[7.x.x Backport] Fixed an issue with the specularFGD term being used when the material has a clear coat (lit shader). (#21)

* Fixed an issue with the specularFGD term being used when the material has a clear coat (lit shader).

* update ssr screenshot

Co-authored-by: sebastienlagarde <[email protected]>

Author: anisunity

TestProjects/HDRP_Tests/Assets/ReferenceImages/Linear/WindowsEditor/Direct3D11/2551_SSR.png

@@ -41,6 +41,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed path validation when creating new volume profile (case 1229933)
 - Fixed various object leaks in HDRP.
 - Fix for assertion triggering sometimes when saving a newly created lit shader graph (case 1230996)
+- Fixed an issue with the specularFGD term being used when the material has a clear coat (lit shader).
 
 ### Changed
 - Rejecting history for ray traced reflections based on a threshold evaluated on the neighborhood of the sampled history.

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

@@ -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;