Backport of 2d/fix for self shadow

com.unity.render-pipelines.universal/CHANGELOG.md

@@ -4,6 +4,12 @@ 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/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+- Fixed an issue where ShadowCaster2Ds were sometimes being rendered twice in the editor while in playmode.
+
+
 ## [10.9.0] - 2021-12-06
 
 ### Fixed

com.unity.render-pipelines.universal/Runtime/2D/Shadows/ShadowCasterGroup2DManager.cs

@@ -2,15 +2,36 @@
 using System.Collections.Generic;
 using UnityEngine;
 
+#if UNITY_EDITOR
+using UnityEditor;
+#endif
+
 namespace UnityEngine.Experimental.Rendering.Universal
 {
+#if UNITY_EDITOR
+    [InitializeOnLoadAttribute]
+#endif
     internal class ShadowCasterGroup2DManager
     {
         static List<ShadowCasterGroup2D> s_ShadowCasterGroups = null;
 
         public static List<ShadowCasterGroup2D> shadowCasterGroups { get { return s_ShadowCasterGroups; } }
 
 
+#if UNITY_EDITOR
+        static ShadowCasterGroup2DManager()
+        {
+            EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
+        }
+
+        private static void OnPlayModeStateChanged(PlayModeStateChange state)
+        {
+            if (s_ShadowCasterGroups != null && (state == PlayModeStateChange.ExitingEditMode || state == PlayModeStateChange.ExitingPlayMode))
+                s_ShadowCasterGroups.Clear();
+        }
+
+#endif
+
         public static void AddShadowCasterGroupToList(ShadowCasterGroup2D shadowCaster, List<ShadowCasterGroup2D> list)
         {
             int positionToInsert = 0;