Update algorithm for specular occlusion

com.unity.render-pipelines.core/ShaderLibrary/CommonLighting.hlsl

@@ -245,7 +245,7 @@ real3 GTAOMultiBounce(real visibility, real3 albedo)
     return max(x, ((x * a + b) * x + c) * x);
 }
 
-// Based on Oat and Sander's 2008 technique
+// Based on Oat and Sander's 2007 technique
 // Area/solidAngle of intersection of two cone
 real SphericalCapIntersectionSolidArea(real cosC1, real cosC2, real cosB)
 {
@@ -279,7 +279,7 @@ real SphericalCapIntersectionSolidArea(real cosC1, real cosC2, real cosB)
 // ref: Practical Realtime Strategies for Accurate Indirect Occlusion
 // http://blog.selfshadow.com/publications/s2016-shading-course/#course_content
 // Original Cone-Cone method with cosine weighted assumption (p129 s2016_pbs_activision_occlusion)
-real GetSpecularOcclusionFromBentAO(real3 V, real3 bentNormalWS, real3 normalWS, real ambientOcclusion, real roughness)
+real GetSpecularOcclusionFromBentAO_ConeCone(real3 V, real3 bentNormalWS, real3 normalWS, real ambientOcclusion, real roughness)
 {
     // Retrieve cone angle
     // Ambient occlusion is cosine weighted, thus use following equation. See slide 129
@@ -290,6 +290,40 @@ real GetSpecularOcclusionFromBentAO(real3 V, real3 bentNormalWS, real3 normalWS,
     return SphericalCapIntersectionSolidArea(cosAv, cosAs, cosB) / (TWO_PI * (1.0 - cosAs));
 }
 
+real GetSpecularOcclusionFromBentAO(real3 V, real3 bentNormalWS, real3 normalWS, real ambientOcclusion, real roughness)
+{
+    // Pseudo code:
+    //SphericalGaussian NDF = WarpedGGXDistribution(normalWS, roughness, V);
+    //SphericalGaussian Visibility = VisibilityConeSG(bentNormalWS, ambientOcclusion);
+    //SphericalGaussian UpperHemisphere = UpperHemisphereSG(normalWS);
+    //return saturate( InnerProduct(NDF, Visibility) / InnerProduct(NDF, UpperHemisphere) );
+
+    // 1. Approximate visibility cone with a spherical gaussian of amplitude A=1
+    // For a cone angle X, we can determine sharpness so that all point inside the cone have a value > Y
+    // sharpness = (log(Y) - log(A)) / (cos(X) - 1)
+    // For AO cone, cos(X) = sqrt(1 - ambientOcclusion)
+    // -> for Y = 0.1, sharpness = -1.0 / (sqrt(1-ao) - 1)
+    float vs = -1.0f / (sqrt(1.0f - ambientOcclusion) - 1.0f);
+
+    // 2. Approximate upper hemisphere with sharpness = 0.8 and amplitude = 1
+    float us = 0.8f;
+
+    // 3. Compute warped SG Axis of GGX distribution
+    // Ref: All-Frequency Rendering of Dynamic, Spatially-Varying Reflectance
+    // https://www.microsoft.com/en-us/research/wp-content/uploads/2009/12/sg.pdf
+    float NoV = dot(V, normalWS);
+    float3 NDFAxis = (2 * NoV * normalWS - V) * (0.5f / max(roughness * roughness * NoV, 0.001f));
+
+    float umLength1 = length(NDFAxis + vs * bentNormalWS);
+    float umLength2 = length(NDFAxis + us * normalWS);
+    float d1 = 1 - exp(-2 * umLength1);
+    float d2 = 1 - exp(-2 * umLength2);
+
+    float expFactor1 = exp(umLength1 - umLength2 + us - vs);
+
+    return saturate(expFactor1 * (d1 * umLength2) / (d2 * umLength1));
+}
+
 // Ref: Steve McAuley - Energy-Conserving Wrapped Diffuse
 real ComputeWrappedDiffuseLighting(real NdotL, real w)
 {

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

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Significantly improved performance of APV probe debug.
 - Removed DLSS keyword in settings search when NVIDIA package is not installed. (case 1358409)
 - Fixed light anchor min distance value + properties not working with prefabs (case 1345509).
+- Fixed specular occlusion sharpness and over darkening at grazing angles.
 
 ### changed
 - Visual Environment ambient mode is now Dynamic by default.
@@ -390,7 +391,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed wrong ordering in FrameSettings (Normalize Reflection Probes)
 - Fixed ThreadMapDetail to saturate AO & smoothness strength inputs to prevent out-of-bounds values set by users (1357740)
 - Allow negative wind speed parameter.
-- Viewport and scaling of Custom post process when TAAU or DLSS are enabled (case 1352407).
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard

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

@@ -39,6 +39,11 @@ 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
+
+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`
+
 ## Density Volumes
 
 Density Volumes are now known as **Local Volumetric Fog**.

com.unity.render-pipelines.high-definition/Editor/Material/ShaderGraph/TargetData/LightingData.cs

@@ -74,7 +74,7 @@ public bool specularAA
         // }
 
         [SerializeField]
-        SpecularOcclusionMode m_SpecularOcclusionMode;
+        SpecularOcclusionMode m_SpecularOcclusionMode = SpecularOcclusionMode.FromAO;
         public SpecularOcclusionMode specularOcclusionMode
         {
             get => m_SpecularOcclusionMode;

com.unity.render-pipelines.high-definition/Runtime/Material/LayeredLit/LayeredLit.shader

@@ -244,7 +244,7 @@ Shader "HDRP/LayeredLit"
 
         // Following are builtin properties
 
-        [Enum(Off, 0, From Ambient Occlusion, 1, From Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
+        [Enum(Off, 0, From Ambient Occlusion, 1, From AO and Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
 
         [HDR] _EmissiveColor("EmissiveColor", Color) = (0, 0, 0)
         // Used only to serialize the LDR and HDR emissive color in the material UI,
@@ -453,7 +453,7 @@ Shader "HDRP/LayeredLit"
     #pragma shader_feature_fragment _ENABLESPECULAROCCLUSION                     // Non-local
     #pragma shader_feature_fragment _ _SPECULAR_OCCLUSION_NONE _SPECULAR_OCCLUSION_FROM_BENT_NORMAL_MAP // Non-local
     #pragma shader_feature_raytracing _ENABLESPECULAROCCLUSION                     // Non-local
-    #pragma shader_feature_raytracing _ SPECULAR_OCCLUSION_NONE _SPECULAR_OCCLUSION_FROM_BENT_NORMAL_MAP // Non-local
+    #pragma shader_feature_raytracing _ _SPECULAR_OCCLUSION_NONE _SPECULAR_OCCLUSION_FROM_BENT_NORMAL_MAP // Non-local
 
     #ifdef _ENABLESPECULAROCCLUSION
     #define _SPECULAR_OCCLUSION_FROM_BENT_NORMAL_MAP

com.unity.render-pipelines.high-definition/Runtime/Material/LayeredLit/LayeredLitTessellation.shader

@@ -244,7 +244,7 @@ Shader "HDRP/LayeredLitTessellation"
 
         // Following are builtin properties
 
-        [Enum(Off, 0, From Ambient Occlusion, 1, From Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
+        [Enum(Off, 0, From Ambient Occlusion, 1, From AO and Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
 
         [HDR] _EmissiveColor("EmissiveColor", Color) = (0, 0, 0)
         // Used only to serialize the LDR and HDR emissive color in the material UI,

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

@@ -77,7 +77,7 @@ Shader "HDRP/Lit"
 
         // Following options are for the GUI inspector and different from the input parameters above
         // These option below will cause different compilation flag.
-        [Enum(Off, 0, From Ambient Occlusion, 1, From Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
+        [Enum(Off, 0, From Ambient Occlusion, 1, From AO and Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
 
         [HDR] _EmissiveColor("EmissiveColor", Color) = (0, 0, 0)
         // Used only to serialize the LDR and HDR emissive color in the material UI,

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

@@ -17,9 +17,6 @@
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/Material/Lit/LitDecalData.hlsl"
 #endif
 
-//#include "Packages/com.unity.render-pipelines.high-definition/Runtime/Material/SphericalCapPivot/SPTDistribution.hlsl"
-//#define SPECULAR_OCCLUSION_USE_SPTD
-
 //#define PROJECTED_SPACE_NDF_FILTERING
 
 // Struct that gather UVMapping info of all layers + common calculation
@@ -286,11 +283,7 @@ void GetSurfaceAndBuiltinData(FragInputs input, float3 V, inout PositionInputs p
     // If user provide bent normal then we process a better term
 #if defined(_BENTNORMALMAP) && defined(_SPECULAR_OCCLUSION_FROM_BENT_NORMAL_MAP)
     // If we have bent normal and ambient occlusion, process a specular occlusion
-    #ifdef SPECULAR_OCCLUSION_USE_SPTD
-    surfaceData.specularOcclusion = GetSpecularOcclusionFromBentAOPivot(V, bentNormalWS, surfaceData.normalWS, surfaceData.ambientOcclusion, PerceptualSmoothnessToPerceptualRoughness(surfaceData.perceptualSmoothness));
-    #else
     surfaceData.specularOcclusion = GetSpecularOcclusionFromBentAO(V, bentNormalWS, surfaceData.normalWS, surfaceData.ambientOcclusion, PerceptualSmoothnessToRoughness(surfaceData.perceptualSmoothness));
-#endif
     // Don't do spec occ from Ambient if there is no mask mask
 #elif defined(_MASKMAP) && !defined(_SPECULAR_OCCLUSION_NONE)
     surfaceData.specularOcclusion = GetSpecularOcclusionFromAmbientOcclusion(ClampNdotV(dot(surfaceData.normalWS, V)), surfaceData.ambientOcclusion, PerceptualSmoothnessToRoughness(surfaceData.perceptualSmoothness));

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

@@ -22,6 +22,8 @@ TEXTURE2D(_MaskMap);
 SAMPLER(sampler_MaskMap);
 TEXTURE2D(_BentNormalMap); // Reuse sampler from normal map
 SAMPLER(sampler_BentNormalMap);
+TEXTURE2D(_BentNormalMapOS);
+SAMPLER(sampler_BentNormalMapOS);
 
 TEXTURE2D(_NormalMap);
 SAMPLER(sampler_NormalMap);

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

@@ -77,7 +77,7 @@ Shader "HDRP/LitTessellation"
 
         // Following options are for the GUI inspector and different from the input parameters above
         // These option below will cause different compilation flag.
-        [Enum(Off, 0, From Ambient Occlusion, 1, From Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
+        [Enum(Off, 0, From Ambient Occlusion, 1, From AO and Bent Normals, 2)]  _SpecularOcclusionMode("Specular Occlusion Mode", Int) = 1
 
         [HDR] _EmissiveColor("EmissiveColor", Color) = (0, 0, 0)
         // Used only to serialize the LDR and HDR emissive color in the material UI,