" value="1, -0.5, -0.5" uiname="Light Direction" doc="Light vector in world space" />
+    <output name="out" type="color3"/>
+  </nodedef>
+
 </materialx>

libraries/nprlib/nprlib_ng.mtlx

@@ -44,4 +44,79 @@
     <output name="out" type="float" nodename="N_result" />
   </nodegraph>
 
+  <!--
+    Node: <gooch_shade>
+  -->
+  <nodegraph name="NG_gooch_shade" type="color3" nodedef="ND_gooch_shade">
+    <normal name="normal" type="vector3" />
+    <viewdirection name="viewdir" type="vector3" />
+    <normalize name="unit_normal" type="vector3">
+      <input name="in" type="vector3" nodename="normal" />
+    </normalize>
+    <normalize name="unit_viewdir" type="vector3">
+      <input name="in" type="vector3" nodename="viewdir" />
+    </normalize>
+    <normalize name="unit_lightdir" type="vector3">
+      <input name="in" type="vector3" interfacename="light_direction" />
+    </normalize>
+    <dotproduct name="NdotL" type="float">
+      <input name="in1" type="vector3" nodename="unit_normal" />
+      <input name="in2" type="vector3" nodename="unit_lightdir" />
+    </dotproduct>
+    <add name="one_plus_NdotL" type="float">
+      <input name="in2" type="float" nodename="NdotL" />
+      <input name="in1" type="float" value="1" />
+    </add>
+    <divide name="cool_intensity" type="float">
+      <input name="in1" type="float" nodename="one_plus_NdotL" />
+      <input name="in2" type="float" value="2" />
+    </divide>
+    <mix name="diffuse" type="color3">
+      <input name="bg" type="color3" interfacename="warm_color" />
+      <input name="fg" type="color3" interfacename="cool_color" />
+      <input name="mix" type="float" nodename="cool_intensity" />
+    </mix>
+    <dotproduct name="NdotV" type="float">
+      <input name="in1" type="vector3" nodename="unit_normal" />
+      <input name="in2" type="vector3" nodename="unit_viewdir" />
+    </dotproduct>
+    <multiply name="NdotV_2" type="float">
+      <input name="in1" type="float" nodename="NdotV" />
+      <input name="in2" type="float" value="2" />
+    </multiply>
+    <multiply name="NdotV_N_2" type="vector3">
+      <input name="in1" type="vector3" nodename="unit_normal" />
+      <input name="in2" type="float" nodename="NdotV_2" />
+    </multiply>
+    <subtract name="view_reflect" type="vector3">
+      <input name="in1" type="vector3" nodename="unit_viewdir" />
+      <input name="in2" type="vector3" nodename="NdotV_N_2" />
+    </subtract>
+    <multiply name="invert_lightdir" type="vector3">
+      <input name="in1" type="vector3" nodename="unit_lightdir" />
+      <input name="in2" type="float" value="-1" />
+    </multiply>
+    <dotproduct name="VdotR" type="float">
+      <input name="in1" type="vector3" nodename="invert_lightdir" />
+      <input name="in2" type="vector3" nodename="view_reflect" />
+    </dotproduct>
+    <max name="VdotR_nonnegative" type="float">
+      <input name="in1" type="float" nodename="VdotR" />
+      <input name="in2" type="float" value="0" />
+    </max>
+    <power name="specular_highlight" type="float">
+      <input name="in1" type="float" nodename="VdotR_nonnegative" />
+      <input name="in2" type="float" interfacename="shininess" />
+    </power>
+    <multiply name="specular" type="float">
+      <input name="in1" type="float" nodename="specular_highlight" />
+      <input name="in2" type="float" interfacename="specular_intensity" />
+    </multiply>
+    <add name="final_color" type="color3">
+      <input name="in1" type="color3" nodename="diffuse" />
+      <input name="in2" type="float" nodename="specular" />
+    </add>
+    <output name="out" type="color3" nodename="final_color" />
+  </nodegraph>
+
 </materialx>

resources/Materials/TestSuite/nprlib/gooch_shade.mtlx

@@ -0,0 +1,30 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <gooch_shade name="default_gooch" type="color3">
+    <input name="warm_color" type="color3" value="0.8, 0.8, 0.7" />
+    <input name="cool_color" type="color3" value="0.3, 0.3, 0.8" />
+    <input name="specular_intensity" type="float" value="1" />
+    <input name="shininess" type="float" value="64" />
+  </gooch_shade>
+  <surface_unlit name="unlit_surface" type="surfaceshader">
+    <input name="emission_color" type="color3" nodename="default_gooch" />
+  </surface_unlit>
+  <surfacematerial name="default_gooch_material" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="unlit_surface" />
+  </surfacematerial>
+
+  <gooch_shade name="red_blue_gooch" type="color3">
+    <input name="warm_color" type="color3" value="0.9, 0.1, 0.1" />
+    <input name="cool_color" type="color3" value="0.1, 0.1, 0.9" />
+    <input name="specular_intensity" type="float" value="1" />
+    <input name="shininess" type="float" value="64" />
+  </gooch_shade>
+  <surface_unlit name="redblue_gooch_surface" type="surfaceshader">
+    <input name="emission_color" type="color3" nodename="red_blue_gooch" />
+  </surface_unlit>
+  <surfacematerial name="redblue_gooch_material" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="redblue_gooch_surface" />
+  </surfacematerial>
+
+</materialx>