fix: #573 (part 2) NetworkManager detects additive scene loads and re…

…spawns objects on server/client again

Assets/Mirror/Runtime/NetworkManager.cs

@@ -82,6 +82,9 @@ public virtual void Awake()
             networkSceneName = offlineScene;
 
             InitializeSingleton();
+
+            // setup OnSceneLoaded callback
+            SceneManager.sceneLoaded += OnSceneLoaded;
         }
 
         // headless mode detection
@@ -146,6 +149,33 @@ public virtual void Start()
             }
         }
 
+        // support additive scene loads:
+        //   NetworkScenePostProcess disables all scene objects on load, and
+        //   * NetworkServer.SpawnObjects enables them again on the server when
+        //     calling OnStartServer
+        //   * ClientScene.PrepareToSpawnSceneObjects enables them again on the
+        //     client after the server sends ObjectSpawnStartedMessage to client
+        //     in SpawnObserversForConnection. this is only called when the
+        //     client joins, so we need to rebuild scene objects manually again
+        // TODO merge this with FinishLoadScene()?
+        void OnSceneLoaded(Scene scene, LoadSceneMode mode)
+        {
+            if (mode == LoadSceneMode.Additive)
+            {
+                if (NetworkServer.active)
+                {
+                    // TODO only respawn the server objects from that scene later!
+                    NetworkServer.SpawnObjects();
+                    Debug.Log("Respawned Server objects after additive scene load: " + scene.name);
+                }
+                if (NetworkClient.active)
+                {
+                    ClientScene.PrepareToSpawnSceneObjects();
+                    Debug.Log("Rebuild Client spawnableObjects after additive scene load: " + scene.name);
+                }
+            }
+        }
+
         // NetworkIdentity.UNetStaticUpdate is called from UnityEngine while LLAPI network is active.
         // if we want TCP then we need to call it manually. probably best from NetworkManager, although this means
         // that we can't use NetworkServer/NetworkClient without a NetworkManager invoking Update anymore.