perf: skip split-screen system-mate checks on dedicated server

The EntityTracker and TrackedEntity classes have O(players^2 * entities)
loops that check IsSameSystem() for split-screen couch co-op visibility
expansion. On the dedicated server, all players are remote so
IsSameSystem() always returns false, making these loops pure overhead.

Skip them entirely when g_Win64DedicatedServer is true. The original
split-screen logic is preserved for game client LAN hosting.

.gitignore

@@ -420,3 +420,4 @@ server-data/
 tools/*.class
 tools/*.swf
 tools/staging/
+tools/server-monitor/

Minecraft.Client/EntityTracker.cpp

@@ -21,6 +21,10 @@
 #include "..\Minecraft.World\net.minecraft.world.level.chunk.h"
 #include "PlayerConnection.h"
 
+#ifdef _WINDOWS64
+extern bool g_Win64DedicatedServer;
+#endif
+
 EntityTracker::EntityTracker(ServerLevel *level)
 {
     this->level = level;
@@ -139,32 +143,40 @@ void EntityTracker::tick()
 	// 4J Stu - If one player on a system is updated, then make sure they all are as they all have their
 	// range extended to include entities visible by any other player on the system
 	// Fix for #11194 - Gameplay: Host player and their split-screen avatars can become invisible and invulnerable to client.
-	MinecraftServer *server = MinecraftServer::getInstance();
+	// NOTE: On dedicated servers, IsSameSystem() always returns false for remote
-	for( unsigned int i = 0; i < server->getPlayers()->players.size(); i++ )
+	// players (no split-screen), so this loop does nothing. Skip it entirely to
+	// avoid the O(players * movedPlayers) overhead.
+#ifdef _WINDOWS64
+	if (!g_Win64DedicatedServer)
+#endif
 	{
-		shared_ptr<ServerPlayer> ep = server->getPlayers()->players[i];			
+		MinecraftServer *server = MinecraftServer::getInstance();
-		if( ep->dimension != level->dimension->id ) continue;
+		for( unsigned int i = 0; i < server->getPlayers()->players.size(); i++ )
-
-		if( ep->connection == nullptr ) continue;
-		INetworkPlayer *thisPlayer = ep->connection->getNetworkPlayer();
-		if( thisPlayer == nullptr ) continue;
-
-		bool addPlayer = false;
-		for (unsigned int j = 0; j < movedPlayers.size(); j++)
 		{
-			shared_ptr<ServerPlayer> sp = movedPlayers[j];
+			shared_ptr<ServerPlayer> ep = server->getPlayers()->players[i];
+			if( ep->dimension != level->dimension->id ) continue;
 
-			if( sp == ep ) break;
+			if( ep->connection == nullptr ) continue;
+			INetworkPlayer *thisPlayer = ep->connection->getNetworkPlayer();
+			if( thisPlayer == nullptr ) continue;
 
-			if(sp->connection == nullptr) continue;
+			bool addPlayer = false;
-			INetworkPlayer *otherPlayer = sp->connection->getNetworkPlayer();
+			for (unsigned int j = 0; j < movedPlayers.size(); j++)
-			if( otherPlayer != nullptr && thisPlayer->IsSameSystem(otherPlayer) )
 			{
-				addPlayer = true;
+				shared_ptr<ServerPlayer> sp = movedPlayers[j];
-				break;
+
+				if( sp == ep ) break;
+
+				if(sp->connection == nullptr) continue;
+				INetworkPlayer *otherPlayer = sp->connection->getNetworkPlayer();
+				if( otherPlayer != nullptr && thisPlayer->IsSameSystem(otherPlayer) )
+				{
+					addPlayer = true;
+					break;
+				}
 			}
-		}		
+			if( addPlayer ) movedPlayers.push_back( ep );
-		if( addPlayer ) movedPlayers.push_back( ep );
+		}
 	}
 
     for (unsigned int i = 0; i < movedPlayers.size(); i++)

Minecraft.Client/TrackedEntity.cpp

@@ -23,6 +23,10 @@
 
 #include <memory>
 
+#ifdef _WINDOWS64
+extern bool g_Win64DedicatedServer;
+#endif
+
 TrackedEntity::TrackedEntity(shared_ptr<Entity> e, int range, int updateInterval, bool trackDelta)
 {
 	// 4J added initialisers
@@ -351,6 +355,19 @@ void TrackedEntity::sendDirtyEntityData()
 
 void TrackedEntity::broadcast(shared_ptr<Packet> packet)
 {
+#ifdef _WINDOWS64
+	// On dedicated servers, IsSameSystem() always returns false for remote players
+	// (no split-screen), so the dedup loop never filters anything. Skip straight
+	// to sending to all players in seenBy to avoid O(seenBy^2) overhead.
+	if (g_Win64DedicatedServer)
+	{
+		for (auto& player : seenBy)
+		{
+			player->connection->send(packet);
+		}
+		return;
+	}
+#endif
 	if( Packet::canSendToAnyClient( packet ) )
 	{
 		// 4J-PB - due to the knockback on a player being hit, we need to send to all players, but limit the network traffic here to players that have not already had it sent to their system
@@ -462,7 +479,13 @@ TrackedEntity::eVisibility TrackedEntity::isVisible(EntityTracker *tracker, shar
 	// 4J - added. Try and find other players who are in the same dimension as this one and on the same machine, and extend our visibility
 	// so things are consider visible to this player if they are near the other one. This is because we only send entity tracking info to
 	// players who canReceiveAllPackets().
-	if(!bVisible)
+	// NOTE: On dedicated servers, all real players are remote so IsSameSystem()
+	// always returns false. Skip this O(players) loop entirely.
+#ifdef _WINDOWS64
+	if (!bVisible && !g_Win64DedicatedServer)
+#else
+	if (!bVisible)
+#endif
 	{
 		MinecraftServer *server = MinecraftServer::getInstance();
 		INetworkPlayer *thisPlayer = sp->connection->getNetworkPlayer();