feat: implement NetworkTickSystem based on NetworkUpdateLoop (#502)

Author: jeffreyrainy

com.unity.multiplayer.mlapi/Runtime/Core/NetworkTickSystem.cs

@@ -0,0 +1,84 @@
+using System;
+using UnityEngine;
+
+namespace MLAPI
+{
+    // todo: This is a pretty minimal tick system. It will be improved in the future
+    // It currently relies on Time.unscaledTime and, as such, will start suffering
+    // numerical precision issues after 2^23 ticks have passed (float have 23 bits mantissa)
+    // For future releases, we'll need to improve on this, probably by leveraging FixedUpdate
+
+    public class NetworkTickSystem : INetworkUpdateSystem, IDisposable
+    {
+        private const float k_DefaultTickIntervalSec = 1/60f; // Defaults to 60 ticks second
+        private float m_TickIntervalSec; // Duration of a tick in seconds
+        private int m_NetworkTickCount; // How many network ticks have passed?
+
+        private static NetworkTickSystem m_Instance = null;
+
+        // special value to indicate "No tick information"
+        public const ushort k_NoTick = ushort.MaxValue;
+        // Number of ticks over which the tick number wraps back to 0
+        public const ushort k_TickPeriod = k_NoTick - 1;
+
+        /// <summary>
+        /// Constructor
+        /// Defaults to k_DefaultTickIntervalSec if no tick duration is specified
+        /// </summary>
+        /// <param name="tickIntervalSec">Duration of a network tick</param>
+        public NetworkTickSystem(float tickIntervalSec = k_DefaultTickIntervalSec)
+        {
+            this.RegisterNetworkUpdate(NetworkUpdateStage.EarlyUpdate);
+
+            //Assure we don't specify a value less than or equal to zero for tick frequency
+            m_TickIntervalSec = (tickIntervalSec <= 0f) ? k_DefaultTickIntervalSec : tickIntervalSec;
+
+            // ticks might not start at 0, so let's update right away at construction
+            UpdateNetworkTick();
+        }
+
+        public void Dispose()
+        {
+            this.UnregisterNetworkUpdate(NetworkUpdateStage.EarlyUpdate);
+        }
+
+        /// <summary>
+        /// GetTick
+        /// Gets the current network tick (non-fractional, wrapping around)
+        /// </summary>
+        /// <returns></returns>
+        public ushort GetTick()
+        {
+            return (ushort)(m_NetworkTickCount % k_TickPeriod);
+        }
+
+        /// <summary>
+        /// GetNetworkTime
+        /// Network time is calculated from m_NetworkTickCount and m_TickIntervalSec (tick frequency)
+        /// </summary>
+        /// <returns>Network Time</returns>
+        public float GetNetworkTime()
+        {
+            return m_NetworkTickCount * m_TickIntervalSec;
+        }
+
+        /// <summary>
+        /// UpdateNetworkTick
+        /// Called each network loop update during the PreUpdate stage
+        /// </summary>
+        private void UpdateNetworkTick()
+        {
+            m_NetworkTickCount = (int)(Time.unscaledTime / m_TickIntervalSec);
+        }
+
+        public void NetworkUpdate(NetworkUpdateStage updateStage)
+        {
+            switch (updateStage)
+            {
+                case NetworkUpdateStage.EarlyUpdate:
+                    UpdateNetworkTick();
+                    break;
+            }
+        }
+    }
+}

com.unity.multiplayer.mlapi/Runtime/Core/NetworkTickSystem.cs.meta

@@ -71,6 +71,7 @@ public class NetworkingManager : MonoBehaviour, INetworkUpdateSystem
         static ProfilerMarker s_InvokeRPC = new ProfilerMarker("InvokeRPC");
 #endif
         internal RpcQueueContainer rpcQueueContainer { get; private set; }
+        internal NetworkTickSystem networkTickSystem { get; private set; }
 
         /// <summary>
         /// A synchronized time, represents the time in seconds since the server application started. Is replicated across all clients
@@ -383,6 +384,12 @@ private void Init(bool server)
                 return;
             }
 
+            //This 'if' should never enter
+            if (networkTickSystem != null)
+            {
+                networkTickSystem.Dispose();
+            }
+            networkTickSystem = new NetworkTickSystem();
 
             //This should never happen, but in the event that it does there should be (at a minimum) a unity error logged.
             if(rpcQueueContainer != null)
@@ -698,6 +705,12 @@ public void Shutdown()
                 rpcQueueContainer = null;
             }
 
+            if (networkTickSystem != null)
+            {
+                networkTickSystem.Dispose();
+            }
+            networkTickSystem = null;
+
             NetworkProfiler.Stop();
             IsListening = false;
             IsServer = false;