Fixed a performance issue with stochastic ray traced area shadows. (#300)

Co-authored-by: sebastienlagarde <[email protected]>

Author: anisunity

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

@@ -570,6 +570,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Made more explicit the warning about raytracing and asynchronous compute. Also fixed the condition in which it appears.
 - Fixed a null ref exception in static sky when the default volume profile is invalid.
 - Fixed issue with screen-space shadows not enabled properly when RT is disabled (case 1235821)
+- Fixed a performance issue with stochastic ray traced area shadows.
 
 ### Changed
 - Improve MIP selection for decals on Transparents

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

@@ -1,7 +1,11 @@
+// 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)
+	float denom = dot(normal, ray_dir);
+	if (abs(denom) > PLANE_INTERSECTION_EPSILON)
 	{ 
 	    float3 d = pos - ray_origin;
 	    t = dot(d, normal) / denom;