[HDRP][Path Tracing] Added proper support for interleaved tiling (#5953)

* Added ortho cam support, plus raygen refactor.

* Added support for interleaved tiling.

* Added spread angle adjustment.

* Offset tile sub-pixels, instead of relying on proj matrix modifications.

* Undoed last commit.

* Use tiled pixel coords for all things sampling-related (incl. lens).

* Update CHANGELOG.md

Co-authored-by: sebastienlagarde <sebastien@unity3d.com>

Author: eturquin

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

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix API warnings in Matcap mode on Metal.
 - Fix D3D validation layer errors w.r.t shadow textures when an atlas is not used.
 - Fixed compatibility message not displayed correctly when switching platforms.
+- Fixed support for interleaved tiling in path tracing.
 
 ### Changed
 - Changed the max distance for Light Anchors to avoid unstability with high values (case 1362802).

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

@@ -589,8 +589,9 @@ static class HDShaderIDs
         public static readonly string _RaytracingAccelerationStructureName = "_RaytracingAccelerationStructure";
 
         // Path tracing variables
-        public static readonly int _PathTracedDoFConstants = Shader.PropertyToID("_PathTracedDoFConstants");
         public static readonly int _InvViewportScaleBias = Shader.PropertyToID("_InvViewportScaleBias");
+        public static readonly int _PathTracingDoFParameters = Shader.PropertyToID("_PathTracingDoFParameters");
+        public static readonly int _PathTracingTilingParameters = Shader.PropertyToID("_PathTracingTilingParameters");
 
         // Light Cluster
         public static readonly int _LightDatasRT = Shader.PropertyToID("_LightDatasRT");

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

@@ -51,6 +51,12 @@ public sealed class PathTracing : VolumeComponent
         [Tooltip("Defines the maximum, post-exposed luminance computed for indirect path segments. Lower values help against noise and fireflies (very bright pixels), but introduce bias by darkening the overall result. Increase this value if your image looks too dark.")]
         public MinFloatParameter maximumIntensity = new MinFloatParameter(10f, 0f);
 
+        /// <summary>
+        /// Defines the number of tiles (X: width, Y: height) and the indices of the current tile (Z: i in [0, width[, W: j in [0, height[) for interleaved tiled rendering.
+        /// </summary>
+        [Tooltip("Defines the number of tiles (X: width, Y: height) and the indices of the current tile (Z: i in [0, width[, W: j in [0, height[) for interleaved tiled rendering.")]
+        public Vector4Parameter tilingParameters = new Vector4Parameter(new Vector4(1, 1, 0, 0));
+
         /// <summary>
         /// Default constructor for the path tracing volume component.
         /// </summary>
@@ -253,6 +259,7 @@ class RenderPathTracingData
             public Texture skyReflection;
             public Matrix4x4 pixelCoordToViewDirWS;
             public Vector4 dofParameters;
+            public Vector4 tilingParameters;
             public int width, height;
             public RayTracingAccelerationStructure accelerationStructure;
             public HDRaytracingLightCluster lightCluster;
@@ -272,6 +279,7 @@ TextureHandle RenderPathTracing(RenderGraph renderGraph, HDCamera hdCamera, in C
                 passData.skyReflection = m_SkyManager.GetSkyReflection(hdCamera);
                 passData.pixelCoordToViewDirWS = hdCamera.mainViewConstants.pixelCoordToViewDirWS;
                 passData.dofParameters = ComputeDoFConstants(hdCamera, m_PathTracingSettings);
+                passData.tilingParameters = m_PathTracingSettings.tilingParameters.value;
                 passData.width = hdCamera.actualWidth;
                 passData.height = hdCamera.actualHeight;
                 passData.accelerationStructure = RequestAccelerationStructure();
@@ -319,7 +327,8 @@ TextureHandle RenderPathTracing(RenderGraph renderGraph, HDCamera hdCamera, in C
                         // Additional data for path tracing
                         ctx.cmd.SetRayTracingTextureParam(data.pathTracingShader, HDShaderIDs._FrameTexture, data.output);
                         ctx.cmd.SetRayTracingMatrixParam(data.pathTracingShader, HDShaderIDs._PixelCoordToViewDirWS, data.pixelCoordToViewDirWS);
-                        ctx.cmd.SetRayTracingVectorParam(data.pathTracingShader, HDShaderIDs._PathTracedDoFConstants, data.dofParameters);
+                        ctx.cmd.SetRayTracingVectorParam(data.pathTracingShader, HDShaderIDs._PathTracingDoFParameters, data.dofParameters);
+                        ctx.cmd.SetRayTracingVectorParam(data.pathTracingShader, HDShaderIDs._PathTracingTilingParameters, data.tilingParameters);
 
                         // Run the computation
                         ctx.cmd.DispatchRays(data.pathTracingShader, "RayGen", (uint)data.width, (uint)data.height, 1);

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingMain.raytrace

@@ -27,13 +27,12 @@ float4x4 _PixelCoordToViewDirWS;
 int      _RaytracingCameraSkyEnabled;
 float4   _RaytracingCameraClearColor;
 TEXTURE2D_X(_SkyCameraTexture);
+float4   _PathTracingDoFParameters;    // x: aperture radius, y: focus distance, zw: unused
+float4   _PathTracingTilingParameters; // xy: tile count, zw: current tile index
 
 // Output(s)
 RW_TEXTURE2D_X(float4, _FrameTexture);
 
-// DoF related parameters
-float4 _PathTracedDoFConstants; // x: aperture radius, y: focus distance, zw: unused
-
 [shader("miss")]
 void MissCamera(inout PathIntersection pathIntersection : SV_RayPayload)
 {
@@ -92,19 +91,17 @@ void MissMaterial(inout PathIntersection pathIntersection : SV_RayPayload)
 
 void ApplyDepthOfField(uint2 pixelCoord, float dotDirection, inout float3 origin, inout float3 direction)
 {
-    float apertureRadius = _PathTracedDoFConstants.x;
-
-    if (apertureRadius <= 0.0)
+     // Check aperture radius
+    if (_PathTracingDoFParameters.x <= 0.0)
         return;
 
     // Sample the lens aperture using the next available dimensions
     // (we use 40 for path tracing, 2 for sub-pixel jittering, 64 for SSS -> 106, 107)
-    float2 uv = apertureRadius * SampleDiskUniform(GetSample(pixelCoord, _RaytracingSampleIndex, 106),
-                                                   GetSample(pixelCoord, _RaytracingSampleIndex, 107));
+    float2 uv = _PathTracingDoFParameters.x * SampleDiskUniform(GetSample(pixelCoord, _RaytracingSampleIndex, 106),
+                                                                GetSample(pixelCoord, _RaytracingSampleIndex, 107));
 
     // Compute the focus point by intersecting the pinhole ray with the focus plane
-    float focusDistance = _PathTracedDoFConstants.y;
-    float t = focusDistance / dotDirection;
+    float t = _PathTracingDoFParameters.y / dotDirection;
     float3 focusPoint = origin + t * direction;
 
     // Compute the new ray origin (_ViewMatrix[0] = right, _ViewMatrix[1] = up)
@@ -120,10 +117,15 @@ void RayGen()
     // Get the current pixel coordinates
     uint2 pixelCoord = DispatchRaysIndex().xy;
 
+    // Get the current tile coordinates (for interleaved tiling) and update pixel coordinates accordingly
+    uint2 tileCount = uint2(_PathTracingTilingParameters.xy);
+    uint2 tileIndex = uint2(_PathTracingTilingParameters.zw);
+    uint2 tiledPixelCoord = pixelCoord * tileCount + tileIndex;
+
     // Jitter them (we use 4x10 dimensions of our sequence during path tracing atm, so pick the next available ones)
     float4 jitteredPixelCoord = float4(pixelCoord, 1.0, 1.0);
-    jitteredPixelCoord.x += GetSample(pixelCoord, _RaytracingSampleIndex, 40);
-    jitteredPixelCoord.y += GetSample(pixelCoord, _RaytracingSampleIndex, 41);
+    jitteredPixelCoord.x += GetSample(tiledPixelCoord, _RaytracingSampleIndex, 40) / tileCount.x;
+    jitteredPixelCoord.y += GetSample(tiledPixelCoord, _RaytracingSampleIndex, 41) / tileCount.y;
 
     // Create the ray descriptor for this pixel
     RayDesc ray;
@@ -143,7 +145,7 @@ void RayGen()
         float dotDirection = dot(cameraDirection, ray.Direction);
         ray.TMin /= dotDirection;
 
-        ApplyDepthOfField(pixelCoord, dotDirection, ray.Origin, ray.Direction);
+        ApplyDepthOfField(tiledPixelCoord, dotDirection, ray.Origin, ray.Direction);
     }
     else // Orthographic projection
     {
@@ -156,16 +158,16 @@ void RayGen()
         ray.Direction = cameraDirection;
     }
 
-    // Create and init the PathIntersection structure for this
+    // Create and init the PathIntersection structure for this pixel
     PathIntersection pathIntersection;
     pathIntersection.value = 1.0;
     pathIntersection.alpha = 1.0;
     pathIntersection.remainingDepth = _RaytracingMaxRecursion;
-    pathIntersection.pixelCoord = pixelCoord;
+    pathIntersection.pixelCoord = tiledPixelCoord;
     pathIntersection.maxRoughness = 0.0;
 
     // In order to achieve filtering for the textures, we need to compute the spread angle of the pixel
-    pathIntersection.cone.spreadAngle = _RaytracingPixelSpreadAngle;
+    pathIntersection.cone.spreadAngle = _RaytracingPixelSpreadAngle / min(tileCount.x, tileCount.y);
     pathIntersection.cone.width = 0.0;
 
     // Evaluate the ray intersection