Add blackbody PBR node implementations (#1367)

Address the missing targets for the PBR blackbody node implementation using the following approximation: Wikipedia: Planckian Locus Approximation Add a simple unlit surface material example using the above blackbody node for emission. Reenable blackbody node tests.
AcademySoftwareFoundation · Jul 12, 2023 · 3e838e2 · 3e838e2
1 parent 2c0c7ea
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Showing 13 changed files with 129 additions and 6 deletions.
diff --git a/libraries/pbrlib/genglsl/mx_blackbody.glsl b/libraries/pbrlib/genglsl/mx_blackbody.glsl
@@ -0,0 +1,48 @@
+/// XYZ to Rec.709 RGB colorspace conversion
+const mat3 XYZ_to_RGB = mat3( 3.2406, -0.9689, 0.0557,
+                             -1.5372, 1.8758, -0.2040,
+                             -0.4986, 0.0415, 1.0570);
+
+void mx_blackbody(float temperatureKelvin, out vec3 colorValue)
+{
+    float xc, yc;
+    float t, t2, t3, xc2, xc3;
+
+    // if value outside valid range of approximation clamp to accepted temperature range
+    temperatureKelvin = clamp(temperatureKelvin, 1667.0, 25000.0);
+
+    t = 1000.0 / temperatureKelvin;
+    t2 = t * t;
+    t3 = t * t * t;
+
+    // Cubic spline approximation for Kelvin temperature to sRGB conversion
+    // (https://en.wikipedia.org/wiki/Planckian_locus#Approximation)
+    if (temperatureKelvin < 4000.0) {  // 1667K <= temperatureKelvin < 4000K
+      xc = -0.2661239 * t3 - 0.2343580 * t2 + 0.8776956 * t + 0.179910;
+    }
+    else {  // 4000K <= temperatureKelvin <= 25000K
+      xc = -3.0258469 * t3 + 2.1070379 * t2 + 0.2226347 * t + 0.240390;
+    }
+    xc2 = xc * xc;
+    xc3 = xc * xc * xc;
+
+    if (temperatureKelvin < 2222.0) {  // 1667K <= temperatureKelvin < 2222K
+      yc = -1.1063814 * xc3 - 1.34811020 * xc2 + 2.18555832 * xc - 0.20219683;
+    }
+    else if (temperatureKelvin < 4000.0) {  // 2222K <= temperatureKelvin < 4000K
+      yc = -0.9549476 * xc3 - 1.37418593 * xc2 + 2.09137015 * xc - 0.16748867;
+    }
+    else {  // 4000K <= temperatureKelvin <= 25000K
+      yc = 3.0817580 * xc3 - 5.87338670 * xc2 + 3.75112997 * xc - 0.37001483;
+    }
+
+    if (yc <= 0.0) {  // avoid division by zero
+      colorValue = vec3(1.0);
+      return;
+    }
+
+    vec3 XYZ = vec3(xc / yc, 1.0, (1.0 - xc - yc) / yc);
+
+    colorValue = XYZ_to_RGB * XYZ;
+    colorValue = max(colorValue, vec3(0.0));
+}
diff --git a/libraries/pbrlib/genglsl/pbrlib_genglsl_impl.mtlx b/libraries/pbrlib/genglsl/pbrlib_genglsl_impl.mtlx
@@ -74,4 +74,7 @@
   <!-- <artistic_ior> -->
   <implementation name="IM_artistic_ior_genglsl" nodedef="ND_artistic_ior" file="mx_artistic_ior.glsl" function="mx_artistic_ior" target="genglsl" />
 
+  <!-- <blackbody> -->
+  <implementation name="IM_blackbody_genglsl" nodedef="ND_blackbody" file="mx_blackbody.glsl" function="mx_blackbody" target="genglsl" />
+
 </materialx>
diff --git a/libraries/pbrlib/genmsl/pbrlib_genmsl_impl.mtlx b/libraries/pbrlib/genmsl/pbrlib_genmsl_impl.mtlx
@@ -71,4 +71,7 @@
   <!-- <artistic_ior> -->
   <implementation name="IM_artistic_ior_genmsl" nodedef="ND_artistic_ior" file="../genglsl/mx_artistic_ior.glsl" function="mx_artistic_ior" target="genmsl" />
 
+  <!-- <blackbody> -->
+  <implementation name="IM_blackbody_genmsl" nodedef="ND_blackbody" file="../genglsl/mx_blackbody.glsl" function="mx_blackbody" target="genmsl" />
+
 </materialx>
diff --git a/libraries/pbrlib/genosl/mx_blackbody.osl b/libraries/pbrlib/genosl/mx_blackbody.osl
@@ -0,0 +1,48 @@
+void mx_blackbody(float temperature, output color color_value)
+{
+    float xc, yc;
+    float t, t2, t3, xc2, xc3;
+
+    // if value outside valid range of approximation clamp to accepted temperature range
+    temperature = clamp(temperature, 1667.0, 25000.0);
+
+    t = 1000.0 / temperature;
+    t2 = t * t;
+    t3 = t * t * t;
+
+    // Cubic spline approximation for Kelvin temperature to sRGB conversion
+    // (https://en.wikipedia.org/wiki/Planckian_locus#Approximation)
+    if (temperature < 4000.0) {  // 1667K <= temperature < 4000K
+      xc = -0.2661239 * t3 - 0.2343580 * t2 + 0.8776956 * t + 0.179910;
+    }
+    else {  // 4000K <= temperature <= 25000K
+      xc = -3.0258469 * t3 + 2.1070379 * t2 + 0.2226347 * t + 0.240390;
+    }
+    xc2 = xc * xc;
+    xc3 = xc * xc * xc;
+
+    if (temperature < 2222.0) {  // 1667K <= temperature < 2222K
+      yc = -1.1063814 * xc3 - 1.34811020 * xc2 + 2.18555832 * xc - 0.20219683;
+    }
+    else if (temperature < 4000.0) {  // 2222K <= temperature < 4000K
+      yc = -0.9549476 * xc3 - 1.37418593 * xc2 + 2.09137015 * xc - 0.16748867;
+    }
+    else {  // 4000K <= temperature <= 25000K
+      yc = 3.0817580 * xc3 - 5.87338670 * xc2 + 3.75112997 * xc - 0.37001483;
+    }
+
+    if (yc <= 0.0) {  // avoid division by zero
+      color_value = color(1.0);
+      return;
+    }
+
+    vector XYZ = vector(xc / yc, 1.0, (1 - xc - yc) / yc);
+
+    /// XYZ to Rec.709 RGB colorspace conversion
+    matrix XYZ_to_RGB = matrix( 3.2406, -0.9689, 0.0557,
+                               -1.5372, 1.8758, -0.2040,
+                               -0.4986, 0.0415, 1.0570);
+
+    color_value = transform(XYZ_to_RGB, XYZ);
+    color_value = max(color_value, vector(0.0));
+}
diff --git a/libraries/pbrlib/genosl/pbrlib_genosl_impl.legacy b/libraries/pbrlib/genosl/pbrlib_genosl_impl.legacy
@@ -71,4 +71,7 @@
   <!-- <artistic_ior> -->
   <implementation name="IM_artistic_ior_genosl" nodedef="ND_artistic_ior" file="mx_artistic_ior.osl" function="mx_artistic_ior" target="genosl" />
 
+  <!-- <blackbody> -->
+  <implementation name="IM_blackbody_genosl" nodedef="ND_blackbody" file="mx_blackbody.osl" function="mx_blackbody" target="genosl" />
+
 </materialx>
diff --git a/libraries/pbrlib/genosl/pbrlib_genosl_impl.mtlx b/libraries/pbrlib/genosl/pbrlib_genosl_impl.mtlx
@@ -71,4 +71,7 @@
   <!-- <artistic_ior> -->
   <implementation name="IM_artistic_ior_genosl" nodedef="ND_artistic_ior" file="mx_artistic_ior.osl" function="mx_artistic_ior" target="genosl" />
 
+  <!-- <blackbody> -->
+  <implementation name="IM_blackbody_genosl" nodedef="ND_blackbody" file="mx_blackbody.osl" function="mx_blackbody" target="genosl" />
+
 </materialx>
diff --git a/resources/Materials/TestSuite/pbrlib/bsdf/blackbody.mtlx b/resources/Materials/TestSuite/pbrlib/bsdf/blackbody.mtlx
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <nodegraph name="NG_blackbody">
+    <input name="blackbody_temperature" type="float" value="5000.0" uimin="1500.0" uimax="25000.0" uistep="100.0" uiname="Blackbody Temperature Kelvin" />
+    <blackbody name="blackbody_color_out" type="color3">
+      <input name="temperature" type="float" interfacename="blackbody_temperature" />
+    </blackbody>
+    <output name="emission_color_output" type="color3" nodename="blackbody_color_out" />
+  </nodegraph>
+  <surface_unlit name="SR_blackbody" type="surfaceshader">
+    <input name="emission_color" type="color3" nodegraph="NG_blackbody" output="emission_color_output" />
+  </surface_unlit>
+  <surfacematerial name="Blackbody" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="SR_blackbody" />
+  </surfacematerial>
+</materialx>
diff --git a/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp b/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp
@@ -85,7 +85,7 @@ TEST_CASE("GenShader: GLSL Implementation Check", "[genglsl]")
 
     mx::StringSet generatorSkipNodeTypes;
     mx::StringSet generatorSkipNodeDefs;
-    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
+    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 47);
 }
 
 TEST_CASE("GenShader: GLSL Unique Names", "[genglsl]")

diff --git a/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp b/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp
@@ -93,7 +93,7 @@ TEST_CASE("GenShader: MDL Implementation Check", "[genmdl]")
     generatorSkipNodeTypes.insert("light");
     mx::StringSet generatorSkipNodeDefs;
 
-    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 49);
+    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
 }
 
 

diff --git a/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp b/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp
@@ -84,7 +84,7 @@ TEST_CASE("GenShader: MSL Implementation Check", "[genmsl]")
 
     mx::StringSet generatorSkipNodeTypes;
     mx::StringSet generatorSkipNodeDefs;
-    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
+    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 47);
 }
 
 TEST_CASE("GenShader: MSL Unique Names", "[genmsl]")

diff --git a/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp b/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp
@@ -89,7 +89,7 @@ TEST_CASE("GenShader: OSL Implementation Check", "[genosl]")
     generatorSkipNodeTypes.insert("light");
     mx::StringSet generatorSkipNodeDefs;
 
-    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 49);
+    GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
 }
 
 TEST_CASE("GenShader: OSL Unique Names", "[genosl]")

diff --git a/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp b/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp
@@ -94,7 +94,6 @@ void checkImplementations(mx::GenContext& context,
         "arrayappend",
         "displacement",
         "volume",
-        "blackbody",
         "curveadjust",
         "conical_edf",
         "measured_edf",

diff --git a/source/MaterialXView/Editor.cpp b/source/MaterialXView/Editor.cpp
@@ -701,7 +701,7 @@ ng::FloatBox<float>* createFloatWidget(ng::Widget* parent, const std::string& la
 
     if (ui)
     {
-        std::pair<float, float> range(0.0f, 0.0f);
+        std::pair<float, float> range(0.0f, 1.0f);
         if (ui->uiMin)
         {
             box->set_min_value(ui->uiMin->asA<float>());