fix: Fixed NetworkVar assignment of the same value triggering replication (#1819)

Author: TwoTenPvP

com.unity.netcode.gameobjects/Runtime/NetworkVariable/NetworkVariable.cs

@@ -1,5 +1,7 @@
 using UnityEngine;
 using System;
+using System.Runtime.CompilerServices;
+using Unity.Collections.LowLevel.Unsafe;
 
 namespace Unity.Netcode
 {
@@ -87,6 +89,12 @@ public virtual T Value
             get => m_InternalValue;
             set
             {
+                // Compare bitwise
+                if (ValueEquals(ref m_InternalValue, ref value))
+                {
+                    return;
+                }
+
                 if (m_NetworkBehaviour && !CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
                 {
                     throw new InvalidOperationException("Client is not allowed to write to this NetworkVariable");
@@ -96,6 +104,21 @@ public virtual T Value
             }
         }
 
+        // Compares two values of the same unmanaged type by underlying memory
+        // Ignoring any overriden value checks
+        // Size is fixed
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static unsafe bool ValueEquals(ref T a, ref T b)
+        {
+            // get unmanaged pointers
+            var aptr = UnsafeUtility.AddressOf(ref a);
+            var bptr = UnsafeUtility.AddressOf(ref b);
+
+            // compare addresses
+            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(T)) == 0;
+        }
+
+
         private protected void Set(T value)
         {
             m_IsDirty = true;

com.unity.netcode.gameobjects/Tests/Editor/NetworkVar.meta

@@ -0,0 +1,41 @@
+using NUnit.Framework;
+
+namespace Unity.Netcode.EditorTests.NetworkVar
+{
+    public class NetworkVarTests
+    {
+        [Test]
+        public void TestAssignmentUnchanged()
+        {
+            var intVar = new NetworkVariable<int>();
+
+            intVar.Value = 314159265;
+
+            intVar.OnValueChanged += (value, newValue) =>
+            {
+                Assert.Fail("OnValueChanged was invoked when setting the same value");
+            };
+
+            intVar.Value = 314159265;
+        }
+
+        [Test]
+        public void TestAssignmentChanged()
+        {
+            var intVar = new NetworkVariable<int>();
+
+            intVar.Value = 314159265;
+
+            var changed = false;
+
+            intVar.OnValueChanged += (value, newValue) =>
+            {
+                changed = true;
+            };
+
+            intVar.Value = 314159266;
+
+            Assert.True(changed);
+        }
+    }
+}