Changed the behavior the max ray length for recursive rendering to match RTR and rasterization. (#6643)

* Changed the behavior the max ray length for recursive rendering to match RTR and rasterization.

* Update documentation

Author: anisunity

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

@@ -101,6 +101,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Replaced the geometry distance offset in the Probe Volume component by a minimum renderer volume threshold to ignore small objects when placing probes.
 - Small improvement changes in the UX for the Unlit Distortion field.
 - Improvements done to the water system (Deferred, Decals, SSR, Foam, Caustics, etc.).
+- Changed the behavior the max ray length for recursive rendering to match RTR and rasterization.
 
 ## [13.1.2] - 2021-11-05
 

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

@@ -39,7 +39,7 @@ Since recursive rendering uses an independent render pass, HDRP cannot render an
 | -------------- | ------------------------------------------------------------ |
 | **LayerMask**  | Defines the layers that HDRP processes this ray-traced effect for. |
 | **Max Depth**  | Controls the maximum number of times a ray can reflect or refract before it stops and returns the final color. Increasing this value increases execution time exponentially. |
-| **Max Ray Length** | Controls the length of the rays that HDRP uses for ray tracing. If a ray doesn't find an intersection, then the ray returns the color of the sky. |
+| **Max Ray Length** | Controls the length of the rays that HDRP uses for ray tracing after the initial intersection. For the primary ray, HDRP uses the camera's near and far planes.|
 | **Min Smoothness** | Defines the threshold at which reflection rays are not cast if the smoothness value of the target surface is inferior to the one defined by the parameter. |
 | **Ray Miss**                  | Determines what HDRP does when recursive rendering doesn't find an intersection. Choose from one of the following options: <br/>&#8226;**Reflection probes**: HDRP uses reflection probes in your scene to calculate the last recursive rendering bounce.<br/>&#8226;**Sky**: HDRP uses the sky defined by the current [Volume](Volumes.md) settings to calculate the last recursive rendering bounce.<br/>&#8226;**Both** : HDRP uses both reflection probes and the sky defined by the current [Volume](Volumes.md) settings to calculate the last recursive rendering bounce.<br/>&#8226;**Nothing**: HDRP does not calculate indirect lighting when recursive rendering doesn't find an intersection.<br/><br/>This property is set to **Both** by default. |
 | **Last Bounce**               | Determines what HDRP does when recursive rendering lights the last bounce. Choose from one of the following options: <br/>&#8226;**Reflection probes**: HDRP uses reflection probes in your scene to calculate the last bounce.<br/>&#8226;**Sky**: HDRP uses the sky defined by the current [Volume](Volumes.md) settings to calculate the last recursive rendering bounce.<br/>&#8226;**Both**:  HDRP uses both reflection probes and the sky defined by the current [Volume](Volumes.md) settings to calculate the last recursive rendering bounce.<br/>&#8226;**Nothing**: HDRP does not calculate indirect lighting when it evaluates the last bounce.<br/><br/>This property is set to **Both** by default. |

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/Shaders/RaytracingRenderer.raytrace

@@ -95,8 +95,11 @@ void RayGenRenderer()
 	RayDesc rayDescriptor;
 	rayDescriptor.Origin = originWS;
 	rayDescriptor.Direction = incidentWS;
-	rayDescriptor.TMin = _RaytracingCameraNearPlane;
-	rayDescriptor.TMax = _RaytracingRayMaxLength;
+
+	// For the initial ray, we don't want to have any disparity between the rasterization and ray tracing (which objects are rendered)
+	// thus we need to force the max distance to the far plane.
+	rayDescriptor.TMin = _ProjectionParams.y;
+	rayDescriptor.TMax = _ProjectionParams.z;
 
 	// Adjust world-space position to match the RAS setup with XR single-pass and camera relative
 	ApplyCameraRelativeXR(rayDescriptor.Origin);