New tooltip for camera background and fixed exposure when switching the background mode.

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

@@ -598,6 +598,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed assert on tests caused by probe culling results being requested when culling did not happen. (case 1246169) 
 - Fixed over consumption of GPU memory by the Physically Based Sky.
 - Fixed an invalid rotation in Planar Reflection Probe editor display, that was causing an error message (case 1182022)
+- Put more information in Camera background type tooltip and fixed inconsistent exposure behavior when changing bg type.
 
 ### Changed
 - Improve MIP selection for decals on Transparents

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

@@ -264,6 +264,9 @@ internal HDAdditionalCameraData.ClearColorMode clearColorMode
             }
         }
 
+        HDAdditionalCameraData.ClearColorMode m_PreviousClearColorMode = HDAdditionalCameraData.ClearColorMode.None;
+
+
         internal Color backgroundColorHDR
         {
             get
@@ -505,7 +508,7 @@ internal void SetReferenceSize()
             RTHandles.SetReferenceSize(actualWidth, actualHeight, msaaSamples);
             m_HistoryRTSystem.SwapAndSetReferenceSize(actualWidth, actualHeight, msaaSamples);
         }
-        
+
         // Updating RTHandle needs to be done at the beginning of rendering (not during update of HDCamera which happens in batches)
         // The reason is that RTHandle will hold data necessary to setup RenderTargets and viewports properly.
         internal void BeginRender(CommandBuffer cmd)
@@ -888,9 +891,11 @@ 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;
             }
         }