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) and we cache the "isVisibleByDefault()" result between runs (this also seems a bit overkill because "isVisibleByDefault()" is just a method that returns a boolean, but because this is a hotpath, we need all optimizations that we can get

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index caa73632aee15583c6b6ed12a668c8f49b794708..6fff96c1c0fc1442803718fa36ac30a35b6ae2d7 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -1326,6 +1326,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         private final int range;
         SectionPos lastSectionPos;
         public final Set<ServerPlayerConnection> seenBy = new it.unimi.dsi.fastutil.objects.ReferenceOpenHashSet<>(); // Paper - optimise map impl
+        boolean visibleByDefault; // SparklyPaper - optimize canSee checks
 
         public TrackedEntity(Entity entity, int i, int j, boolean flag) {
             this.serverEntity = new ServerEntity(ChunkMap.this.level, entity, j, flag, this::broadcast, this.seenBy); // CraftBukkit
@@ -1340,6 +1341,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         final void updatePlayers(com.destroystokyo.paper.util.misc.PooledLinkedHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> newTrackerCandidates) {
             com.destroystokyo.paper.util.misc.PooledLinkedHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> oldTrackerCandidates = this.lastTrackerCandidates;
             this.lastTrackerCandidates = newTrackerCandidates;
+            this.visibleByDefault = entity.visibleByDefault; // SparklyPaper - optimize canSee checks
 
             if (newTrackerCandidates != null) {
                 Object[] rawData = newTrackerCandidates.getBackingSet();
@@ -1436,7 +1438,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 // Paper end - check 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(), visibleByDefault)) { // 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 83aaf3e6e377d731ce02f779f80b7bf5db46f89f..3a02f92b57563b42680f4b867d681d2232c748cc 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
@@ -183,7 +183,7 @@ 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
     private static final WeakHashMap<Plugin, WeakReference<Plugin>> pluginWeakReferences = new WeakHashMap<>();
     private int hash = 0;
@@ -2070,9 +2070,16 @@ 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, boolean visibleByDefault) {
+        return visibleByDefault ^ (!invertedVisibilityEntities.isEmpty() && this.invertedVisibilityEntities.containsKey(entity.getUniqueId())); // SPIGOT-7312: Can always see self // SparklyPaper - optimize canSee checks
+    }
+    // SparklyPaper end
+
     public boolean canSee(UUID uuid) {
         org.bukkit.entity.Entity entity = this.getServer().getPlayer(uuid);
         if (entity == null) {