[8.x.x Backport] Fixed an issue with the specularFGD term being used when the material has a clear coat (lit shader).

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -78,6 +78,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix for issue that prevented scene from being completely saved when baked reflection probes are present and lighting is set to auto generate.
 - Fixed the depth buffer copy made before custom pass after opaque and normal injection point.
 - Fixed a weird behavior in the scalable settings drawing when the space becomes tiny (1212045).
+- Fixed an issue with the specularFGD term being used when the material has a clear coat (lit shader).
 
 ### Changed
 - Renamed the cubemap used for diffuse convolution to a more explicit name for the memory profiler.

com.unity.render-pipelines.high-definition/Runtime/Material/Lit/Lit.hlsl

@@ -1710,7 +1710,12 @@ IndirectLighting EvaluateBSDF_ScreenSpaceReflection(PositionInputs posInput,
     ApplyScreenSpaceReflectionWeight(ssrLighting);
 
     // TODO: we should multiply all indirect lighting by the FGD value only ONCE.
-    lighting.specularReflected = ssrLighting.rgb * preLightData.specularFGD;
+    // In case this material has a clear coat, we shou not be using the specularFGD. The condition for it is a combination
+    // of a materia feature and the coat mask.
+    float clampedNdotV = ClampNdotV(preLightData.NdotV);
+    lighting.specularReflected = ssrLighting.rgb * (HasFlag(bsdfData.materialFeatures, MATERIALFEATUREFLAGS_LIT_CLEAR_COAT) ? 
+                                                    lerp(preLightData.specularFGD, F_Schlick(CLEAR_COAT_F0, clampedNdotV), bsdfData.coatMask) 
+                                                    : preLightData.specularFGD);
     reflectionHierarchyWeight  = ssrLighting.a;
 
     return lighting;