fix(core): improve accuracy of NetworkTime and smear changes on resync. (#228)

Author: pkaminski

MLAPI-Editor/NetworkingManagerEditor.cs

@@ -32,6 +32,7 @@ public class NetworkingManagerEditor : Editor
     private SerializedProperty connectionApprovalProperty;
     private SerializedProperty secondsHistoryProperty;
     private SerializedProperty enableTimeResyncProperty;
+    private SerializedProperty timeResyncIntervalProperty;
     private SerializedProperty enableNetworkedVarProperty;
     private SerializedProperty ensureNetworkedVarLengthSafetyProperty;
     private SerializedProperty forceSamePrefabsProperty;
@@ -108,6 +109,7 @@ private void Init()
         connectionApprovalProperty = networkConfigProperty.FindPropertyRelative("ConnectionApproval");
         secondsHistoryProperty = networkConfigProperty.FindPropertyRelative("SecondsHistory");
         enableTimeResyncProperty = networkConfigProperty.FindPropertyRelative("EnableTimeResync");
+        timeResyncIntervalProperty = networkConfigProperty.FindPropertyRelative("TimeResyncInterval");
         enableNetworkedVarProperty = networkConfigProperty.FindPropertyRelative("EnableNetworkedVar");
         ensureNetworkedVarLengthSafetyProperty = networkConfigProperty.FindPropertyRelative("EnsureNetworkedVarLengthSafety");
         forceSamePrefabsProperty = networkConfigProperty.FindPropertyRelative("ForceSamePrefabs");
@@ -144,6 +146,7 @@ private void CheckNullProperties()
         connectionApprovalProperty = networkConfigProperty.FindPropertyRelative("ConnectionApproval");
         secondsHistoryProperty = networkConfigProperty.FindPropertyRelative("SecondsHistory");
         enableTimeResyncProperty = networkConfigProperty.FindPropertyRelative("EnableTimeResync");
+        timeResyncIntervalProperty = networkConfigProperty.FindPropertyRelative("TimeResyncInterval");
         enableNetworkedVarProperty = networkConfigProperty.FindPropertyRelative("EnableNetworkedVar");
         ensureNetworkedVarLengthSafetyProperty = networkConfigProperty.FindPropertyRelative("EnsureNetworkedVarLengthSafety");
         forceSamePrefabsProperty = networkConfigProperty.FindPropertyRelative("ForceSamePrefabs");
@@ -277,7 +280,8 @@ public override void OnInspectorGUI()
             }
 
             EditorGUILayout.PropertyField(enableTimeResyncProperty);
-            
+            EditorGUILayout.PropertyField(timeResyncIntervalProperty);
+
             EditorGUILayout.LabelField("Performance", EditorStyles.boldLabel);
             EditorGUILayout.PropertyField(receiveTickrateProperty);
             EditorGUILayout.PropertyField(maxReceiveEventsPerTickRateProperty);

MLAPI/Configuration/NetworkConfig.cs

@@ -96,6 +96,11 @@ public class NetworkConfig
         [Tooltip("Enable this to resync the NetworkedTime after the initial sync")]
         public bool EnableTimeResync = false;
         /// <summary>
+        /// If time resync is turned on, this specifies the interval between syncs in seconds.
+        /// </summary>
+        [Tooltip("The amount of seconds between resyncs of NetworkedTime, if enabled")]
+        public int TimeResyncInterval = 30;
+        /// <summary>
         /// Whether or not to enable the NetworkedVar system. This system runs in the Update loop and will degrade performance, but it can be a huge convenience.
         /// Only turn it off if you have no need for the NetworkedVar system.
         /// </summary>

MLAPI/Core/NetworkingManager.cs

@@ -32,9 +32,12 @@ namespace MLAPI
     public class NetworkingManager : MonoBehaviour
     {
         /// <summary>
-        /// A syncronized time, represents the time in seconds since the server application started. Is replicated across all clients
+        /// A synchronized time, represents the time in seconds since the server application started. Is replicated across all clients
         /// </summary>
-        public float NetworkTime { get; internal set; }
+        public float NetworkTime => Time.unscaledTime + currentNetworkTimeOffset;
+        private float networkTimeOffset;
+        private float currentNetworkTimeOffset;
+        private bool networkTimeInitialized;
         /// <summary>
         /// Gets or sets if the NetworkingManager should be marked as DontDestroyOnLoad
         /// </summary>
@@ -297,7 +300,9 @@ private void Init(bool server)
             if (LogHelper.CurrentLogLevel <= LogLevel.Developer) LogHelper.LogInfo("Init()");
 
             LocalClientId = 0;
-            NetworkTime = 0f;
+            networkTimeOffset = 0f;
+            currentNetworkTimeOffset = 0f;
+            networkTimeInitialized = false;
             lastSendTickTime = 0f;
             lastEventTickTime = 0f;
             lastReceiveTickTime = 0f;
@@ -733,19 +738,35 @@ private void Update()
                     NetworkProfiler.EndTick();
                 }
 
-                if (IsServer && NetworkConfig.EnableTimeResync && NetworkTime - lastTimeSyncTime >= 30)
+                if (IsServer && NetworkConfig.EnableTimeResync && NetworkTime - lastTimeSyncTime >= NetworkConfig.TimeResyncInterval)
                 {
                     NetworkProfiler.StartTick(TickType.Event);
                     SyncTime();
                     lastTimeSyncTime = NetworkTime;
                     NetworkProfiler.EndTick();
                 }
 
-                NetworkTime += Time.unscaledDeltaTime;
+                if (!Mathf.Approximately(networkTimeOffset, currentNetworkTimeOffset)) {
+                    // Smear network time adjustments by no more than 200ms per second.  This should help code deal with
+                    // changes more gracefully, since the network time will always flow forward at a reasonable pace.
+                    float maxDelta = Mathf.Max(0.001f, 0.2f * Time.unscaledDeltaTime);
+                    currentNetworkTimeOffset += Mathf.Clamp(networkTimeOffset - currentNetworkTimeOffset, -maxDelta, maxDelta);
+                }
             }
         }
 
-        internal void SendConnectionRequest()
+        internal void UpdateNetworkTime(ulong clientId, float netTime)
+        {
+            float rtt = NetworkConfig.NetworkTransport.GetCurrentRtt(clientId) / 1000f;
+            networkTimeOffset = netTime - Time.realtimeSinceStartup + rtt / 2f;
+            if (!networkTimeInitialized) {
+                currentNetworkTimeOffset = networkTimeOffset;
+                networkTimeInitialized = true;
+            }
+            if (LogHelper.CurrentLogLevel <= LogLevel.Developer) LogHelper.LogInfo($"Received network time {netTime}, RTT to server is {rtt}, setting offset to {networkTimeOffset} (delta {networkTimeOffset - currentNetworkTimeOffset})");
+    }
+
+    internal void SendConnectionRequest()
         {
             using (PooledBitStream stream = PooledBitStream.Get())
             {
@@ -997,8 +1018,8 @@ private void SyncTime()
             {
                 using (PooledBitWriter writer = PooledBitWriter.Get(stream))
                 {
-                    writer.WriteSinglePacked(NetworkTime);
-                    InternalMessageSender.Send(MLAPIConstants.MLAPI_TIME_SYNC, "MLAPI_TIME_SYNC", stream, SecuritySendFlags.None, null);
+                    writer.WriteSinglePacked(Time.realtimeSinceStartup);
+                    InternalMessageSender.Send(MLAPIConstants.MLAPI_TIME_SYNC, "MLAPI_TIME_SYNC", stream, SecuritySendFlags.None, null, true);
                 }
             }
         }
@@ -1049,7 +1070,7 @@ internal void HandleApproval(ulong clientId, ulong? prefabHash, bool approved, V
                         writer.WriteUInt32Packed(NetworkSceneManager.currentSceneIndex);
                         writer.WriteByteArray(NetworkSceneManager.currentSceneSwitchProgressGuid.ToByteArray());
 
-                        writer.WriteSinglePacked(NetworkTime);
+                        writer.WriteSinglePacked(Time.realtimeSinceStartup);
 
                         writer.WriteUInt32Packed((uint)_observedObjects.Count);
 

MLAPI/Messaging/InternalMessageHandler.cs

@@ -206,9 +206,7 @@ internal static void HandleConnectionApproved(ulong clientId, Stream stream)
                 Guid sceneSwitchProgressGuid = new Guid(reader.ReadByteArray());
 
                 float netTime = reader.ReadSinglePacked();
-                ulong msDelay = NetworkingManager.Singleton.NetworkConfig.NetworkTransport.GetCurrentRtt(clientId);
-                
-                NetworkingManager.Singleton.NetworkTime = netTime + (msDelay / 1000f);
+                NetworkingManager.Singleton.UpdateNetworkTime(clientId, netTime);
 
                 NetworkingManager.Singleton.ConnectedClients.Add(NetworkingManager.Singleton.LocalClientId, new NetworkedClient() { ClientId = NetworkingManager.Singleton.LocalClientId });
 
@@ -430,9 +428,7 @@ internal static void HandleTimeSync(ulong clientId, Stream stream)
             using (PooledBitReader reader = PooledBitReader.Get(stream))
             {
                 float netTime = reader.ReadSinglePacked();
-                ulong msDelay = NetworkingManager.Singleton.NetworkConfig.NetworkTransport.GetCurrentRtt(clientId);
-                
-                NetworkingManager.Singleton.NetworkTime = netTime + (msDelay / 1000f);
+                NetworkingManager.Singleton.UpdateNetworkTime(clientId, netTime);
             }
         }
 
@@ -644,5 +640,6 @@ internal static void HandleCustomMessage(ulong clientId, Stream stream)
         {
             NetworkingManager.Singleton.InvokeOnIncomingCustomMessage(clientId, stream);
         }
+
     }
 }

MLAPI/Messaging/InternalMessageSender.cs

@@ -33,7 +33,7 @@ internal static void Send(ulong clientId, byte messageType, string channelName,
             }
         }
 
-        internal static void Send(byte messageType, string channelName, BitStream messageStream, SecuritySendFlags flags, NetworkedObject targetObject)
+        internal static void Send(byte messageType, string channelName, BitStream messageStream, SecuritySendFlags flags, NetworkedObject targetObject, bool skipQueue = false)
         {
             bool encrypted = ((flags & SecuritySendFlags.Encrypted) == SecuritySendFlags.Encrypted) && NetworkingManager.Singleton.NetworkConfig.EnableEncryption;
             bool authenticated = ((flags & SecuritySendFlags.Authenticated) == SecuritySendFlags.Authenticated) && NetworkingManager.Singleton.NetworkConfig.EnableEncryption;
@@ -63,7 +63,7 @@ internal static void Send(byte messageType, string channelName, BitStream messag
                             continue;
                         }
 
-                        NetworkingManager.Singleton.NetworkConfig.NetworkTransport.Send(NetworkingManager.Singleton.ConnectedClientsList[i].ClientId, new ArraySegment<byte>(stream.GetBuffer(), 0, (int)stream.Length), channelName, false);
+                        NetworkingManager.Singleton.NetworkConfig.NetworkTransport.Send(NetworkingManager.Singleton.ConnectedClientsList[i].ClientId, new ArraySegment<byte>(stream.GetBuffer(), 0, (int)stream.Length), channelName, skipQueue);
                     }
                     NetworkProfiler.EndEvent();
                 }