AcademySoftwareFoundation · msuzuki-nvidia · Feb 20, 2026 · Feb 20, 2026 · Feb 20, 2026 · Feb 23, 2026
diff --git a/.gitignore b/.gitignore
@@ -1,3 +1,4 @@
 build
 dist
 .DS_Store
+CMakeUserPresets.json
diff --git a/documents/Specification/MaterialX.PBRSpec.md b/documents/Specification/MaterialX.PBRSpec.md
@@ -200,16 +200,19 @@ Implementations are expected to preserve energy as the roughness of the surface
 
 The `tint` input colors the reflected and transmitted light but should be left at white (1,1,1) for physically correct results. Setting the `ior` input to zero disables the Fresnel curve, allowing reflectivity to be controlled purely by weight and tint.
 
-The `scatter_mode` controls whether the surface reflects light (`R`), transmits light (`T`), or both (`RT`). In `RT` mode, reflection and transmission occur both when entering and leaving a surface, with their respective intensities controlled by the Fresnel curve. Depending on the IOR and incident angle, total internal reflection may occur even when transmission modes are selected.
+Setting `retroreflective` to true switches the BSDF to retroreflection mode, where light is reflected back toward the incoming direction rather than the mirror reflection direction[^Raab2025].
 
 Thin-film iridescence effects[^Belcour2017] may be enabled by setting `thinfilm_thickness` to a non-zero value.
 
+The `scatter_mode` controls whether the surface reflects light (`R`), transmits light (`T`), or both (`RT`). In `RT` mode, reflection and transmission occur both when entering and leaving a surface, with their respective intensities controlled by the Fresnel curve. Depending on the IOR and incident angle, total internal reflection may occur even when transmission modes are selected.
+
 |Port                |Description                                                    |Type   |Default      |Accepted Values|
 |--------------------|---------------------------------------------------------------|-------|-------------|---------------|
 |`weight`            |Weight of the BSDF contribution                                |float  |1.0          |[0, 1]         |
 |`tint`              |Color weight to tint the reflected and transmitted light       |color3 |1.0, 1.0, 1.0|               |
 |`ior`               |Index of refraction of the surface                             |float  |1.5          |               |
 |`roughness`         |Surface roughness along the tangent and bitangent              |vector2|0.05, 0.05   |[0, 1]         |
+|`retroeflective`    |Enable retroreflection mode for the BSDF                       |boolean|false        |               |
 |`thinfilm_thickness`|Thickness of the iridescent thin-film layer in nanometers      |float  |0.0          |               |
 |`thinfilm_ior`      |Index of refraction of the thin-film layer                     |float  |1.5          |               |
 |`normal`            |Normal vector of the surface                                   |vector3|Nworld       |               |
@@ -227,6 +230,8 @@ Implementations are expected to preserve energy as the roughness of the surface
 
 The default values for `ior` and `extinction` represent approximate values for gold.
 
+Setting `retroreflective` to true switches the BSDF to retroreflection mode, where light is reflected back toward the incoming direction rather than the mirror reflection direction[^Raab2025].
+
 Thin-film iridescence effects[^Belcour2017] may be enabled by setting `thinfilm_thickness` to a non-zero value.
 
 |Port                |Description                                              |Type   |Default               |Accepted Values|
@@ -235,6 +240,7 @@ Thin-film iridescence effects[^Belcour2017] may be enabled by setting `thinfilm_
 |`ior`               |Index of refraction                                      |color3 |0.183, 0.421, 1.373   |               |
 |`extinction`        |Extinction coefficient                                   |color3 |3.424, 2.346, 1.770   |               |
 |`roughness`         |Surface roughness                                        |vector2|0.05, 0.05            |[0, 1]         |
+|`retroreflective`   |Enable retroreflection mode for the BSDF                 |boolean|false                 |               |
 |`thinfilm_thickness`|Thickness of the iridescent thin-film layer in nanometers|float  |0.0                   |               |
 |`thinfilm_ior`      |Index of refraction of the thin-film layer               |float  |1.5                   |               |
 |`normal`            |Normal vector of the surface                             |vector3|Nworld                |               |
@@ -251,10 +257,12 @@ Implementations are expected to preserve energy as the roughness of the surface
 
 The `color82` input provides a multiplier on reflectivity at 82 degrees, useful for capturing the characteristic "dip" in the reflectance curve of metallic surfaces. Setting it to (1,1,1) effectively disables this feature for backward compatibility.
 
-The `scatter_mode` behavior matches that of `dielectric_bsdf`: in `RT` mode, reflection and transmission occur both when entering and leaving a surface, with intensities controlled by the Fresnel curve. Total internal reflection may occur depending on the incident angle.
+Setting `retroreflective` to true switches the BSDF to retroreflection mode, where light is reflected back toward the incoming direction rather than the mirror reflection direction[^Raab2025].
 
 Thin-film iridescence effects[^Belcour2017] may be enabled by setting `thinfilm_thickness` to a non-zero value.
 
+The `scatter_mode` behavior matches that of `dielectric_bsdf`: in `RT` mode, reflection and transmission occur both when entering and leaving a surface, with intensities controlled by the Fresnel curve. Total internal reflection may occur depending on the incident angle.
+
 |Port                |Description                                                    |Type   |Default      |Accepted Values|
 |--------------------|---------------------------------------------------------------|-------|-------------|---------------|
 |`weight`            |Weight of the BSDF contribution                                |float  |1.0          |[0, 1]         |
@@ -263,6 +271,7 @@ Thin-film iridescence effects[^Belcour2017] may be enabled by setting `thinfilm_
 |`color90`           |Reflectivity per color component at grazing angles             |color3 |1.0, 1.0, 1.0|               |
 |`exponent`          |Exponent for Schlick blending between color0 and color90       |float  |5.0          |               |
 |`roughness`         |Surface roughness along the tangent and bitangent              |vector2|0.05, 0.05   |[0, 1]         |
+|`retroreflective`   |Enable retroreflection mode for the BSDF                       |boolean|false        |               |
 |`thinfilm_thickness`|Thickness of the iridescent thin-film layer in nanometers      |float  |0.0          |               |
 |`thinfilm_ior`      |Index of refraction of the thin-film layer                     |float  |1.5          |               |
 |`normal`            |Normal vector of the surface                                   |vector3|Nworld       |               |
@@ -702,6 +711,8 @@ Path Tracing**, <https://media.disneyanimation.com/uploads/production/publicatio
 
 [^Portsmouth2025]: Portsmouth et al., **EON: A practical energy-preserving rough diffuse BRDF**, <https://www.jcgt.org/published/0014/01/06/>, 2025.
 
+[^Raab2025]: Matthias Raab et al., **The Minimal Retroreflective Microfacet Model**, to appear, 2025
+
 [^Turquin2019]: Emmanuel Turquin, **Practical multiple scattering compensation for microfacet models**, <https://blog.selfshadow.com/publications/turquin/ms_comp_final.pdf>, 2019.
 
 [^Walter2007]: Bruce Walter et al., **Microfacet Models for Refraction through Rough Surfaces**, <https://www.graphics.cornell.edu/~bjw/microfacetbsdf.pdf>, 2007

diff --git a/libraries/pbrlib/genglsl/mx_conductor_bsdf.glsl b/libraries/pbrlib/genglsl/mx_conductor_bsdf.glsl
@@ -1,7 +1,7 @@
 #include "lib/mx_closure_type.glsl"
 #include "lib/mx_microfacet_specular.glsl"
 
-void mx_conductor_bsdf(ClosureData closureData, float weight, vec3 ior_n, vec3 ior_k, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, inout BSDF bsdf)
+void mx_conductor_bsdf(ClosureData closureData, float weight, vec3 ior_n, vec3 ior_k, vec2 roughness, bool retroreflective, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, inout BSDF bsdf)
 {
     bsdf.throughput = vec3(0.0);
 
@@ -13,6 +13,7 @@ void mx_conductor_bsdf(ClosureData closureData, float weight, vec3 ior_n, vec3 i
     vec3 V = closureData.V;
     vec3 L = closureData.L;
 
+    V = retroreflective ? reflect(-V, N) : V;
     N = mx_forward_facing_normal(N, V);
     float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
 

diff --git a/libraries/pbrlib/genglsl/mx_dielectric_bsdf.glsl b/libraries/pbrlib/genglsl/mx_dielectric_bsdf.glsl
@@ -1,7 +1,7 @@
 #include "lib/mx_closure_type.glsl"
 #include "lib/mx_microfacet_specular.glsl"
 
-void mx_dielectric_bsdf(ClosureData closureData, float weight, vec3 tint, float ior, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+void mx_dielectric_bsdf(ClosureData closureData, float weight, vec3 tint, float ior, vec2 roughness, bool retroreflective, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
 {
     if (weight < M_FLOAT_EPS)
     {
@@ -15,6 +15,10 @@ void mx_dielectric_bsdf(ClosureData closureData, float weight, vec3 tint, float
     vec3 V = closureData.V;
     vec3 L = closureData.L;
 
+    // Retroreflective mode is only supported for reflection and indirect
+    if (retroreflective && (closureData.closureType != CLOSURE_TYPE_TRANSMISSION))
+        V = reflect(-V, N);
+
     N = mx_forward_facing_normal(N, V);
     float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
 

diff --git a/libraries/pbrlib/genglsl/mx_generalized_schlick_bsdf.glsl b/libraries/pbrlib/genglsl/mx_generalized_schlick_bsdf.glsl
@@ -1,7 +1,7 @@
 #include "lib/mx_closure_type.glsl"
 #include "lib/mx_microfacet_specular.glsl"
 
-void mx_generalized_schlick_bsdf(ClosureData closureData, float weight, vec3 color0, vec3 color82, vec3 color90, float exponent, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+void mx_generalized_schlick_bsdf(ClosureData closureData, float weight, vec3 color0, vec3 color82, vec3 color90, float exponent, vec2 roughness, bool retroreflective, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
 {
     if (weight < M_FLOAT_EPS)
     {
@@ -15,6 +15,10 @@ void mx_generalized_schlick_bsdf(ClosureData closureData, float weight, vec3 col
     vec3 V = closureData.V;
     vec3 L = closureData.L;
 
+    // Retroreflective mode is only supported for reflection and indirect
+    if (retroreflective && (closureData.closureType != CLOSURE_TYPE_TRANSMISSION))
+        V = reflect(-V, N);
+
     N = mx_forward_facing_normal(N, V);
     float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
 

diff --git a/libraries/pbrlib/genmdl/pbrlib_genmdl_impl.mtlx b/libraries/pbrlib/genmdl/pbrlib_genmdl_impl.mtlx
@@ -11,13 +11,13 @@
   <implementation name="IM_translucent_bsdf_genmdl" nodedef="ND_translucent_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_translucent_bsdf(mxp_weight:{{weight}}, mxp_color:{{color}}, mxp_normal:{{normal}})" target="genmdl" />
 
   <!-- <dielectric_bsdf> -->
-  <implementation name="IM_dielectric_bsdf_genmdl" nodedef="ND_dielectric_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_dielectric_bsdf(mxp_weight:{{weight}}, mxp_tint:{{tint}}, mxp_ior:{{ior}}, mxp_roughness:{{roughness}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}}, mxp_top_weight:{{top_weight}})" target="genmdl" />
+  <implementation name="IM_dielectric_bsdf_genmdl" nodedef="ND_dielectric_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_dielectric_bsdf(mxp_weight:{{weight}}, mxp_tint:{{tint}}, mxp_ior:{{ior}}, mxp_roughness:{{roughness}}, mxp_retroreflective:{{retroreflective}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}}, mxp_top_weight:{{top_weight}})" target="genmdl" />
 
   <!-- <conductor_bsdf> -->
-  <implementation name="IM_conductor_bsdf_genmdl" nodedef="ND_conductor_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_conductor_bsdf(mxp_weight:{{weight}}, mxp_ior:{{ior}}, mxp_extinction:{{extinction}}, mxp_roughness:{{roughness}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}})" target="genmdl" />
+  <implementation name="IM_conductor_bsdf_genmdl" nodedef="ND_conductor_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_conductor_bsdf(mxp_weight:{{weight}}, mxp_ior:{{ior}}, mxp_extinction:{{extinction}}, mxp_roughness:{{roughness}}, mxp_retroreflective:{{retroreflective}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}})" target="genmdl" />
 
   <!-- <generalized_schlick_bsdf> -->
-  <implementation name="IM_generalized_schlick_bsdf_genmdl" nodedef="ND_generalized_schlick_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_generalized_schlick_bsdf(mxp_weight:{{weight}}, mxp_color0:{{color0}}, mxp_color82:{{color82}}, mxp_color90:{{color90}}, mxp_exponent:{{exponent}},mxp_roughness:{{roughness}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}}, mxp_top_weight:{{top_weight}})" target="genmdl" />
+  <implementation name="IM_generalized_schlick_bsdf_genmdl" nodedef="ND_generalized_schlick_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_generalized_schlick_bsdf(mxp_weight:{{weight}}, mxp_color0:{{color0}}, mxp_color82:{{color82}}, mxp_color90:{{color90}}, mxp_exponent:{{exponent}},mxp_roughness:{{roughness}}, mxp_retroreflective:{{retroreflective}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}}, mxp_top_weight:{{top_weight}})" target="genmdl" />
 
   <!-- <subsurface_bsdf> -->
   <implementation name="IM_subsurface_bsdf_genmdl" nodedef="ND_subsurface_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_subsurface_bsdf(mxp_weight:{{weight}}, mxp_color:{{color}}, mxp_radius:{{radius}}, mxp_anisotropy:{{anisotropy}}, mxp_normal:{{normal}})" target="genmdl" />

diff --git a/libraries/pbrlib/genosl/mx_dielectric_bsdf.osl b/libraries/pbrlib/genosl/mx_dielectric_bsdf.osl
@@ -1,4 +1,4 @@
-void mx_dielectric_bsdf(float weight, color tint, float ior, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+void mx_dielectric_bsdf(float weight, color tint, float ior, vector2 roughness, int retroreflective, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
 {
     color reflection_tint = (scatter_mode == "T") ? color(0.0) : tint;
     color transmission_tint = (scatter_mode == "R") ? color(0.0) : tint;

diff --git a/libraries/pbrlib/genosl/mx_generalized_schlick_bsdf.osl b/libraries/pbrlib/genosl/mx_generalized_schlick_bsdf.osl
@@ -1,4 +1,4 @@
-void mx_generalized_schlick_bsdf(float weight, color color0, color color82, color color90, float exponent, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+void mx_generalized_schlick_bsdf(float weight, color color0, color color82, color color90, float exponent, vector2 roughness, int retroreflective, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
 {
     color reflection_tint = (scatter_mode == "T") ? color(0.0) : color(1.0);
     color transmission_tint = (scatter_mode == "R") ? color(0.0) : color(1.0);

diff --git a/libraries/pbrlib/pbrlib_defs.mtlx b/libraries/pbrlib/pbrlib_defs.mtlx
@@ -64,6 +64,7 @@
     <input name="tint" type="color3" value="1.0, 1.0, 1.0" />
     <input name="ior" type="float" value="1.5" />
     <input name="roughness" type="vector2" value="0.05, 0.05" />
+    <input name="retroreflective" type="boolean" value="false" uniform="true" />
     <input name="thinfilm_thickness" type="float" value="0" unittype="distance" unit="nanometer" />
     <input name="thinfilm_ior" type="float" value="1.5" />
     <input name="normal" type="vector3" defaultgeomprop="Nworld" />
@@ -82,6 +83,7 @@
     <input name="ior" type="color3" value="0.183, 0.421, 1.373" />
     <input name="extinction" type="color3" value="3.424, 2.346, 1.770" />
     <input name="roughness" type="vector2" value="0.05, 0.05" />
+    <input name="retroreflective" type="boolean" value="false" uniform="true" />
     <input name="thinfilm_thickness" type="float" value="0" unittype="distance" unit="nanometer" />
     <input name="thinfilm_ior" type="float" value="1.5" />
     <input name="normal" type="vector3" defaultgeomprop="Nworld" />
@@ -101,6 +103,7 @@
     <input name="color90" type="color3" value="1.0, 1.0, 1.0" />
     <input name="exponent" type="float" value="5.0" />
     <input name="roughness" type="vector2" value="0.05, 0.05" />
+    <input name="retroreflective" type="boolean" value="false" uniform="true" />
     <input name="thinfilm_thickness" type="float" value="0" unittype="distance" unit="nanometer" />
     <input name="thinfilm_ior" type="float" value="1.5" />
     <input name="normal" type="vector3" defaultgeomprop="Nworld" />

diff --git a/resources/Materials/TestSuite/pbrlib/bsdf/conductor.mtlx b/resources/Materials/TestSuite/pbrlib/bsdf/conductor.mtlx
@@ -7,6 +7,7 @@
     </roughness_anisotropy>
     <conductor_bsdf name="conductor_brdf1" type="BSDF">
       <input name="roughness" type="vector2" nodename="roughness1" />
+      <input name="retroreflective" type="boolean" value="false" />
       <input name="ior" type="color3" nodename="conductor_brdf1__artistic_ior" output="ior" />
       <input name="extinction" type="color3" nodename="conductor_brdf1__artistic_ior" output="extinction" />
     </conductor_bsdf>

diff --git a/resources/Materials/TestSuite/pbrlib/bsdf/dielectric.mtlx b/resources/Materials/TestSuite/pbrlib/bsdf/dielectric.mtlx
@@ -4,6 +4,7 @@
     <dielectric_bsdf name="dielectric_R" type="BSDF">
       <input name="weight" type="float" value="1.0" />
       <input name="tint" type="color3" value="0.7, 0.7, 0.7" />
+      <input name="retroreflective" type="boolean" value="false" />
       <input name="scatter_mode" type="string" value="R" />
     </dielectric_bsdf>
     <surface name="surface_R" type="surfaceshader">

diff --git a/resources/Materials/TestSuite/pbrlib/bsdf/generalized_schlick.mtlx b/resources/Materials/TestSuite/pbrlib/bsdf/generalized_schlick.mtlx
@@ -4,6 +4,7 @@
     <generalized_schlick_bsdf name="schlick_R" type="BSDF">
       <input name="color0" type="color3" value="0.8, 0.8, 0.8" />
       <input name="roughness" type="vector2" value="0.02, 0.02" />
+      <input name="retroreflective" type="boolean" value="false" />
       <input name="scatter_mode" type="string" value="R" />
     </generalized_schlick_bsdf>
     <surface name="surface_R" type="surfaceshader">

diff --git a/source/MaterialXFormat/File.cpp b/source/MaterialXFormat/File.cpp
@@ -280,6 +280,17 @@ FilePathVec FilePath::getSubDirectories() const
 
 void FilePath::createDirectory() const
 {
+    if (isEmpty() || exists())
+    {
+        return;
+    }
+
+    FilePath parent = getParentPath();
+    if (!parent.isEmpty() && !parent.exists())
+    {
+        parent.createDirectory();
+    }
+
 #if defined(_WIN32)
     _mkdir(asString().c_str());
 #else

diff --git a/source/MaterialXGenMdl/mdl/materialx/pbrlib_1_10.mdl b/source/MaterialXGenMdl/mdl/materialx/pbrlib_1_10.mdl
@@ -165,6 +165,7 @@ export material mx_generalized_schlick_bsdf(
     color  mxp_color90   = color(1.0),
     float  mxp_exponent  = 5.0,
     float2 mxp_roughness = float2(0.05),
+    uniform bool mxp_retroreflective = false [[ anno::unused() ]],
     float3 mxp_normal    = state::normal(),
     float3 mxp_tangent   = state::texture_tangent_u(0),
     uniform core::mx_distribution_type mxp_distribution = core::mx_distribution_type_ggx [[ anno::unused() ]],