[HDRP][Path Tracing] Environment (sky) importance sampling

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

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Added FSR sharpness override to camera and pipeline asset.
 - Added an option on the lit shader to perform Planar and Triplanar mapping in Object Space.
 - Added a button in the Probe Volume Baking window to open the Probe Volume debug panel.
+- Added importance sampling of the sky in path tracing (aka environment sampling).
 
 ### Fixed
 - Fixed some XR devices: Pulling camera world space position from mainViewConstants instead of transform.

com.unity.render-pipelines.high-definition/Documentation~/Ray-Tracing-Path-Tracing.md

@@ -33,12 +33,13 @@ Path tracing uses the [Volume](Volumes.md) framework, so to enable this feature,
 
 ## Properties
 
-| Property              | Description                                                  |
-| --------------------- | ------------------------------------------------------------ |
-| **Maximum Samples**   | Set the number of frames to accumulate for the final image. There is a progress bar at the bottom of the Scene view which indicates the current accumulation with respect to this value. |
-| **Minimum Depth**     | Set the minimum number of light bounces in each path.        |
-| **Maximum Depth**     | Set the maximum number of light bounces in each path. You can not set this to be lower than Minimum Depth.<br /> **Note**: You can set this and Minimum Depth to 1 if you only want to direct lighting. You can set them both to 2 if you only want to visualize indirect lighting (which is only visible on the second bounce). |
-| **Maximum Intensity** | Set a value to clamp the intensity of the light value each bounce returns. This avoids very bright, isolated pixels in the final result.<br />**Note**: This property makes the final image dimmer, so if the result looks dark, increase the value of this property. |
+| Property                    | Description                                                  |
+| --------------------------- | ------------------------------------------------------------ |
+| **Maximum Samples**         | Set the number of frames to accumulate for the final image. There is a progress bar at the bottom of the Scene view which indicates the current accumulation with respect to this value. |
+| **Minimum Depth**           | Set the minimum number of light bounces in each path.        |
+| **Maximum Depth**           | Set the maximum number of light bounces in each path. You can not set this to be lower than Minimum Depth.<br /> **Note**: You can set this and Minimum Depth to 1 if you only want to direct lighting. You can set them both to 2 if you only want to visualize indirect lighting (which is only visible on the second bounce). |
+| **Maximum Intensity**       | Set a value to clamp the intensity of the light value each bounce returns. This avoids very bright, isolated pixels in the final result.<br />**Note**: This property can make the final image dimmer, so if the result looks dark, increase the value of this property. |
+| **Sky Importance Sampling** | Set the sky sampling mode. Importance sampling favors the brightest directions, which is beneficial when using a sky model with high contrast and very intense spots (like a sun, or street lights). On the other hand, it can be slightly detrimental when using a smooth, uniform sky. It is active by default for HDRI skies only, but can also be turned On and Off, regardless of the type of sky in use. |
 
 ![](Images/RayTracingPathTracing4.png)
 

com.unity.render-pipelines.high-definition/Editor/RenderPipeline/PathTracing/PathTracingEditor.cs

@@ -17,6 +17,7 @@ class PathTracingEditor : VolumeComponentEditor
         SerializedDataParameter m_MinDepth;
         SerializedDataParameter m_MaxDepth;
         SerializedDataParameter m_MaxIntensity;
+        SerializedDataParameter m_SkyImportanceSampling;
 
         public override void OnEnable()
         {
@@ -28,6 +29,7 @@ public override void OnEnable()
             m_MinDepth = Unpack(o.Find(x => x.minimumDepth));
             m_MaxDepth = Unpack(o.Find(x => x.maximumDepth));
             m_MaxIntensity = Unpack(o.Find(x => x.maximumIntensity));
+            m_SkyImportanceSampling = Unpack(o.Find(x => x.skyImportanceSampling));
         }
 
         public override void OnInspectorGUI()
@@ -54,6 +56,7 @@ public override void OnInspectorGUI()
                         PropertyField(m_MinDepth);
                         PropertyField(m_MaxDepth);
                         PropertyField(m_MaxIntensity);
+                        PropertyField(m_SkyImportanceSampling);
                     }
 
                     // Make sure MaxDepth is always greater or equal than MinDepth

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.cs

@@ -461,7 +461,7 @@ public HDRenderPipeline(HDRenderPipelineAsset asset)
                 InitRayTracedIndirectDiffuse();
                 InitRaytracingDeferred();
                 InitRecursiveRenderer();
-                InitPathTracing(m_RenderGraph);
+                InitPathTracing();
                 InitRayTracingAmbientOcclusion();
             }
 

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipelineRayTracingResources.cs

@@ -69,7 +69,9 @@ partial class HDRenderPipelineRayTracingResources : HDRenderPipelineResources
 
         // Path Tracing
         [Reload("Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMain.raytrace")]
-        public RayTracingShader pathTracing;
+        public RayTracingShader pathTracingRT;
+        [Reload("Runtime/RenderPipeline/PathTracing/Shaders/PathTracingSkySamplingData.compute")]
+        public ComputeShader pathTracingSkySamplingDataCS;
 
         // Ray Marching
         [Reload("Runtime/RenderPipeline/Raytracing/Shaders/RayMarching.compute")]

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDStringConstants.cs

@@ -628,6 +628,12 @@ static class HDShaderIDs
         public static readonly int _InvViewportScaleBias = Shader.PropertyToID("_InvViewportScaleBias");
         public static readonly int _PathTracingDoFParameters = Shader.PropertyToID("_PathTracingDoFParameters");
         public static readonly int _PathTracingTilingParameters = Shader.PropertyToID("_PathTracingTilingParameters");
+        public static readonly int _PathTracingCameraSkyEnabled = Shader.PropertyToID("_PathTracingCameraSkyEnabled");
+        public static readonly int _PathTracingCameraClearColor = Shader.PropertyToID("_PathTracingCameraClearColor");
+        public static readonly int _PathTracingSkyTextureWidth = Shader.PropertyToID("_PathTracingSkyTextureWidth");
+        public static readonly int _PathTracingSkyTextureHeight = Shader.PropertyToID("_PathTracingSkyTextureHeight");
+        public static readonly int _PathTracingSkyCDFTexture = Shader.PropertyToID("_PathTracingSkyCDFTexture");
+        public static readonly int _PathTracingSkyMarginalTexture = Shader.PropertyToID("_PathTracingSkyMarginalTexture");
 
         // Light Cluster
         public static readonly int _LightDatasRT = Shader.PropertyToID("_LightDatasRT");
@@ -740,8 +746,6 @@ static class HDShaderIDs
         // Primary Visibility
         public static readonly int _RaytracingFlagMask = Shader.PropertyToID("_RaytracingFlagMask");
         public static readonly int _RaytracingPrimaryDebug = Shader.PropertyToID("_RaytracingPrimaryDebug");
-        public static readonly int _RaytracingCameraSkyEnabled = Shader.PropertyToID("_RaytracingCameraSkyEnabled");
-        public static readonly int _RaytracingCameraClearColor = Shader.PropertyToID("_RaytracingCameraClearColor");
 
         // Indirect diffuse
         public static readonly int _IndirectDiffuseTexture = Shader.PropertyToID("_IndirectDiffuseTexture");