Fill the diffusion profile in the BSDFData

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.cs

 
             // SSS
             [SurfaceDataAttributes("Diffusion Profile")]
-            public int diffusionProfile;
+            public uint diffusionProfile;
             [SurfaceDataAttributes("Subsurface Mask")]
             public float subsurfaceMask;
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.cs.hlsl

     float3 normalWS;
     float perceptualRoughness;
     float coatMask;
-    int diffusionProfile;
+    uint diffusionProfile;
     float subsurfaceMask;
     float thickness;
     bool useThickObjectMode;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.hlsl

 }
 
 // Assume that bsdfData.diffusionProfile is init
-void FillMaterialSSS(float subsurfaceMask, inout BSDFData bsdfData)
+void FillMaterialSSS(uint diffusionProfile, float subsurfaceMask, inout BSDFData bsdfData)
-    bsdfData.fresnel0 = _TransmissionTintsAndFresnel0[bsdfData.diffusionProfile].a;
+    bsdfData.diffusionProfile = diffusionProfile;
+    bsdfData.fresnel0 = _TransmissionTintsAndFresnel0[diffusionProfile].a;
-void FillMaterialTransmission(float thickness, inout BSDFData bsdfData)
+void FillMaterialTransmission(uint diffusionProfile, float thickness, inout BSDFData bsdfData)
-    int diffusionProfile = bsdfData.diffusionProfile;
+    bsdfData.diffusionProfile = diffusionProfile;
 
     bsdfData.thickness = _ThicknessRemaps[diffusionProfile].x + _ThicknessRemaps[diffusionProfile].y * thickness;
     uint transmissionMode = BitFieldExtract(asuint(_TransmissionFlags), 2u * diffusionProfile, 2u);
     bsdfData.diffuseColor = ComputeDiffuseColor(surfaceData.baseColor, metallic);
     bsdfData.fresnel0     = HasFeatureFlag(surfaceData.materialFeatures, MATERIALFEATUREFLAGS_LIT_SPECULAR_COLOR) ? surfaceData.specularColor : ComputeFresnel0(surfaceData.baseColor, surfaceData.metallic, DEFAULT_SPECULAR_VALUE);
 
-    // Always assign even if not used, DIFFUSION_PROFILE_NEUTRAL_ID is 0
-    bsdfData.diffusionProfile = surfaceData.diffusionProfile;
+    // Note: DIFFUSION_PROFILE_NEUTRAL_ID is 0
 
     // In forward everything is statically know and we could theorically cumulate all the material features. So the code reflect it.
     // However in practice we keep parity between deferred and forward, so we should contrain the various features.
     {
         // Modify fresnel0
-        FillMaterialSSS(surfaceData.subsurfaceMask, bsdfData);
+        FillMaterialSSS(surfaceData.diffusionProfile, surfaceData.subsurfaceMask, bsdfData);
-        FillMaterialTransmission(surfaceData.thickness, bsdfData);
+        FillMaterialTransmission(surfaceData.diffusionProfile, surfaceData.thickness, bsdfData);
     }
 
     if (HasFeatureFlag(surfaceData.materialFeatures, MATERIALFEATUREFLAGS_LIT_ANISOTROPY))
         if (HasFeatureFlag(pixelFeatureFlags, MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING))
         {
             // Overwrite fresnel0
-            FillMaterialSSS(sssData.subsurfaceMask, bsdfData);
+            FillMaterialSSS(sssData.diffusionProfile, sssData.subsurfaceMask, bsdfData);
-            FillMaterialTransmission(inGBuffer2.g, bsdfData);
+            FillMaterialTransmission(sssData.diffusionProfile, inGBuffer2.g, bsdfData);
         }
     }