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nicolassavva-autodesknicolassavva-autodesk
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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.
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13 files changed

Lines changed: 129 additions & 6 deletions

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‎libraries/pbrlib/genglsl/mx_blackbody.glsl‎

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/// XYZ to Rec.709 RGB colorspace conversion
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const mat3 XYZ_to_RGB = mat3( 3.2406, -0.9689, 0.0557,
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-1.5372, 1.8758, -0.2040,
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-0.4986, 0.0415, 1.0570);
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void mx_blackbody(float temperatureKelvin, out vec3 colorValue)
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{
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float xc, yc;
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float t, t2, t3, xc2, xc3;
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// if value outside valid range of approximation clamp to accepted temperature range
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temperatureKelvin = clamp(temperatureKelvin, 1667.0, 25000.0);
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t = 1000.0 / temperatureKelvin;
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t2 = t * t;
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t3 = t * t * t;
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// Cubic spline approximation for Kelvin temperature to sRGB conversion
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// (https://en.wikipedia.org/wiki/Planckian_locus#Approximation)
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if (temperatureKelvin < 4000.0) { // 1667K <= temperatureKelvin < 4000K
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xc = -0.2661239 * t3 - 0.2343580 * t2 + 0.8776956 * t + 0.179910;
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}
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else { // 4000K <= temperatureKelvin <= 25000K
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xc = -3.0258469 * t3 + 2.1070379 * t2 + 0.2226347 * t + 0.240390;
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}
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xc2 = xc * xc;
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xc3 = xc * xc * xc;
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if (temperatureKelvin < 2222.0) { // 1667K <= temperatureKelvin < 2222K
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yc = -1.1063814 * xc3 - 1.34811020 * xc2 + 2.18555832 * xc - 0.20219683;
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}
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else if (temperatureKelvin < 4000.0) { // 2222K <= temperatureKelvin < 4000K
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yc = -0.9549476 * xc3 - 1.37418593 * xc2 + 2.09137015 * xc - 0.16748867;
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}
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else { // 4000K <= temperatureKelvin <= 25000K
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yc = 3.0817580 * xc3 - 5.87338670 * xc2 + 3.75112997 * xc - 0.37001483;
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}
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if (yc <= 0.0) { // avoid division by zero
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colorValue = vec3(1.0);
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return;
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}
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vec3 XYZ = vec3(xc / yc, 1.0, (1.0 - xc - yc) / yc);
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colorValue = XYZ_to_RGB * XYZ;
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colorValue = max(colorValue, vec3(0.0));
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}

‎libraries/pbrlib/genglsl/pbrlib_genglsl_impl.mtlx‎

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<!-- <artistic_ior> -->
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<implementation name="IM_artistic_ior_genglsl" nodedef="ND_artistic_ior" file="mx_artistic_ior.glsl" function="mx_artistic_ior" target="genglsl" />
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<!-- <blackbody> -->
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<implementation name="IM_blackbody_genglsl" nodedef="ND_blackbody" file="mx_blackbody.glsl" function="mx_blackbody" target="genglsl" />
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</materialx>

‎libraries/pbrlib/genmsl/pbrlib_genmsl_impl.mtlx‎

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<!-- <artistic_ior> -->
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<implementation name="IM_artistic_ior_genmsl" nodedef="ND_artistic_ior" file="../genglsl/mx_artistic_ior.glsl" function="mx_artistic_ior" target="genmsl" />
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<!-- <blackbody> -->
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<implementation name="IM_blackbody_genmsl" nodedef="ND_blackbody" file="../genglsl/mx_blackbody.glsl" function="mx_blackbody" target="genmsl" />
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</materialx>

‎libraries/pbrlib/genosl/mx_blackbody.osl‎

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void mx_blackbody(float temperature, output color color_value)
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{
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float xc, yc;
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float t, t2, t3, xc2, xc3;
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// if value outside valid range of approximation clamp to accepted temperature range
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temperature = clamp(temperature, 1667.0, 25000.0);
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t = 1000.0 / temperature;
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t2 = t * t;
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t3 = t * t * t;
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// Cubic spline approximation for Kelvin temperature to sRGB conversion
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// (https://en.wikipedia.org/wiki/Planckian_locus#Approximation)
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if (temperature < 4000.0) { // 1667K <= temperature < 4000K
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xc = -0.2661239 * t3 - 0.2343580 * t2 + 0.8776956 * t + 0.179910;
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}
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else { // 4000K <= temperature <= 25000K
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xc = -3.0258469 * t3 + 2.1070379 * t2 + 0.2226347 * t + 0.240390;
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}
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xc2 = xc * xc;
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xc3 = xc * xc * xc;
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if (temperature < 2222.0) { // 1667K <= temperature < 2222K
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yc = -1.1063814 * xc3 - 1.34811020 * xc2 + 2.18555832 * xc - 0.20219683;
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}
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else if (temperature < 4000.0) { // 2222K <= temperature < 4000K
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yc = -0.9549476 * xc3 - 1.37418593 * xc2 + 2.09137015 * xc - 0.16748867;
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}
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else { // 4000K <= temperature <= 25000K
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yc = 3.0817580 * xc3 - 5.87338670 * xc2 + 3.75112997 * xc - 0.37001483;
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}
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if (yc <= 0.0) { // avoid division by zero
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color_value = color(1.0);
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return;
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}
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vector XYZ = vector(xc / yc, 1.0, (1 - xc - yc) / yc);
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/// XYZ to Rec.709 RGB colorspace conversion
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matrix XYZ_to_RGB = matrix( 3.2406, -0.9689, 0.0557,
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-1.5372, 1.8758, -0.2040,
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-0.4986, 0.0415, 1.0570);
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color_value = transform(XYZ_to_RGB, XYZ);
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color_value = max(color_value, vector(0.0));
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}

‎libraries/pbrlib/genosl/pbrlib_genosl_impl.legacy‎

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<!-- <artistic_ior> -->
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<implementation name="IM_artistic_ior_genosl" nodedef="ND_artistic_ior" file="mx_artistic_ior.osl" function="mx_artistic_ior" target="genosl" />
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<!-- <blackbody> -->
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<implementation name="IM_blackbody_genosl" nodedef="ND_blackbody" file="mx_blackbody.osl" function="mx_blackbody" target="genosl" />
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</materialx>

‎libraries/pbrlib/genosl/pbrlib_genosl_impl.mtlx‎

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<!-- <artistic_ior> -->
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<implementation name="IM_artistic_ior_genosl" nodedef="ND_artistic_ior" file="mx_artistic_ior.osl" function="mx_artistic_ior" target="genosl" />
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<!-- <blackbody> -->
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<implementation name="IM_blackbody_genosl" nodedef="ND_blackbody" file="mx_blackbody.osl" function="mx_blackbody" target="genosl" />
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</materialx>

‎resources/Materials/TestSuite/pbrlib/bsdf/blackbody.mtlx‎

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<?xml version="1.0"?>
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<materialx version="1.38" colorspace="lin_rec709">
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<nodegraph name="NG_blackbody">
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<input name="blackbody_temperature" type="float" value="5000.0" uimin="1500.0" uimax="25000.0" uistep="100.0" uiname="Blackbody Temperature Kelvin" />
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<blackbody name="blackbody_color_out" type="color3">
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<input name="temperature" type="float" interfacename="blackbody_temperature" />
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</blackbody>
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<output name="emission_color_output" type="color3" nodename="blackbody_color_out" />
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</nodegraph>
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<surface_unlit name="SR_blackbody" type="surfaceshader">
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<input name="emission_color" type="color3" nodegraph="NG_blackbody" output="emission_color_output" />
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</surface_unlit>
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<surfacematerial name="Blackbody" type="material">
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<input name="surfaceshader" type="surfaceshader" nodename="SR_blackbody" />
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</surfacematerial>
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</materialx>

‎source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp‎

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mx::StringSet generatorSkipNodeTypes;
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mx::StringSet generatorSkipNodeDefs;
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 47);
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}
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TEST_CASE("GenShader: GLSL Unique Names", "[genglsl]")

‎source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp‎

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generatorSkipNodeTypes.insert("light");
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mx::StringSet generatorSkipNodeDefs;
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 49);
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
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}
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‎source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp‎

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mx::StringSet generatorSkipNodeTypes;
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mx::StringSet generatorSkipNodeDefs;
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 48);
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GenShaderUtil::checkImplementations(context, generatorSkipNodeTypes, generatorSkipNodeDefs, 47);
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}
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TEST_CASE("GenShader: MSL Unique Names", "[genmsl]")

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