From 88645c8d7a8fdc394fac6560fdd8230d6568865f Mon Sep 17 00:00:00 2001
From: Emmanuel Turquin <emmanuel@turquin.org>
Date: Thu, 16 Apr 2020 14:22:58 +0200
Subject: [PATCH] Fixed issues with path traced SSS and accumulation.

---
 .../Runtime/Material/Lit/LitPathTracing.hlsl                  | 2 +-
 .../Runtime/RenderPipeline/Accumulation/SubFrameManager.cs    | 4 +++-
 .../Runtime/RenderPipeline/PathTracing/PathTracing.cs         | 1 -
 .../Raytracing/Shaders/RayTracingSubSurface.raytrace          | 3 +--
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/com.unity.render-pipelines.high-definition/Runtime/Material/Lit/LitPathTracing.hlsl b/com.unity.render-pipelines.high-definition/Runtime/Material/Lit/LitPathTracing.hlsl
index 77d0b1cdd74..32358051f8f 100644
--- a/com.unity.render-pipelines.high-definition/Runtime/Material/Lit/LitPathTracing.hlsl
+++ b/com.unity.render-pipelines.high-definition/Runtime/Material/Lit/LitPathTracing.hlsl
@@ -103,7 +103,7 @@ bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinDa
         mtlData.subsurfaceWeightFactor = subsurfaceWeight;
 
         SSS::Result subsurfaceResult;
-        float3 meanFreePath = -0.001 / (_ShapeParamsAndMaxScatterDists[mtlData.bsdfData.diffusionProfileIndex].rgb * _WorldScalesAndFilterRadiiAndThicknessRemaps[mtlData.bsdfData.diffusionProfileIndex].x);
+        float3 meanFreePath = 0.001 / (_ShapeParamsAndMaxScatterDists[mtlData.bsdfData.diffusionProfileIndex].rgb * _WorldScalesAndFilterRadiiAndThicknessRemaps[mtlData.bsdfData.diffusionProfileIndex].x);
 
         if (!SSS::RandomWalk(shadingPosition, mtlData.bsdfData.normalWS, mtlData.bsdfData.diffuseColor, meanFreePath, pathIntersection.pixelCoord, subsurfaceResult))
             return false;
diff --git a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Accumulation/SubFrameManager.cs b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Accumulation/SubFrameManager.cs
index 745e2c52650..12f1acbb47f 100644
--- a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Accumulation/SubFrameManager.cs
+++ b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Accumulation/SubFrameManager.cs
@@ -174,7 +174,9 @@ internal Vector4 GetFrameWeights()
 
             float weight = isRecording ? ShutterProfile(time) : 1.0f;
 
-            m_AccumulatedWeight += weight;
+            if (m_CurrentIteration < m_AccumulationSamples)
+                m_AccumulatedWeight += weight;
+
             if (m_AccumulatedWeight > 0)
             {
                 return new Vector4(weight, totalWeight, 1.0f / m_AccumulatedWeight, 0.0f);
diff --git a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/PathTracing.cs b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/PathTracing.cs
index d30b4c852a7..6bc0e87bfb0 100644
--- a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/PathTracing.cs
+++ b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/PathTracing.cs
@@ -244,7 +244,6 @@ void RenderPathTracing(HDCamera hdCamera, CommandBuffer cmd, RTHandle outputText
                 cmd.SetGlobalTexture(HDShaderIDs._ScramblingTexture, m_Asset.renderPipelineResources.textures.scramblingTex);
 
                 // Inject the ray generation data
-
                 cmd.SetGlobalFloat(HDShaderIDs._RaytracingNumSamples, m_SubFrameManager.subFrameCount);
                 cmd.SetGlobalFloat(HDShaderIDs._RaytracingMinRecursion, m_PathTracingSettings.minimumDepth.value);
                 cmd.SetGlobalFloat(HDShaderIDs._RaytracingMaxRecursion, m_PathTracingSettings.maximumDepth.value);
diff --git a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/RayTracingSubSurface.raytrace b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/RayTracingSubSurface.raytrace
index ee418bafeb1..ac00a2ca669 100644
--- a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/RayTracingSubSurface.raytrace
+++ b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/RayTracingSubSurface.raytrace
@@ -76,8 +76,7 @@ void RayGenSubSurface()
     DECODE_FROM_SSSBUFFER(posInput.positionSS, sssData);
     float3 shapeParam  = _ShapeParamsAndMaxScatterDists[sssData.diffusionProfileIndex].rgb * _WorldScalesAndFilterRadiiAndThicknessRemaps[sssData.diffusionProfileIndex].x;
 
-    // Deduce our scattering distance
-    // For some reason the value in shapeParam is negative, convert it to milimeters while we are there.
+    // Deduce our scattering distance (converted to mm)
     float3 scatteringDistance = 1.0 / shapeParam * 0.001;
 
     // Define which sample in the sequence we are up to.