[HDRP] Remove Fake GTAO bounce on the occlusion when used for direct lighting

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

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed lens flare occlusion issues with TAA. (1365098)
 - Fixed misleading text and improving the eye scene material samples. (case 1368665)
 - Fixed missing DisallowMultipleComponent annotations in HDAdditionalReflectionData and HDAdditionalLightData (case 1365879).
+- Fixed ambient occlusion strenght incorrectly using GTAOMultiBounce
 
 ## [13.0.0] - 2021-09-01
 

com.unity.render-pipelines.high-definition/Documentation~/Upgrading-from-2021.1-to-2021.2.md

@@ -24,11 +24,13 @@ HDRP 2021.2 has various tessellation shader code to enable tessellation support
 * HDRP has improved support of motion vectors for tessellation. Only `previousPositionRWS` is part of the varyings. HDRP also added the `MotionVectorTessellation()` function. For more information, see the `MotionVectorVertexShaderCommon.hlsl` file.
 * HDRP now evaluates the `tessellationFactor` in the vertex shader and passes it to the hull shader as an interpolator. For more information, see the `VaryingMesh.hlsl` and `VertMesh.hlsl` files.
 
-### Specular Occlusion
+### Ambient Occlusion and Specular Occlusion
 
 The algorithm for computing specular occlusion from bent normals and ambient occlusion has been changed to improve visual results.
 To use the old algorithm, function calls to `GetSpecularOcclusionFromBentAO` should be replaced by calls to `GetSpecularOcclusionFromBentAO_ConeCone`
 
+The algorithm to calculate the contribution of ambient occlusion and specular occlusion to direct lighting have been change from taking into account the multi-bounce contribution (GTAOMultiBounce) to not using the multi-bounce which is more correct.
+
 ### Light list
 
 The previous `g_vLightListGlobal` uniform have been rename to explicit `g_vLightListTile` and `g_vLightListCluster` light list name. This work required to fix a wrong behavior on console.

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

@@ -44,9 +44,9 @@ void AccumulateIndirectLighting(IndirectLighting src, inout AggregateLighting ds
 struct AmbientOcclusionFactor
 {
     real3 indirectAmbientOcclusion;
-    real3 directAmbientOcclusion;
+    real directAmbientOcclusion;
     real3 indirectSpecularOcclusion;
-    real3 directSpecularOcclusion;
+    real directSpecularOcclusion;
 };
 
 // Get screen space ambient occlusion only:
@@ -105,8 +105,9 @@ void GetScreenSpaceAmbientOcclusionMultibounce(float2 positionSS, float NdotV, f
 
     aoFactor.indirectSpecularOcclusion = GTAOMultiBounce(min(specularOcclusionFromData, indirectSpecularOcclusion), fresnel0);
     aoFactor.indirectAmbientOcclusion = GTAOMultiBounce(min(ambientOcclusionFromData, indirectAmbientOcclusion), diffuseColor);
-    aoFactor.directSpecularOcclusion = GTAOMultiBounce(directSpecularOcclusion, fresnel0);
-    aoFactor.directAmbientOcclusion = GTAOMultiBounce(directAmbientOcclusion, diffuseColor);
+    // Note: when affecting direct lighting we don't used the fake bounce.
+    aoFactor.directSpecularOcclusion = directSpecularOcclusion;
+    aoFactor.directAmbientOcclusion = directAmbientOcclusion;
 }
 
 void ApplyAmbientOcclusionFactor(AmbientOcclusionFactor aoFactor, inout BuiltinData builtinData, inout AggregateLighting lighting)