[HDRP][Path Tracing] Slight robustness improvement for sample rescaling

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

@@ -70,6 +70,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed unexpectedly strong contribution from directional lights in path-traced volumetric scattering (case 1304688).
 - Fixed memory leak with XR combined occlusion meshes (case 1366173).
 - Fixed diffusion profile being reset to default on SpeedTree8 materials with subsurface scattering enabled during import.
+- Fixed support for light/shadow dimmers (volumetric or not) in path tracing.
 
 ### Changed
 - Visual Environment ambient mode is now Dynamic by default.

com.unity.render-pipelines.high-definition/Runtime/Lighting/AtmosphericScattering/Fog.cs

@@ -239,6 +239,7 @@ void UpdateShaderVariablesGlobalCBFogParameters(ref ShaderVariablesGlobal cb, HD
             cb._HeightFogBaseHeight = crBaseHeight;
             cb._GlobalFogAnisotropy = anisotropy.value;
             cb._VolumetricFilteringEnabled = ((int)denoisingMode.value & (int)FogDenoisingMode.Gaussian) != 0 ? 1 : 0;
+            cb._FogDirectionalOnly = directionalLightsOnly.value ? 1 : 0;
         }
     }
 

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingLight.hlsl

@@ -12,6 +12,7 @@
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/ShaderVariablesRaytracingLightLoop.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/Shadows/SphericalQuad.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/Common/AtmosphericScatteringRayTracing.hlsl"
+#include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingSampling.hlsl"
 
 // How many lights (at most) do we support at one given shading point
 // FIXME: hardcoded limits are evil, this LightList should instead be put together in C#
@@ -327,6 +328,11 @@ float3 GetAreaEmission(LightData lightData, float centerU, float centerV, float
     return emission;
 }
 
+float3 GetLightTransmission(float3 transmission, float shadowOpacity)
+{
+    return lerp(float3(1.0, 1.0, 1.0), transmission, shadowOpacity);
+}
+
 bool SampleLights(LightList lightList,
                   float3 inputSample,
                   float3 position,
@@ -335,7 +341,8 @@ bool SampleLights(LightList lightList,
               out float3 outgoingDir,
               out float3 value,
               out float pdf,
-              out float dist)
+              out float dist,
+              out float shadowOpacity)
 {
     if (!GetLightCount(lightList))
         return false;
@@ -404,7 +411,15 @@ bool SampleLights(LightList lightList,
         }
 
         if (isVolume)
+        {
             value *= lightData.volumetricLightDimmer;
+            shadowOpacity = lightData.volumetricShadowDimmer;
+        }
+        else
+        {
+            value *= lightData.lightDimmer;
+            shadowOpacity = lightData.shadowDimmer;
+        }
 
 #ifndef LIGHT_EVALUATION_NO_HEIGHT_FOG
         ApplyFogAttenuation(position, outgoingDir, dist, value);
@@ -435,7 +450,15 @@ bool SampleLights(LightList lightList,
         dist = FLT_INF;
 
         if (isVolume)
+        {
             value *= lightData.volumetricLightDimmer;
+            shadowOpacity = lightData.volumetricShadowDimmer;
+        }
+        else
+        {
+            value *= lightData.lightDimmer;
+            shadowOpacity = lightData.shadowDimmer;
+        }
 
 #ifndef LIGHT_EVALUATION_NO_HEIGHT_FOG
         ApplyFogAttenuation(position, outgoingDir, value);
@@ -759,13 +782,13 @@ float PickLocalLightInterval(float3 rayOrigin, float3 rayDirection, inout float
                     tMin = tLightMin;
                     tMax = tLightMax;
 
-                    inputSample /= wLight;
+                    inputSample = RescaleSampleUnder(inputSample, wLight);
                 }
                 else
                 {
                     lightWeight *= 1.0 - wLight;
 
-                    inputSample = (inputSample - wLight) / (1.0 - wLight);
+                    inputSample = RescaleSampleOver(inputSample, wLight);
                 }
 
                 localCount++;
@@ -793,13 +816,13 @@ float PickLocalLightInterval(float3 rayOrigin, float3 rayDirection, inout float
                     tMin = tLightMin;
                     tMax = tLightMax;
 
-                    inputSample /= wLight;
+                    inputSample = RescaleSampleUnder(inputSample, wLight);
                 }
                 else
                 {
                     lightWeight *= 1.0 - wLight;
 
-                    inputSample = (inputSample - wLight) / (1.0 - wLight);
+                    inputSample = RescaleSampleOver(inputSample, wLight);
                 }
 
                 localCount++;

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingSampling.hlsl

@@ -44,4 +44,15 @@ bool RussianRouletteTest(float threshold, float value, float rand, out float fac
     return true;
 }
 
+float RescaleSampleUnder(float inputSample, float threshold)
+{
+    return inputSample / threshold;
+}
+
+float RescaleSampleOver(float inputSample, float threshold)
+{
+    // Make sure we never reach 1.0 due to numerical imprecision
+    return min((inputSample - threshold) / (1.0 - threshold), 0.99999);
+}
+
 #endif // UNITY_PATH_TRACING_SAMPLING_INCLUDED

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingVolume.hlsl

@@ -1,9 +1,7 @@
 #ifndef UNITY_PATH_TRACING_VOLUME_INCLUDED
 #define UNITY_PATH_TRACING_VOLUME_INCLUDED
 
-#ifdef HAS_LIGHTLOOP
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingLight.hlsl"
-#endif
 
 float ComputeHeightFogMultiplier(float height)
 {
@@ -17,42 +15,46 @@ bool SampleVolumeScatteringPosition(uint2 pixelCoord, inout float inputSample, i
     if (!_FogEnabled || !_EnableVolumetricFog)
         return false;
 
-    // This will determin the interval in which volumetric scattering can occur
+    // This will determine the interval in which volumetric scattering can occur
     float tMin, tMax;
     float pdfVol = 1.0;
     float tFog = min(t, _MaxFogDistance);
 
-#ifdef HAS_LIGHTLOOP
-
-    float pickedLightWeight;
-    float localWeight = PickLocalLightInterval(WorldRayOrigin(), WorldRayDirection(), inputSample, lightPosition, pickedLightWeight, tMin, tMax);
-
-    if (localWeight < 0.0)
-        return false;
-
-    sampleLocalLights = inputSample < localWeight;
-    if (sampleLocalLights)
+    if (_FogDirectionalOnly)
     {
-        tMax = min(tMax, tFog);
-        if (tMin >= tMax)
+        if (!_DirectionalLightCount)
             return false;
 
-        inputSample /= localWeight;
-        pdfVol *= localWeight * pickedLightWeight;
-    }
-    else
-    {
         tMin = 0.0;
         tMax = tFog;
+    }
+    else // Directional and local lights
+    {
+        float pickedLightWeight;
+        float localWeight = PickLocalLightInterval(WorldRayOrigin(), WorldRayDirection(), inputSample, lightPosition, pickedLightWeight, tMin, tMax);
+
+        if (localWeight < 0.0)
+            return false;
 
-        inputSample -= localWeight;
-        inputSample /= 1.0 - localWeight;
-        pdfVol *= 1.0 - localWeight;
+        sampleLocalLights = inputSample < localWeight;
+        if (sampleLocalLights)
+        {
+            tMax = min(tMax, tFog);
+            if (tMin >= tMax)
+                return false;
+
+            inputSample = RescaleSampleUnder(inputSample, localWeight);
+            pdfVol *= localWeight * pickedLightWeight;
+        }
+        else
+        {
+            tMin = 0.0;
+            tMax = tFog;
+
+            inputSample = RescaleSampleOver(inputSample, localWeight);
+            pdfVol *= 1.0 - localWeight;
+        }
     }
-#else
-    tMin = 0.0;
-    tMax = tFog;
-#endif
 
     // FIXME: not quite sure what the sigmaT value is supposed to be...
     const float sigmaT = _HeightFogBaseExtinction;
@@ -62,27 +64,18 @@ bool SampleVolumeScatteringPosition(uint2 pixelCoord, inout float inputSample, i
 
     if (inputSample >= transmittanceThreshold)
     {
-        // Re-scale the sample
-        inputSample -= transmittanceThreshold;
-        inputSample /= 1.0 - transmittanceThreshold;
-
-        // Adjust the pdf
+        inputSample = RescaleSampleOver(inputSample, transmittanceThreshold);
         pdf *= 1.0 - transmittanceThreshold;
 
         return false;
     }
 
-    // Re-scale the sample
-    inputSample /= transmittanceThreshold;
-
-    // Adjust the pdf
+    inputSample = RescaleSampleUnder(inputSample, transmittanceThreshold);
     pdf *= pdfVol * transmittanceThreshold;
 
     // Exponential sampling
     float transmittance = transmittanceTMax + inputSample * (transmittanceTMin - transmittanceTMax);
     t = -log(transmittance) / sigmaT;
-
-    // Adjust the pdf
     pdf *= sigmaT * transmittance / (transmittanceTMin - transmittanceTMax);
 
     return true;
@@ -94,8 +87,6 @@ void ComputeVolumeScattering(inout PathIntersection pathIntersection : SV_RayPay
     // Reset the ray intersection color, which will store our final result
     pathIntersection.value = 0.0;
 
-#ifdef HAS_LIGHTLOOP
-
     // Grab depth information
     uint currentDepth = _RaytracingMaxRecursion - pathIntersection.remainingDepth;
 
@@ -108,8 +99,7 @@ void ComputeVolumeScattering(inout PathIntersection pathIntersection : SV_RayPay
     // Create the list of active lights (a local light can be forced by providing its position)
     LightList lightList = CreateLightList(scatteringPosition, sampleLocalLights, lightPosition);
 
-    // Bunch of variables common to material and light sampling
-    float pdf;
+    float pdf, shadowOpacity;
     float3 value;
 
     RayDesc ray;
@@ -121,7 +111,7 @@ void ComputeVolumeScattering(inout PathIntersection pathIntersection : SV_RayPay
     // Light sampling
     if (computeDirect)
     {
-        if (SampleLights(lightList, inputSample, scatteringPosition, 0.0, true, ray.Direction, value, pdf, ray.TMax))
+        if (SampleLights(lightList, inputSample, scatteringPosition, 0.0, true, ray.Direction, value, pdf, ray.TMax, shadowOpacity))
         {
             // FIXME: Apply phase function and divide by pdf (only isotropic for now, and not sure about sigmaS value)
             value *= _HeightFogBaseScattering.xyz * ComputeHeightFogMultiplier(scatteringPosition.y) * INV_FOUR_PI / pdf;
@@ -137,12 +127,11 @@ void ComputeVolumeScattering(inout PathIntersection pathIntersection : SV_RayPay
                 TraceRay(_RaytracingAccelerationStructure, RAY_FLAG_ACCEPT_FIRST_HIT_AND_END_SEARCH | RAY_FLAG_FORCE_NON_OPAQUE | RAY_FLAG_SKIP_CLOSEST_HIT_SHADER,
                          RAYTRACINGRENDERERFLAG_CAST_SHADOW, 0, 1, 1, ray, nextPathIntersection);
 
-                pathIntersection.value += value * nextPathIntersection.value;
+                pathIntersection.value += value * GetLightTransmission(nextPathIntersection.value, shadowOpacity);
             }
         }
     }
 
-#endif // HAS_LIGHTLOOP
 }
 
 #endif // UNITY_PATH_TRACING_VOLUME_INCLUDED

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/ShaderPass/ShaderPassPathTracing.hlsl

@@ -4,10 +4,8 @@
 
 // Path tracing includes
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingIntersection.hlsl"
-#include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingVolume.hlsl"
 #ifdef HAS_LIGHTLOOP
-#include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingLight.hlsl"
-#include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingSampling.hlsl"
+#include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingVolume.hlsl"
 #endif
 
 float PowerHeuristic(float f, float b)
@@ -36,9 +34,9 @@ float ComputeVisibility(float3 position, float3 normal, float3 inputSample)
 
     // We will ignore value and pdf here, as we only want to catch occluders (no distance falloffs, cosines, etc.)
     float3 value;
-    float pdf;
+    float pdf, shadowOpacity;
 
-    if (SampleLights(lightList, inputSample, rayDescriptor.Origin, normal, false, rayDescriptor.Direction, value, pdf, rayDescriptor.TMax))
+    if (SampleLights(lightList, inputSample, rayDescriptor.Origin, normal, false, rayDescriptor.Direction, value, pdf, rayDescriptor.TMax, shadowOpacity))
     {
         // Shoot a transmission ray (to mark it as such, purposedly set remaining depth to an invalid value)
         PathIntersection intersection;
@@ -50,7 +48,7 @@ float ComputeVisibility(float3 position, float3 normal, float3 inputSample)
         TraceRay(_RaytracingAccelerationStructure, RAY_FLAG_ACCEPT_FIRST_HIT_AND_END_SEARCH | RAY_FLAG_FORCE_NON_OPAQUE | RAY_FLAG_SKIP_CLOSEST_HIT_SHADER,
                  RAYTRACINGRENDERERFLAG_CAST_SHADOW, 0, 1, 1, rayDescriptor, intersection);
 
-        visibility = Luminance(intersection.value);
+        visibility = Luminance(GetLightTransmission(intersection.value, shadowOpacity));
     }
 
     return visibility;
@@ -143,8 +141,7 @@ void ComputeSurfaceScattering(inout PathIntersection pathIntersection : SV_RayPa
     #endif
         LightList lightList = CreateLightList(shadingPosition, lightNormal, builtinData.renderingLayers);
 
-        // Bunch of variables common to material and light sampling
-        float pdf;
+        float pdf, shadowOpacity;
         float3 value;
         MaterialResult mtlResult;
 
@@ -157,7 +154,7 @@ void ComputeSurfaceScattering(inout PathIntersection pathIntersection : SV_RayPa
         // Light sampling
         if (computeDirect)
         {
-            if (SampleLights(lightList, inputSample.xyz, rayDescriptor.Origin, lightNormal, false, rayDescriptor.Direction, value, pdf, rayDescriptor.TMax))
+            if (SampleLights(lightList, inputSample.xyz, rayDescriptor.Origin, lightNormal, false, rayDescriptor.Direction, value, pdf, rayDescriptor.TMax, shadowOpacity))
             {
                 EvaluateMaterial(mtlData, rayDescriptor.Direction, mtlResult);
 
@@ -174,7 +171,7 @@ void ComputeSurfaceScattering(inout PathIntersection pathIntersection : SV_RayPa
                              RAYTRACINGRENDERERFLAG_CAST_SHADOW, 0, 1, 1, rayDescriptor, nextPathIntersection);
 
                     float misWeight = PowerHeuristic(pdf, mtlResult.diffPdf + mtlResult.specPdf);
-                    pathIntersection.value += value * nextPathIntersection.value * misWeight;
+                    pathIntersection.value += value * GetLightTransmission(nextPathIntersection.value, shadowOpacity) * misWeight;
                 }
             }
         }

com.unity.render-pipelines.high-definition/Runtime/ShaderLibrary/ShaderVariablesGlobal.cs

@@ -130,16 +130,16 @@ unsafe struct ShaderVariablesGlobal
         public float _FogColorMode;
         public float _GlobalMipBias;
         public float _GlobalMipBiasPow2;
-        public float _Pad2;
+        public float _Pad0;
         public Vector4 _MipFogParameters;
         public Vector4 _HeightFogBaseScattering;
         public float _HeightFogBaseExtinction;
         public float _HeightFogBaseHeight;
         public float _GlobalFogAnisotropy;
         public int _VolumetricFilteringEnabled;
         public Vector2 _HeightFogExponents; // { 1/H, H }
-        public float _Pad4;
-        public float _Pad5;
+        public int _FogDirectionalOnly;
+        public float _Pad1;
 
         // VBuffer
         public Vector4 _VBufferViewportSize;           // { w, h, 1/w, 1/h }

com.unity.render-pipelines.high-definition/Runtime/ShaderLibrary/ShaderVariablesGlobal.cs.hlsl

@@ -58,16 +58,16 @@ GLOBAL_CBUFFER_START(ShaderVariablesGlobal, b0)
     float _FogColorMode;
     float _GlobalMipBias;
     float _GlobalMipBiasPow2;
-    float _Pad2;
+    float _Pad0;
     float4 _MipFogParameters;
     float4 _HeightFogBaseScattering;
     float _HeightFogBaseExtinction;
     float _HeightFogBaseHeight;
     float _GlobalFogAnisotropy;
     int _VolumetricFilteringEnabled;
     float2 _HeightFogExponents;
-    float _Pad4;
-    float _Pad5;
+    int _FogDirectionalOnly;
+    float _Pad1;
     float4 _VBufferViewportSize;
     float4 _VBufferLightingViewportScale;
     float4 _VBufferLightingViewportLimit;