Fix Asymmetric Projection Matrices and Fog / Pathtracing

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

@@ -268,6 +268,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed custom pass volume not executed in scene view because of the volume culling mask.
 - Fixed remapping of depth pyramid debug view
 - Fix wobbling/tearing-like artifacts with SSAO.
+- Fixed an issue with asymmetric projection matrices and fog / pathtracing. (case 1330290).
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard

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

@@ -1748,14 +1748,24 @@ Matrix4x4 GetJitteredProjectionMatrix(Matrix4x4 origProj)
         Matrix4x4 ComputePixelCoordToWorldSpaceViewDirectionMatrix(ViewConstants viewConstants, Vector4 resolution, float aspect = -1)
         {
             // In XR mode, use a more generic matrix to account for asymmetry in the projection
-            if (xr.enabled)
+            var useGenericMatrix = xr.enabled;
+
+            // Asymmetry is also possible from a user-provided projection, so we must check for it too.
+            // Note however, that in case of physical camera, the lens shift term is the only source of
+            // asymmetry, and this is accounted for in the optimized path below. Additionally, Unity C++ will
+            // automatically disable physical camera when the projection is overridden by user.
+            useGenericMatrix |= HDUtils.IsProjectionMatrixAsymmetric(viewConstants.projMatrix) && !camera.usePhysicalProperties;
+
+            if (useGenericMatrix)
             {
-                var transform = Matrix4x4.Scale(new Vector3(-1.0f, -1.0f, -1.0f)) * viewConstants.invViewProjMatrix;
-                transform = transform * Matrix4x4.Scale(new Vector3(1.0f, -1.0f, 1.0f));
-                transform = transform * Matrix4x4.Translate(new Vector3(-1.0f, -1.0f, 0.0f));
-                transform = transform * Matrix4x4.Scale(new Vector3(2.0f * resolution.z, 2.0f * resolution.w, 1.0f));
+                var viewSpaceRasterTransform = new Matrix4x4(
+                    new Vector4(2.0f * resolution.z, 0.0f, 0.0f, -1.0f),
+                    new Vector4(0.0f, -2.0f * resolution.w, 0.0f, 1.0f),
+                    new Vector4(0.0f, 0.0f, 1.0f, 0.0f),
+                    new Vector4(0.0f, 0.0f, 0.0f, 1.0f));
 
-                return transform.transpose;
+                var transformT = viewConstants.invViewProjMatrix.transpose * Matrix4x4.Scale(new Vector3(-1.0f, -1.0f, -1.0f));
+                return viewSpaceRasterTransform * transformT;
             }
 
             float verticalFoV = camera.GetGateFittedFieldOfView() * Mathf.Deg2Rad;

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

@@ -99,12 +99,12 @@ void RayGen()
     uint2 currentPixelCoord = uint2(LaunchIndex.x, LaunchIndex.y);
 
     // Jitter them (we use 4x10 dimensions of our sequence during path tracing atm, so pick the next available ones)
-    float3 jitteredPixelCoord = float3(currentPixelCoord, 1.0);
+    float4 jitteredPixelCoord = float4(currentPixelCoord, 1.0, 1.0);
     jitteredPixelCoord.x += GetSample(currentPixelCoord, _RaytracingSampleIndex, 40);
     jitteredPixelCoord.y += GetSample(currentPixelCoord, _RaytracingSampleIndex, 41);
 
-    // Compute the ray direction from those coordinates (for zero aperture)
-    float3 directionWS = -normalize(mul(jitteredPixelCoord, (float3x3)_PixelCoordToViewDirWS));
+    // Compute the ray direction from those coordinates (for zero aperture
+    float3 directionWS = -normalize(mul(jitteredPixelCoord, _PixelCoordToViewDirWS).xyz);
     float3 cameraPosWS = GetPrimaryCameraPosition();
 
     float apertureRadius = _PathTracedDoFConstants.x;

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

@@ -132,6 +132,14 @@ internal static int GetRuntimeDebugPanelWidth(HDCamera hdCamera)
         internal static float ProjectionMatrixAspect(in Matrix4x4 matrix)
             => - matrix.m11 / matrix.m00;
 
+        /// <summary>
+        /// Determine if a projection matrix is off-center (asymmetric).
+        /// </summary>
+        /// <param name="matrix"></param>
+        /// <returns></returns>
+        internal static bool IsProjectionMatrixAsymmetric(in Matrix4x4 matrix)
+            => matrix.m02 != 0 || matrix.m12 != 0;
+
         internal static Matrix4x4 ComputePixelCoordToWorldSpaceViewDirectionMatrix(float verticalFoV, Vector2 lensShift, Vector4 screenSize, Matrix4x4 worldToViewMatrix, bool renderToCubemap, float aspectRatio = -1, bool isOrthographic = false)
         {
             Matrix4x4 viewSpaceRasterTransform;