[HDRP] Fix issue with path tracing when switching between non-persistent cameras (#5246)

* Fix issue with path traceing accumulation when switching between cameras.

* Check if camera history is persistent

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

Author: pmavridis

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

@@ -335,6 +335,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed some of the extreme ghosting in DLSS by using a bit mask to bias the color of particles. VFX tagged as Exclude from TAA will be on this pass.
 - Fixed update order in Graphics Compositor causing jumpy camera updates (case 1345566).
 - Fixed material inspector that allowed setting intensity to an infinite value.
+- Fixed issue when switching between non-persistent cameras when path tarcing is enabled (case 1337843).
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard

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

@@ -361,6 +361,13 @@ TextureHandle RenderPathTracing(RenderGraph renderGraph, HDCamera hdCamera, Text
             int camID = hdCamera.camera.GetInstanceID();
             CameraData camData = m_SubFrameManager.GetCameraData(camID);
 
+            // Check if the camera has a valid history buffer and if not reset the accumulation.
+            // This can happen if a script disables and re-enables the camera (case 1337843).
+            if (!hdCamera.isPersistent && hdCamera.GetCurrentFrameRT((int)HDCameraFrameHistoryType.PathTracing) == null)
+            {
+                m_SubFrameManager.Reset(camID);
+            }
+
             if (!m_SubFrameManager.isRecording)
             {
                 // Check if things have changed and if we need to restart the accumulation