fix: host client SyncVar hooks ignoring AOI visibility (#4079)

Copilot · MrGadget1024 · web-flow · commit 81d53df55a95 · 2026-01-12T09:32:30.000+01:00
* Initial plan

* Fix host client SyncVar hook AOI bugs

- Modified GeneratedSyncVarSetter methods to only call hooks in host mode if object is visible (in NetworkClient.spawned)
- Modified OnHostClientSpawn to deserialize spawn payload, triggering SyncVar hooks when objects enter AOI range
- This fixes both issues: hooks no longer fire at spawn for out-of-range objects, and hooks now fire when entering range

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Replace placeholder issue numbers with descriptive text

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Fix comment capitalization per code review

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Fix regression: restore SyncVar hooks in host mode with AOI

Previous fix prevented all SyncVar hooks from firing by checking NetworkClient.spawned too early.
The check happened when the value was set on the server, before the object was added to spawned.

New approach:
- Revert setter checks to allow hooks during server-side value assignment
- Add hostInitialSpawn flag to NetworkIdentity
- Set flag in OnHostClientSpawn before deserializing
- Modify all GeneratedSyncVarDeserialize methods to force hooks during initial spawn even if value unchanged
- Clear flag after deserialization

This ensures hooks fire when objects enter AOI range in host mode, addressing the original issue without breaking normal hook execution.

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Fix issue 1: prevent hooks from firing at spawn for out-of-range objects

Added NetworkClient.spawned.ContainsKey() check to all four GeneratedSyncVarSetter methods.
This prevents hooks from firing when SyncVars are set during OnStartServer() for objects not yet visible to host client.

Combined with the hostInitialSpawn flag (which forces hooks during deserialization when entering AOI),
this now fixes both issues:
- Issue 1: No hooks fire at spawn for out-of-range objects
- Issue 2: Hooks fire when objects enter AOI range

The check works because objects are added to NetworkClient.spawned in OnHostClientSpawn BEFORE deserialization,
so the deserialize path can fire hooks while the setter path is blocked for invisible objects.

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Fix unit tests: only check hostInitialSpawn in actual host mode

Added NetworkServer.activeHost check before using hostInitialSpawn flag in all four GeneratedSyncVarDeserialize methods.
This prevents the flag from being checked in non-host mode tests, which was causing NullReferenceExceptions when hooks were called during deserialization even though values hadn't changed.

The hostInitialSpawn flag should only force hooks in host mode. In regular client mode, hooks should only fire when values actually change.

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* Fix host mode tests: only force hooks when AOI is active

Changed hostInitialSpawn flag to only be set when aoi != null in OnHostClientSpawn.
This ensures hooks are only forced during deserialization when AOI is actually hiding objects.

In regular host mode without AOI, hooks fire normally via setters when values change.
This fixes the host mode unit tests while maintaining the AOI fix for the original issue.

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

* perf: optimize GeneratedSyncVarDeserialize methods to skip work when no hook

Check OnChanged != null before calculating changed and hostInitialSpawnInHostMode booleans.
No point doing that work if there's no hook to call.

Applied to all 4 GeneratedSyncVarDeserialize methods:
- GeneratedSyncVarDeserialize&lt;T&gt;
- GeneratedSyncVarDeserialize_GameObject
- GeneratedSyncVarDeserialize_NetworkIdentity
- GeneratedSyncVarDeserialize_NetworkBehaviour&lt;T&gt;

Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;

---------

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Co-authored-by: MrGadget1024 &lt;9826063+MrGadget1024@users.noreply.github.com&gt;
diff --git a/Assets/Mirror/Core/NetworkBehaviour.cs b/Assets/Mirror/Core/NetworkBehaviour.cs
@@ -565,7 +565,9 @@ public void GeneratedSyncVarSetter<T>(T value, ref T field, ulong dirtyBit, Acti
                     // in client-only mode, OnDeserialize would call it.
                     // we use hook guard to protect against deadlock where hook
                     // changes syncvar, calling hook again.
-                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit))
+                    // IMPORTANT: only call hook if object is visible to host client (in NetworkClient.spawned).
+                    // This prevents hooks from firing at spawn for objects out of AOI range.
+                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit) && NetworkClient.spawned.ContainsKey(netIdentity.netId))
                     {
                         SetSyncVarHookGuard(dirtyBit, true);
                         OnChanged(oldValue, value);
@@ -592,7 +594,9 @@ public void GeneratedSyncVarSetter_GameObject(GameObject value, ref GameObject f
                     // in client-only mode, OnDeserialize would call it.
                     // we use hook guard to protect against deadlock where hook
                     // changes syncvar, calling hook again.
-                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit))
+                    // IMPORTANT: only call hook if object is visible to host client (in NetworkClient.spawned).
+                    // This prevents hooks from firing at spawn for objects out of AOI range.
+                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit) && NetworkClient.spawned.ContainsKey(netIdentity.netId))
                     {
                         SetSyncVarHookGuard(dirtyBit, true);
                         OnChanged(oldValue, value);
@@ -619,7 +623,9 @@ public void GeneratedSyncVarSetter_NetworkIdentity(NetworkIdentity value, ref Ne
                     // in client-only mode, OnDeserialize would call it.
                     // we use hook guard to protect against deadlock where hook
                     // changes syncvar, calling hook again.
-                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit))
+                    // IMPORTANT: only call hook if object is visible to host client (in NetworkClient.spawned).
+                    // This prevents hooks from firing at spawn for objects out of AOI range.
+                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit) && NetworkClient.spawned.ContainsKey(netIdentity.netId))
                     {
                         SetSyncVarHookGuard(dirtyBit, true);
                         OnChanged(oldValue, value);
@@ -647,7 +653,9 @@ public void GeneratedSyncVarSetter_NetworkBehaviour<T>(T value, ref T field, ulo
                     // in client-only mode, OnDeserialize would call it.
                     // we use hook guard to protect against deadlock where hook
                     // changes syncvar, calling hook again.
-                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit))
+                    // IMPORTANT: only call hook if object is visible to host client (in NetworkClient.spawned).
+                    // This prevents hooks from firing at spawn for objects out of AOI range.
+                    if (NetworkServer.activeHost && !GetSyncVarHookGuard(dirtyBit) && NetworkClient.spawned.ContainsKey(netIdentity.netId))
                     {
                         SetSyncVarHookGuard(dirtyBit, true);
                         OnChanged(oldValue, value);
@@ -795,9 +803,14 @@ public void GeneratedSyncVarDeserialize<T>(ref T field, Action<T, T> OnChanged,
             field = value;
 
             // any hook? then call if changed.
-            if (OnChanged != null && !SyncVarEqual(previous, ref field))
+            // in host mode initial spawn, also call hook even if value hasn't changed,
+            // because the field was already set on server but hook wasn't called yet.
+            if (OnChanged != null)
             {
-                OnChanged(previous, field);
+                bool changed = !SyncVarEqual(previous, ref field);
+                bool hostInitialSpawnInHostMode = NetworkServer.activeHost && netIdentity.hostInitialSpawn;
+                if (changed || hostInitialSpawnInHostMode)
+                    OnChanged(previous, field);
             }
         }
 
@@ -856,9 +869,14 @@ public void GeneratedSyncVarDeserialize_GameObject(ref GameObject field, Action<
             field = GetSyncVarGameObject(netIdField, ref field);
 
             // any hook? then call if changed.
-            if (OnChanged != null && !SyncVarEqual(previousNetId, ref netIdField))
+            // in host mode initial spawn, also call hook even if value hasn't changed,
+            // because the field was already set on server but hook wasn't called yet.
+            if (OnChanged != null)
             {
-                OnChanged(previousGameObject, field);
+                bool changed = !SyncVarEqual(previousNetId, ref netIdField);
+                bool hostInitialSpawnInHostMode = NetworkServer.activeHost && netIdentity.hostInitialSpawn;
+                if (changed || hostInitialSpawnInHostMode)
+                    OnChanged(previousGameObject, field);
             }
         }
 
@@ -918,9 +936,14 @@ public void GeneratedSyncVarDeserialize_NetworkIdentity(ref NetworkIdentity fiel
             field = GetSyncVarNetworkIdentity(netIdField, ref field);
 
             // any hook? then call if changed.
-            if (OnChanged != null && !SyncVarEqual(previousNetId, ref netIdField))
+            // in host mode initial spawn, also call hook even if value hasn't changed,
+            // because the field was already set on server but hook wasn't called yet.
+            if (OnChanged != null)
             {
-                OnChanged(previousIdentity, field);
+                bool changed = !SyncVarEqual(previousNetId, ref netIdField);
+                bool hostInitialSpawnInHostMode = NetworkServer.activeHost && netIdentity.hostInitialSpawn;
+                if (changed || hostInitialSpawnInHostMode)
+                    OnChanged(previousIdentity, field);
             }
         }
 
@@ -982,9 +1005,14 @@ public void GeneratedSyncVarDeserialize_NetworkBehaviour<T>(ref T field, Action<
             field = GetSyncVarNetworkBehaviour(netIdField, ref field);
 
             // any hook? then call if changed.
-            if (OnChanged != null && !SyncVarEqual(previousNetId, ref netIdField))
+            // in host mode initial spawn, also call hook even if value hasn't changed,
+            // because the field was already set on server but hook wasn't called yet.
+            if (OnChanged != null)
             {
-                OnChanged(previousBehaviour, field);
+                bool changed = !SyncVarEqual(previousNetId, ref netIdField);
+                bool hostInitialSpawnInHostMode = NetworkServer.activeHost && netIdentity.hostInitialSpawn;
+                if (changed || hostInitialSpawnInHostMode)
+                    OnChanged(previousBehaviour, field);
             }
         }
 
diff --git a/Assets/Mirror/Core/NetworkClient.cs b/Assets/Mirror/Core/NetworkClient.cs
@@ -1384,7 +1384,31 @@ internal static void OnHostClientSpawn(SpawnMessage message)
                     aoi.SetHostVisibility(identity, true);
 
                 identity.isOwned = message.isOwner;
-                BootstrapIdentity(identity);
+
+                // Set flag to indicate initial spawn deserialization in host mode WITH AOI.
+                // This forces SyncVar hooks to fire even if values haven't changed,
+                // because the field was already set on server but hook wasn't called yet (object was out of range).
+                // Only set this flag when AOI is active, otherwise hooks should fire normally via setters.
+                identity.hostInitialSpawn = aoi != null;
+
+                // Configure flags before deserializing
+                InitializeIdentityFlags(identity);
+
+                // Deserialize components if any payload.
+                // This will trigger SyncVar hooks via GeneratedSyncVarDeserialize.
+                if (message.payload.Count > 0)
+                {
+                    using (NetworkReaderPooled payloadReader = NetworkReaderPool.Get(message.payload))
+                    {
+                        identity.DeserializeClient(payloadReader, true);
+                    }
+                }
+
+                // Clear flag after deserialization
+                identity.hostInitialSpawn = false;
+
+                // Invoke callbacks after deserializing
+                InvokeIdentityCallbacks(identity);
             }
         }
 
diff --git a/Assets/Mirror/Core/NetworkIdentity.cs b/Assets/Mirror/Core/NetworkIdentity.cs
@@ -118,6 +118,11 @@ public sealed class NetworkIdentity : MonoBehaviour
         // internal so NetworkManager can reset it from StopClient.
         internal bool clientStarted;
 
+        // flag to indicate we're deserializing initial spawn in host mode.
+        // used to force SyncVar hooks to fire even if value hasn't changed.
+        // only set temporarily during OnHostClientSpawn deserialization.
+        internal bool hostInitialSpawn;
+
         /// <summary>The set of network connections (players) that can see this object.</summary>
         public readonly Dictionary<int, NetworkConnectionToClient> observers =
             new Dictionary<int, NetworkConnectionToClient>();
