CHANGED TO MIRROR

Assets/Mirror/Components/InterestManagement/Distance/DistanceInterestManagement.cs

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+// straight forward Vector3.Distance based interest management.
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace Mirror
+{
+    public class DistanceInterestManagement : InterestManagement
+    {
+        [Tooltip("The maximum range that objects will be visible at. Add DistanceInterestManagementCustomRange onto NetworkIdentities for custom ranges.")]
+        public int visRange = 10;
+
+        [Tooltip("Rebuild all every 'rebuildInterval' seconds.")]
+        public float rebuildInterval = 1;
+        double lastRebuildTime;
+
+        // helper function to get vis range for a given object, or default.
+        int GetVisRange(NetworkIdentity identity)
+        {
+            DistanceInterestManagementCustomRange custom = identity.GetComponent<DistanceInterestManagementCustomRange>();
+            return custom != null ? custom.visRange : visRange;
+        }
+
+        public override bool OnCheckObserver(NetworkIdentity identity, NetworkConnection newObserver)
+        {
+            int range = GetVisRange(identity);
+            return Vector3.Distance(identity.transform.position, newObserver.identity.transform.position) < range;
+        }
+
+        public override void OnRebuildObservers(NetworkIdentity identity, HashSet<NetworkConnection> newObservers, bool initialize)
+        {
+            // cache range and .transform because both call GetComponent.
+            int range = GetVisRange(identity);
+            Vector3 position = identity.transform.position;
+
+            // brute force distance check
+            // -> only player connections can be observers, so it's enough if we
+            //    go through all connections instead of all spawned identities.
+            // -> compared to UNET's sphere cast checking, this one is orders of
+            //    magnitude faster. if we have 10k monsters and run a sphere
+            //    cast 10k times, we will see a noticeable lag even with physics
+            //    layers. but checking to every connection is fast.
+            foreach (NetworkConnectionToClient conn in NetworkServer.connections.Values)
+            {
+                // authenticated and joined world with a player?
+                if (conn != null && conn.isAuthenticated && conn.identity != null)
+                {
+                    // check distance
+                    if (Vector3.Distance(conn.identity.transform.position, position) < range)
+                    {
+                        newObservers.Add(conn);
+                    }
+                }
+            }
+        }
+
+        void Update()
+        {
+            // only on server
+            if (!NetworkServer.active) return;
+
+            // rebuild all spawned NetworkIdentity's observers every interval
+            if (NetworkTime.localTime >= lastRebuildTime + rebuildInterval)
+            {
+                RebuildAll();
+                lastRebuildTime = NetworkTime.localTime;
+            }
+        }
+    }
+}

Assets/Mirror/Components/InterestManagement/Distance/DistanceInterestManagement.cs.meta

@@ -0,0 +1,11 @@
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Assets/Mirror/Components/InterestManagement/Distance/DistanceInterestManagementCustomRange.cs

@@ -0,0 +1,14 @@
+// add this to NetworkIdentities for custom range if needed.
+// only works with DistanceInterestManagement.
+using UnityEngine;
+
+namespace Mirror
+{
+    [RequireComponent(typeof(NetworkIdentity))]
+    [DisallowMultipleComponent]
+    public class DistanceInterestManagementCustomRange : MonoBehaviour
+    {
+        [Tooltip("The maximum range that objects will be visible at.")]
+        public int visRange = 20;
+    }
+}

Assets/Mirror/Components/InterestManagement/Distance/DistanceInterestManagementCustomRange.cs.meta

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