Game.ChangeScene shows a loading screen for all clients instead of just the host

Author: CarsonKompon

engine/Sandbox.Engine/Game/Game/Game.Scene.cs

@@ -35,6 +35,10 @@ public static bool ChangeScene( SceneLoadOptions options )
 		if ( !Networking.IsHost )
 			return false;
 
+		// Tell clients the host is about to load a new scene before we start,
+		// so we show a loading screen immediately rather than freezing silently.
+		SceneNetworkSystem.Instance?.NotifySceneChangeStarting( options );
+
 		// We don't want to send any networked messages to do with deletion or creation
 		// of GameObjects here. Because the client will destroy their scene locally
 		// anyway. This saves us sending a message for potentially 100s of objects.

engine/Sandbox.Engine/Scene/Networking/SceneNetworkSystem.cs

@@ -46,6 +46,7 @@ internal SceneNetworkSystem( Internal.TypeLibrary typeLibrary, NetworkSystem sys
 		AddHandler<SceneRpcMsg>( OnSceneRpc );
 		AddHandler<StaticRpcMsg>( OnStaticRpc );
 		AddHandler<LoadSceneBeginMsg>( OnLoadSceneMsg );
+		AddHandler<LoadSceneNotifyMsg>( OnLoadSceneNotifyMsg );
 		AddHandler<LoadSceneSnapshotMsg>( OnLoadSceneSnapshotMsg );
 		AddHandler<LoadSceneRequestSnapshotMsg>( OnLoadSceneRequestSnapshotMsg );
 		AddHandler<SceneLoadedMsg>( OnSceneLoadedMsg );
@@ -84,6 +85,35 @@ internal static IDisposable SuppressDestroyMessages()
 
 	private readonly Dictionary<Guid, Guid> PendingSceneLoads = new();
 
+	/// <summary>
+	/// Notify all connected clients that the host is loading a new scene.
+	/// Sent before <see cref="LoadSceneBroadcast"/> so clients can show a loading screen immediately rather than freezing with no feedback.
+	/// </summary>
+	internal void NotifySceneChangeStarting( SceneLoadOptions options )
+	{
+		if ( !Networking.IsActive || !Networking.IsHost )
+			return;
+
+		var msg = new LoadSceneNotifyMsg { ShowLoadingScreen = options.ShowLoadingScreen };
+
+		var bs = ByteStream.Create( 64 );
+		bs.Write( InternalMessageType.Packed );
+		Networking.System.Serialize( msg, ref bs );
+
+		foreach ( var c in Connection.All )
+		{
+			if ( c == Connection.Local )
+				continue;
+
+			if ( c.State < Connection.ChannelState.Snapshot )
+				continue;
+
+			c.SendStream( bs );
+		}
+
+		bs.Dispose();
+	}
+
 	/// <summary>
 	/// Load a scene for all other clients. This can only be called by the host.
 	/// </summary>
@@ -302,6 +332,21 @@ private async Task OnLoadSceneRequestSnapshotMsg( LoadSceneRequestSnapshotMsg ms
 		bs.Dispose();
 	}
 
+	/// <summary>
+	/// Called when the host notifies us it is about to begin loading a new scene.
+	/// </summary>
+	private void OnLoadSceneNotifyMsg( LoadSceneNotifyMsg msg, Connection connection, Guid msgId )
+	{
+		if ( Game.IsEditor )
+			return;
+
+		if ( msg.ShowLoadingScreen )
+		{
+			LoadingScreen.IsVisible = true;
+			LoadingScreen.Title = "Loading Scene";
+		}
+	}
+
 	/// <summary>
 	/// Called when the host has told us to load a new scene.
 	/// </summary>
@@ -1375,6 +1420,12 @@ struct ObjectRefreshMsg
 	public Guid Guid { get; set; }
 }
 
+[Expose]
+struct LoadSceneNotifyMsg
+{
+	public bool ShowLoadingScreen { get; set; }
+}
+
 [Expose]
 struct LoadSceneBeginMsg
 {