[HDRP][Path Tracing] Replaced recursive continuation rays with loop in ray generation

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

@@ -42,6 +42,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Make Vertical gate fit the default for physical camera.
 - Changed how the ambient probe is sent to the volumetric clouds trace pass (case 1381761).
 - Moved custom Sensor Lidar path tracing code to the SensorSDK package.
+- Path Tracing has moved from a recursive to an iterative implementation.
 
 ### Fixed
 - Fixed build warnings due to the exception in burst code (case 1382827).

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

@@ -1,4 +1,4 @@
-#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/PathTracingPayload.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMaterial.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingBSDF.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingAOV.hlsl"
@@ -21,13 +21,13 @@ float GetSpecularCoeffSum(MaterialData mtlData)
 }
 #endif
 
-void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData, MaterialData mtlData, inout BSDFData bsdfData)
+void ProcessBSDFData(PathPayload payload, BuiltinData builtinData, MaterialData mtlData, inout BSDFData bsdfData)
 {
     // Adjust roughness to reduce fireflies
-    bsdfData.roughness.x = max(pathIntersection.maxRoughness, bsdfData.roughness.x);
-    bsdfData.roughness.y = max(pathIntersection.maxRoughness, bsdfData.roughness.y);
+    bsdfData.roughness.x = max(payload.maxRoughness, bsdfData.roughness.x);
+    bsdfData.roughness.y = max(payload.maxRoughness, bsdfData.roughness.y);
 #ifdef _AXF_BRDF_TYPE_CAR_PAINT
-    bsdfData.roughness.z = max(pathIntersection.maxRoughness, bsdfData.roughness.z);
+    bsdfData.roughness.z = max(payload.maxRoughness, bsdfData.roughness.z);
 #endif
 
     // One of the killer features of AxF, optional specular Fresnel...
@@ -47,13 +47,13 @@ void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData,
 #endif
 }
 
-bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
+bool CreateMaterialData(PathPayload payload, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
 {
     // Alter values in the material's bsdfData struct, to better suit path tracing
     mtlData.V = -WorldRayDirection();
     mtlData.Nv = ComputeConsistentShadingNormal(mtlData.V, bsdfData.geomNormalWS, bsdfData.normalWS);
     mtlData.bsdfData = bsdfData;
-    ProcessBSDFData(pathIntersection, builtinData, mtlData, mtlData.bsdfData);
+    ProcessBSDFData(payload, builtinData, mtlData, mtlData.bsdfData);
 
     mtlData.bsdfWeight = 0.0;
 
@@ -109,13 +109,14 @@ float AdjustPathRoughness(MaterialData mtlData, MaterialResult mtlResult, bool i
     return adjustedPathRoughness;
 }
 
-float3 ApplyAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow, float3 value)
+float3 GetMaterialAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow)
 {
-    return value;
+    // No absorption here
+    return 1.0;
 }
 
-void GetAOVData(MaterialData mtlData, out AOVData aovData)
+void GetAOVData(BSDFData bsdfData, out AOVData aovData)
 {
-    aovData.albedo = mtlData.bsdfData.diffuseColor;
-    aovData.normal = mtlData.bsdfData.normalWS;
+    aovData.albedo = bsdfData.diffuseColor;
+    aovData.normal = bsdfData.normalWS;
 }

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

@@ -1,4 +1,4 @@
-#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/PathTracingPayload.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMaterial.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingBSDF.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingAOV.hlsl"
@@ -15,11 +15,11 @@
 // bsdfWeight1  Spec GGX BRDF
 // bsdfWeight2  Diffuse BTDF
 
-void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData, inout BSDFData bsdfData)
+void ProcessBSDFData(PathPayload payload, BuiltinData builtinData, inout BSDFData bsdfData)
 {
     // Adjust roughness to reduce fireflies
-    bsdfData.roughnessT = max(pathIntersection.maxRoughness, bsdfData.roughnessT);
-    bsdfData.roughnessB = max(pathIntersection.maxRoughness, bsdfData.roughnessB);
+    bsdfData.roughnessT = max(payload.maxRoughness, bsdfData.roughnessT);
+    bsdfData.roughnessB = max(payload.maxRoughness, bsdfData.roughnessB);
 
     if (HasFlag(bsdfData.materialFeatures, MATERIALFEATUREFLAGS_FABRIC_COTTON_WOOL))
     {
@@ -28,11 +28,11 @@ void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData,
     }
 }
 
-bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
+bool CreateMaterialData(PathPayload payload, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
 {
     // Alter values in the material's bsdfData struct, to better suit path tracing
     mtlData.bsdfData = bsdfData;
-    ProcessBSDFData(pathIntersection, builtinData, mtlData.bsdfData);
+    ProcessBSDFData(payload, builtinData, mtlData.bsdfData);
 
     mtlData.bsdfWeight = 0.0;
     mtlData.V = -WorldRayDirection();
@@ -67,7 +67,7 @@ bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinDa
 
     if (HasFlag(mtlData.bsdfData.materialFeatures, MATERIALFEATUREFLAGS_FABRIC_SUBSURFACE_SCATTERING))
     {
-        float subsurfaceWeight = mtlData.bsdfWeight[0] * mtlData.bsdfData.subsurfaceMask * (1.0 - pathIntersection.maxRoughness);
+        float subsurfaceWeight = mtlData.bsdfWeight[0] * mtlData.bsdfData.subsurfaceMask * (1.0 - payload.maxRoughness);
 
         mtlData.isSubsurface = theSample < subsurfaceWeight;
         if (mtlData.isSubsurface)
@@ -79,7 +79,7 @@ bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinDa
             SSS::Result subsurfaceResult;
             float3 meanFreePath = 0.001 / (_ShapeParamsAndMaxScatterDists[mtlData.bsdfData.diffusionProfileIndex].rgb * _WorldScalesAndFilterRadiiAndThicknessRemaps[mtlData.bsdfData.diffusionProfileIndex].x);
 
-            if (!SSS::RandomWalk(shadingPosition, GetDiffuseNormal(mtlData), mtlData.bsdfData.diffuseColor, meanFreePath, pathIntersection.pixelCoord, subsurfaceResult, hasTransmission))
+            if (!SSS::RandomWalk(shadingPosition, GetDiffuseNormal(mtlData), mtlData.bsdfData.diffuseColor, meanFreePath, payload.pixelCoord, subsurfaceResult, hasTransmission))
                 return false;
 
             shadingPosition = subsurfaceResult.exitPosition;
@@ -280,14 +280,14 @@ float AdjustPathRoughness(MaterialData mtlData, MaterialResult mtlResult, bool i
     return (mtlResult.specPdf * max(mtlData.bsdfData.roughnessT, mtlData.bsdfData.roughnessB) + mtlResult.diffPdf) / (mtlResult.diffPdf + mtlResult.specPdf);
 }
 
-float3 ApplyAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow, float3 value)
+float3 GetMaterialAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow)
 {
     // No absorption here
-    return value;
+    return 1.0;
 }
 
-void GetAOVData(MaterialData mtlData, out AOVData aovData)
+void GetAOVData(BSDFData bsdfData, out AOVData aovData)
 {
-    aovData.albedo = mtlData.bsdfData.diffuseColor;
-    aovData.normal = mtlData.bsdfData.normalWS;
+    aovData.albedo = bsdfData.diffuseColor;
+    aovData.normal = bsdfData.normalWS;
 }

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

@@ -1,4 +1,4 @@
-#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/PathTracingPayload.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMaterial.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingBSDF.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingAOV.hlsl"
@@ -19,26 +19,26 @@ float2 DemuxFloat(float x)
 
 // --------------------------------------------------------------------------------------
 
-void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData, inout BSDFData bsdfData)
+void ProcessBSDFData(PathPayload payload, BuiltinData builtinData, inout BSDFData bsdfData)
 {
     // NOTE: Currently we don't support ray-aligned ribbons in the acceleration structure, so our only H-calculation routines
     // are either stochastic or derived from a tube intersection.
 #if 0
     bsdfData.h = GetHFromTube(-WorldRayDirection(), bsdfData.normalWS, bsdfData.hairStrandDirectionWS);
 #else
-    bsdfData.h = -1 + 2 * InterleavedGradientNoise(pathIntersection.pixelCoord, _RaytracingSampleIndex);
+    bsdfData.h = -1 + 2 * InterleavedGradientNoise(payload.pixelCoord, _RaytracingSampleIndex);
 #endif
 }
 
-bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
+bool CreateMaterialData(PathPayload payload, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
 {
     // Kajiya not supported.
     if (HasFlag(bsdfData.materialFeatures, MATERIALFEATUREFLAGS_HAIR_KAJIYA_KAY))
         return false;
 
     // Alter values in the material's bsdfData struct, to better suit path tracing
     mtlData.bsdfData = bsdfData;
-    ProcessBSDFData(pathIntersection, builtinData, mtlData.bsdfData);
+    ProcessBSDFData(payload, builtinData, mtlData.bsdfData);
 
     mtlData.bsdfWeight = 0.0;
     mtlData.V = -WorldRayDirection();
@@ -104,19 +104,17 @@ float3 GetLightNormal(MaterialData mtlData)
 float AdjustPathRoughness(MaterialData mtlData, MaterialResult mtlResult, bool isSampleBelow, float pathRoughness)
 {
     // TODO
-
     return pathRoughness;
 }
 
-float3 ApplyAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow, float3 value)
+float3 GetMaterialAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow)
 {
     // TODO
-
-    return value;
+    return 1.0;
 }
 
-void GetAOVData(MaterialData mtlData, out AOVData aovData)
+void GetAOVData(BSDFData bsdfData, out AOVData aovData)
 {
-    aovData.albedo = mtlData.bsdfData.diffuseColor;
-    aovData.normal = mtlData.bsdfData.normalWS;
+    aovData.albedo = bsdfData.diffuseColor;
+    aovData.normal = bsdfData.normalWS;
 }

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

@@ -1,4 +1,4 @@
-#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/PathTracingPayload.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMaterial.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingBSDF.hlsl"
 #include "Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingAOV.hlsl"
@@ -15,11 +15,11 @@ float3 GetSpecularCompensation(MaterialData mtlData)
     return 1.0 + mtlData.bsdfData.specularOcclusion * mtlData.bsdfData.fresnel0;
 }
 
-void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData, MaterialData mtlData, inout BSDFData bsdfData)
+void ProcessBSDFData(PathPayload payload, BuiltinData builtinData, MaterialData mtlData, inout BSDFData bsdfData)
 {
     // Adjust roughness to reduce fireflies
-    bsdfData.roughnessT = max(pathIntersection.maxRoughness, bsdfData.roughnessT);
-    bsdfData.roughnessB = max(pathIntersection.maxRoughness, bsdfData.roughnessB);
+    bsdfData.roughnessT = max(payload.maxRoughness, bsdfData.roughnessT);
+    bsdfData.roughnessB = max(payload.maxRoughness, bsdfData.roughnessB);
 
     float NdotV = abs(dot(GetSpecularNormal(mtlData), mtlData.V));
 
@@ -46,13 +46,13 @@ void ProcessBSDFData(PathIntersection pathIntersection, BuiltinData builtinData,
 #endif
 }
 
-bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
+bool CreateMaterialData(PathPayload payload, BuiltinData builtinData, BSDFData bsdfData, inout float3 shadingPosition, inout float theSample, out MaterialData mtlData)
 {
     // Alter values in the material's bsdfData struct, to better suit path tracing
     mtlData.V = -WorldRayDirection();
     mtlData.Nv = ComputeConsistentShadingNormal(mtlData.V, bsdfData.geomNormalWS, bsdfData.normalWS);
     mtlData.bsdfData = bsdfData;
-    ProcessBSDFData(pathIntersection, builtinData, mtlData, mtlData.bsdfData);
+    ProcessBSDFData(payload, builtinData, mtlData, mtlData.bsdfData);
 
     mtlData.bsdfWeight = 0.0;
 
@@ -92,7 +92,7 @@ bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinDa
     mtlData.bsdfWeight /= wSum;
 
 #ifdef _MATERIAL_FEATURE_SUBSURFACE_SCATTERING
-    float subsurfaceWeight = mtlData.bsdfWeight[0] * mtlData.bsdfData.subsurfaceMask * (1.0 - pathIntersection.maxRoughness);
+    float subsurfaceWeight = mtlData.bsdfWeight[0] * mtlData.bsdfData.subsurfaceMask * (1.0 - payload.maxRoughness);
 
     mtlData.isSubsurface = theSample < subsurfaceWeight;
     if (mtlData.isSubsurface)
@@ -109,7 +109,7 @@ bool CreateMaterialData(PathIntersection pathIntersection, BuiltinData builtinDa
 #else
         bool isThin = false;
 #endif
-        if (!SSS::RandomWalk(shadingPosition, GetDiffuseNormal(mtlData), mtlData.bsdfData.diffuseColor, meanFreePath, pathIntersection.pixelCoord, subsurfaceResult, isThin))
+        if (!SSS::RandomWalk(shadingPosition, GetDiffuseNormal(mtlData), mtlData.bsdfData.diffuseColor, meanFreePath, payload.pixelCoord, subsurfaceResult, isThin))
             return false;
 
         shadingPosition = subsurfaceResult.exitPosition;
@@ -353,26 +353,26 @@ float AdjustPathRoughness(MaterialData mtlData, MaterialResult mtlResult, bool i
     return adjustedPathRoughness;
 }
 
-float3 ApplyAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow, float3 value)
+float3 GetMaterialAbsorption(MaterialData mtlData, SurfaceData surfaceData, float dist, bool isSampleBelow)
 {
 #if defined(_SURFACE_TYPE_TRANSPARENT) && HAS_REFRACTION
     // Apply absorption on rays below the interface, using Beer-Lambert's law
     if (isSampleBelow)
     {
     #ifdef _REFRACTION_THIN
-        value *= exp(-mtlData.bsdfData.absorptionCoefficient * REFRACTION_THIN_DISTANCE);
+        return exp(-mtlData.bsdfData.absorptionCoefficient * REFRACTION_THIN_DISTANCE);
     #else
         // We allow a reasonable max distance of 10 times the "atDistance" (so that objects do not end up appearing black)
-        value *= exp(-mtlData.bsdfData.absorptionCoefficient * min(dist, surfaceData.atDistance * 10.0));
+        return exp(-mtlData.bsdfData.absorptionCoefficient * min(dist, surfaceData.atDistance * 10.0));
     #endif
     }
 #endif
 
-    return value;
+    return 1.0;
 }
 
-void GetAOVData(MaterialData mtlData, out AOVData aovData)
+void GetAOVData(BSDFData bsdfData, out AOVData aovData)
 {
-    aovData.albedo = mtlData.bsdfData.diffuseColor;
-    aovData.normal = mtlData.bsdfData.normalWS;
+    aovData.albedo = bsdfData.diffuseColor;
+    aovData.normal = bsdfData.normalWS;
 }