Principled material: parameter specularMetallic

CHANGELOG.md

@@ -12,6 +12,9 @@ Version History
       of the first *non-specular* hit for denoising)
     - Channel `OSP_FB_POSITION` holds the world-space position of the first hit
 -   Improved sampling of layered materials
+-   New parameter `specularMetallic` for the Principled material to
+    optionally disable the incluence of `specular` to metallicness,
+    improving compatibility with glTF `KHR_materials_specular`
 
 ### Changes in v3.2.0:
 

doc/api.md

@@ -1977,6 +1977,8 @@ listed in the table below.
 
   float  specular                   1  specular reflection/transmission weight in [0–1]
 
+  bool   specularMetallic        true  whether specular influences metallic
+
   float  ior                        1  dielectric index of refraction
 
   float  transmission               0  specular transmission weight in [0–1]

modules/cpu/render/materials/Principled.cpp

@@ -39,6 +39,7 @@ void Principled::commit()
   metallic = getMaterialParam1f("metallic", 0.f);
   diffuse = getMaterialParam1f("diffuse", 1.f);
   specular = getMaterialParam1f("specular", 1.f);
+  bool specularMetallic = getParam<bool>("specularMetallic", true);
   ior = getMaterialParam1f("ior", 1.f);
   transmission = getMaterialParam1f("transmission", 0.f);
   transmissionColor = getMaterialParam3f("transmissionColor", vec3f(1.f));
@@ -88,6 +89,7 @@ void Principled::commit()
   getSh()->diffuse = diffuse.factor;
   getSh()->diffuseMap = diffuse.tex;
   getSh()->specular = specular.factor;
+  getSh()->specularMetallic = specularMetallic;
   getSh()->specularMap = specular.tex;
   getSh()->ior = ior.factor;
   getSh()->iorMap = ior.tex;

modules/cpu/render/materials/Principled.ispc

@@ -308,7 +308,8 @@ SYCL_EXTERNAL const varying BSDF *uniform Principled_getBSDF(
     }
 
     // conductor base
-    const float conductor = metallic * specular;
+    const float conductor =
+        metallic * (self->specularMetallic ? specular : 1.0f);
     if (conductor > EPS) {
       const vec3f edgeColor = clamp(
           self->edgeColor * get3f(self->edgeColorMap, dg, make_vec3f(1.f)));

modules/cpu/render/materials/PrincipledShared.h

@@ -32,6 +32,7 @@ struct Principled
   // specular weight in [0, 1]
   float specular;
   TextureParam specularMap;
+  bool specularMetallic;
 
   // index of refraction
   float ior;
@@ -132,6 +133,7 @@ struct Principled
         metallic(0.f),
         diffuse(1.f),
         specular(1.f),
+        specularMetallic(true),
         ior(1.f),
         transmission(0.f),
         transmissionColor(1.f),