[Backport 8.x.x] New tooltip for camera background and fixed exposure when switching the background mode.

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

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed some GCAlloc in the debug window.
 - Removed logic in the UI to disable parameters for contact shadows and fog volume components as it was going against the concept of the volume system.
 - Fixed over consumption of GPU memory by the Physically Based Sky.
+- Put more information in Camera background type tooltip and fixed inconsistent exposure behavior when changing bg type.
 
 ### Changed
 - Shadowmask and realtime reflection probe property are hide in Quality settings

com.unity.render-pipelines.high-definition/Editor/RenderPipeline/Camera/HDCameraUI.Skin.cs

@@ -13,7 +13,7 @@ static partial class HDCameraUI
 
         const string msaaWarningMessage = "Manual MSAA target set with deferred rendering. This will lead to undefined behavior.";
 
-        static readonly GUIContent clearModeContent = EditorGUIUtility.TrTextContent("Background Type", "Specifies the type of background the Camera applies when it clears the screen before rendering a frame.");
+        static readonly GUIContent clearModeContent = EditorGUIUtility.TrTextContent("Background Type", "Specifies the type of background the Camera applies when it clears the screen before rendering a frame. Be aware that when setting this to None, the background is never cleared and since HDRP shares render texture between cameras, you may end up with garbage from previous rendering.");
         static readonly GUIContent backgroundColorContent = EditorGUIUtility.TrTextContent("Background Color", "The Background Color used to clear the screen when selecting Background Color before rendering.");
         static readonly GUIContent cullingMaskContent = EditorGUIUtility.TrTextContent("Culling Mask");
         static readonly GUIContent volumeLayerMaskContent = EditorGUIUtility.TrTextContent("Volume Layer Mask");

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

@@ -256,6 +256,9 @@ internal HDAdditionalCameraData.ClearColorMode clearColorMode
             }
         }
 
+        HDAdditionalCameraData.ClearColorMode m_PreviousClearColorMode = HDAdditionalCameraData.ClearColorMode.None;
+
+
         internal Color backgroundColorHDR
         {
             get
@@ -880,9 +883,11 @@ void UpdateAntialiasing()
             }
 
             // When changing antialiasing mode to TemporalAA we must reset the history, otherwise we get one frame of garbage
-            if (previousAntialiasing != antialiasing && antialiasing == AntialiasingMode.TemporalAntialiasing)
+            if ( (previousAntialiasing != antialiasing && antialiasing == AntialiasingMode.TemporalAntialiasing)
+                || (m_PreviousClearColorMode != clearColorMode))
             {
                 resetPostProcessingHistory = true;
+                m_PreviousClearColorMode = clearColorMode;
             }
         }