[7.x.x Backport] Fixed a performance issue with stochastic ray traced area shadows.

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

@@ -62,6 +62,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed shadowmask UI now correctly showing shadowmask disable
 - Fixed the indirect diffuse texture not being ignored when it should (ray tracing disabled).
 - Fixed depth prepass and postpass being disabled after changing the shader in the material UI.
+- Fixed a performance issue with stochastic ray traced area shadows.
 
 ### Changed
 - Rejecting history for ray traced reflections based on a threshold evaluated on the neighborhood of the sampled history.

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/Shadows/SphericalQuad.hlsl

@@ -1,13 +1,17 @@
+// I am not sure why exactly, by a lower epsilon generates ray that even if they give a valid result with ray tracing
+// nuke the performance. Changing the epsilon from 1e-6 to 1e-5 seems to solve the issue.
+#define PLANE_INTERSECTION_EPSILON 1e-5
+
 bool IntersectPlane(float3 ray_origin, float3 ray_dir, float3 pos, float3 normal, out float t)
 {
-	float denom = dot(normal, ray_dir); 
-	if (abs(denom) > 1e-6)
-	{ 
-	    float3 d = pos - ray_origin;
-	    t = dot(d, normal) / denom;
-	    return (t >= 0); 
-	} 
-	return false; 
+    float denom = dot(normal, ray_dir); 
+    if (abs(denom) > PLANE_INTERSECTION_EPSILON)
+    { 
+        float3 d = pos - ray_origin;
+        t = dot(d, normal) / denom;
+        return (t >= 0); 
+    } 
+    return false; 
 }
 
 struct SphQuad
@@ -72,7 +76,7 @@ void SphQuadInit(float3 s, float3 ex, float3 ey, float3 o, inout SphQuad squad)
     squad.b0 = n0.z;
     squad.b1 = n2.z;
     squad.b0sq = squad.b0 * squad.b0;
-    squad.k = 2.0f * 	PI - g2 - g3;
+    squad.k = 2.0f * PI - g2 - g3;
 
     // compute solid angle from internal angles
     squad.S = g0 + g1 - squad.k;