[7.x.x Backport] Fix exposure white flash when enabling SSR (#845)

FrancescoC-unity · sebastienlagarde · web-flow · commit 6abf9cc56dbd · 2020-08-04T00:27:14.000+02:00
* inform postprocess

* Changelog

Co-authored-by: sebastienlagarde &lt;sebastien@unity3d.com&gt;
diff --git a/com.unity.render-pipelines.high-definition/CHANGELOG.md b/com.unity.render-pipelines.high-definition/CHANGELOG.md
@@ -1,4 +1,4 @@
-# Changelog
+﻿# Changelog
 All notable changes to this package will be documented in this file.
 
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - PBR Sky now doesn't go black when going below sea level, but it instead freezes calculation as if on the horizon.
 - Fixed XR single-pass macros in tessellation shaders.
 - Fixed XR Display providers not getting zNear and zFar plane distances passed to them when in HDRP.
+- Fixed issue with white flash when enabling SSR.
 
 ### Changed
 - Changed extensions of shader CAS include files.
diff --git a/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Camera/HDCamera.cs b/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Camera/HDCamera.cs
@@ -420,6 +420,8 @@ internal void Update(FrameSettings currentFrameSettings, HDRenderPipeline hdrp,
                     // Reinit the system.
                     colorPyramidHistoryIsValid = false;
                     volumetricHistoryIsValid = false;
+                    // Since we nuke all history we must inform the post process system too.
+                    resetPostProcessingHistory = true;
 
                     // The history system only supports the "nuke all" option.
                     m_HistoryRTSystem.Dispose();
