Update AutoSceneSwitcher.cs (#754)

Co-authored-by: Stephen Hodgson <hodgson.designs@gmail.com>

Editor/Utilities/AutoSceneSwitcher.cs

@@ -1,10 +1,12 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) XRTK. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
 using UnityEditor;
 using UnityEditor.Experimental.SceneManagement;
 using UnityEditor.SceneManagement;
 using UnityEngine.SceneManagement;
+using XRTK.Services;
+using XRTK.Extensions;
 using XRTK.Editor.Utilities.SymbolicLinks;
 
 namespace XRTK.Editor.Utilities
@@ -20,6 +22,9 @@ static AutoSceneSwitcher()
         {
             EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
 
+            // If a start scene hasn't been configured yet for XRTK but the project
+            // has build scenes configured, we assume the scene at index 0 of the build scenes
+            // is our start scene and save it to preferences, unless it's the Unity default sample scene.
             if (MixedRealityPreferences.StartSceneAsset == null &&
                 EditorBuildSettings.scenes.Length > 0 &&
                 !EditorBuildSettings.scenes[0].path.Contains("SampleScene"))
@@ -41,47 +46,65 @@ private static void OnPlayModeStateChanged(PlayModeStateChange playModeState)
             var startSceneAsset = MixedRealityPreferences.StartSceneAsset;
             var startSceneLoaded = false;
 
+            // If we have a start scene configured in the XRTK preferences
+            // make sure it's loaded.
             if (startSceneAsset != null)
             {
                 for (int i = 0; i < SceneManager.sceneCount; i++)
                 {
-                    var scene = SceneManager.GetSceneAt(i);
-
-                    if (scene.name == startSceneAsset.name &&
-                        SceneManager.GetActiveScene().name != startSceneAsset.name)
+                    var loadedScene = SceneManager.GetSceneAt(i);
+                    if (string.Equals(loadedScene.name, startSceneAsset.name))
                     {
-                        SceneManager.SetActiveScene(scene);
                         startSceneLoaded = true;
                         break;
                     }
                 }
 
+                // A start scene was configured in preferences, but it's not loaded
+                // into hierarchy yet, so we force load it for the user now.
                 if (!startSceneLoaded && startSceneAsset != null)
                 {
                     var startScene = EditorSceneManager.OpenScene(AssetDatabase.GetAssetOrScenePath(startSceneAsset), OpenSceneMode.Additive);
-                    SceneManager.SetActiveScene(startScene);
+
+                    // Move the start scene to be first in hierarchy, if multiples scenes are loaded.
+                    if (SceneManager.sceneCount > 1)
+                    {
+                        EditorSceneManager.MoveSceneBefore(startScene, SceneManager.GetSceneAt(1));
+                    }
+
+                    startSceneLoaded = true;
                 }
             }
 
-            if (startSceneAsset != null && SceneManager.GetActiveScene().name == startSceneAsset.name) { return; }
-
-            var dialogResult = EditorUtility.DisplayDialogComplex(
-                    title: "Missing the MixedRealityToolkit",
-                    message: "Would you like to configure the Mixed Reality Toolkit now?",
-                    "No, play anyway",
-                    "Configure, then play",
-                    "Cancel");
+            // If the start scene was successfully loaded, we're good and can continue playing.
+            if (startSceneLoaded)
+            {
+                return;
+            }
 
-            switch (dialogResult)
+            // We couldn't auto setup the XRTK start scene for the user. Thus, the currently
+            // loaded scene(s) may not contain a proper XRTK service locator game object configuration.
+            // Least we can do now is offer the user to auto configure the current scene, if none of the
+            // loaded scenes already contains a XRTK configuration.
+            if (MixedRealityToolkit.Instance.IsNull())
             {
-                case 1:
-                    MixedRealityToolkitInspector.CreateMixedRealityToolkitGameObject();
-                    EditorApplication.isPlaying = true;
-                    break;
-                case 2:
-                    EditorApplication.isPlaying = false;
-                    break;
+                var dialogResult = EditorUtility.DisplayDialogComplex(
+                        title: "Missing the MixedRealityToolkit",
+                        message: "Would you like to configure the Mixed Reality Toolkit now?",
+                        "No, play anyway",
+                        "Configure, then play",
+                        "Cancel");
+
+                switch (dialogResult)
+                {
+                    case 1:
+                        MixedRealityToolkitInspector.CreateMixedRealityToolkitGameObject();
+                        break;
+                    case 2:
+                        EditorApplication.isPlaying = false;
+                        break;
+                }
             }
         }
     }
-}
+}