From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: MrPowerGamerBR <git@mrpowergamerbr.com>
Date: Thu, 23 Nov 2023 14:36:47 -0300
Subject: [PATCH] Optimize "canSee" checks

The "canSee" checks is in a hot path, invoked by each entity for each player on the server if they are in tracking range, so optimizing it is pretty nice

First, we change the original "HashMap" to fastutil's "Object2ObjectOpenHashMap", because the containsKey throughput is better

Then, we add a "isEmpty()" check before attempting to check if the map contains something

This seems stupid, but it does seem that it improves the performance a bit, and it makes sense, "containsKey(...)" does not attempt to check the map size before attempting to check if the map contains the key

We also create a "canSee" method tailored for "ChunkMap#updatePlayer()", a method without the equals check (the "updatePlayer()" already checks if the entity is the same entity) because the CraftPlayer's `equals()` check is a *bit* expensive compared to only checking the object's identity, and because the identity has already been check, we don't need to check it twice.

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 52a6a4badace15a983f0acb431036bd704d9cebd..7c19a4d11546bbcbf144feddee72733915bd3abd 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -1289,7 +1289,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 // Paper end - Configurable entity tracking range by Y
 
                 // CraftBukkit start - respect vanish API
-                if (flag && !player.getBukkitEntity().canSee(this.entity.getBukkitEntity())) { // Paper - only consider hits
+                if (flag && !player.getBukkitEntity().canSeeChunkMapUpdatePlayer(this.entity.getBukkitEntity())) { // Paper - only consider hits // SparklyPaper - optimize canSee checks
                     flag = false;
                 }
                 // CraftBukkit end
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
index 554714e449d1d2439b05d7e15f72afccd17d4df5..405a65b52f5b4cd9a9a19e3e6369d98c39f306bc 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
@@ -205,7 +205,7 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
     private boolean hasPlayedBefore = false;
     private final ConversationTracker conversationTracker = new ConversationTracker();
     private final Set<String> channels = new HashSet<String>();
-    private final Map<UUID, Set<WeakReference<Plugin>>> invertedVisibilityEntities = new HashMap<>();
+    private final Map<UUID, Set<WeakReference<Plugin>>> invertedVisibilityEntities = new it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap<>(); // SparklyPaper - optimize canSee checks
     private final Set<UUID> unlistedEntities = new HashSet<>(); // Paper - Add Listing API for Player
     private static final WeakHashMap<Plugin, WeakReference<Plugin>> pluginWeakReferences = new WeakHashMap<>();
     private int hash = 0;
@@ -2264,9 +2264,16 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
 
     @Override
     public boolean canSee(org.bukkit.entity.Entity entity) {
-        return this.equals(entity) || entity.isVisibleByDefault() ^ this.invertedVisibilityEntities.containsKey(entity.getUniqueId()); // SPIGOT-7312: Can always see self
+        return this.equals(entity) || entity.isVisibleByDefault() ^ (!invertedVisibilityEntities.isEmpty() && this.invertedVisibilityEntities.containsKey(entity.getUniqueId())); // SPIGOT-7312: Can always see self // SparklyPaper - optimize canSee checks
     }
 
+    // SparklyPaper - optimize canSee checks
+    // The check in ChunkMap#updatePlayer already rejects if it is the same entity, so we don't need to check it twice, especially because CraftPlayer's equals check is a bit expensive
+    public boolean canSeeChunkMapUpdatePlayer(org.bukkit.entity.Entity entity) {
+        return entity.isVisibleByDefault() ^ (!invertedVisibilityEntities.isEmpty() && this.invertedVisibilityEntities.containsKey(entity.getUniqueId())); // SPIGOT-7312: Can always see self // SparklyPaper - optimize canSee checks
+    }
+    // SparklyPaper end
+
     public boolean canSeePlayer(UUID uuid) {
         org.bukkit.entity.Entity entity = this.getServer().getPlayer(uuid);