From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: kickash32 <kickash32@gmail.com>
Date: Mon, 19 Aug 2019 01:27:58 +0500
Subject: [PATCH] implement optional per player mob spawns


diff --git a/src/main/java/co/aikar/timings/WorldTimingsHandler.java b/src/main/java/co/aikar/timings/WorldTimingsHandler.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/co/aikar/timings/WorldTimingsHandler.java
+++ b/src/main/java/co/aikar/timings/WorldTimingsHandler.java
@@ -0,0 +0,0 @@ public class WorldTimingsHandler {
 
 
     public final Timing miscMobSpawning;
+    public final Timing playerMobDistanceMapUpdate;
 
     public final Timing poiUnload;
     public final Timing chunkUnload;
@@ -0,0 +0,0 @@ public class WorldTimingsHandler {
 
 
         miscMobSpawning = Timings.ofSafe(name + "Mob spawning - Misc");
+        playerMobDistanceMapUpdate = Timings.ofSafe(name + "Per Player Mob Spawning - Distance Map Update");
 
         poiUnload = Timings.ofSafe(name + "Chunk unload - POI");
         chunkUnload = Timings.ofSafe(name + "Chunk unload - Chunk");
diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -0,0 +0,0 @@ public class PaperWorldConfig {
             Bukkit.getLogger().warning("You have enabled permission-based Anti-Xray checking - depending on your permission plugin, this may cause performance issues");
         }
     }
+
+    public boolean perPlayerMobSpawns = false;
+    private void perPlayerMobSpawns() {
+        perPlayerMobSpawns = getBoolean("per-player-mob-spawns", false);
+    }
 }
 
diff --git a/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java b/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java
new file mode 100644
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java
@@ -0,0 +0,0 @@
+package com.destroystokyo.paper.util;
+
+import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectLinkedOpenHashSet;
+import java.util.List;
+import java.util.Map;
+import net.minecraft.core.SectionPos;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.ChunkPos;
+import org.spigotmc.AsyncCatcher;
+import java.util.HashMap;
+
+/** @author Spottedleaf */
+public final class PlayerMobDistanceMap {
+
+    private static final PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> EMPTY_SET = new PooledHashSets.PooledObjectLinkedOpenHashSet<>();
+
+    private final Map<ServerPlayer, SectionPos> players = new HashMap<>();
+    // we use linked for better iteration.
+    private final Long2ObjectOpenHashMap<PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer>> playerMap = new Long2ObjectOpenHashMap<>(32, 0.5f);
+    private int viewDistance;
+
+    private final PooledHashSets<ServerPlayer> pooledHashSets = new PooledHashSets<>();
+
+    public PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> getPlayersInRange(final ChunkPos chunkPos) {
+        return this.getPlayersInRange(chunkPos.x, chunkPos.z);
+    }
+
+    public PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> getPlayersInRange(final int chunkX, final int chunkZ) {
+        return this.playerMap.getOrDefault(ChunkPos.asLong(chunkX, chunkZ), EMPTY_SET);
+    }
+
+    public void update(final List<ServerPlayer> currentPlayers, final int newViewDistance) {
+        AsyncCatcher.catchOp("Distance map update");
+        final ObjectLinkedOpenHashSet<ServerPlayer> gone = new ObjectLinkedOpenHashSet<>(this.players.keySet());
+
+        final int oldViewDistance = this.viewDistance;
+        this.viewDistance = newViewDistance;
+
+        for (final ServerPlayer player : currentPlayers) {
+            if (player.isSpectator() || !player.affectsSpawning) {
+                continue; // will be left in 'gone' (or not added at all)
+            }
+
+            gone.remove(player);
+
+            final SectionPos newPosition = player.getLastSectionPos();
+            final SectionPos oldPosition = this.players.put(player, newPosition);
+
+            if (oldPosition == null) {
+                this.addNewPlayer(player, newPosition, newViewDistance);
+            } else {
+                this.updatePlayer(player, oldPosition, newPosition, oldViewDistance, newViewDistance);
+            }
+            //this.validatePlayer(player, newViewDistance); // debug only
+        }
+
+        for (final ServerPlayer player : gone) {
+            final SectionPos oldPosition = this.players.remove(player);
+            if (oldPosition != null) {
+                this.removePlayer(player, oldPosition, oldViewDistance);
+            }
+        }
+    }
+
+    // expensive op, only for debug
+    private void validatePlayer(final ServerPlayer player, final int viewDistance) {
+        int entiesGot = 0;
+        int expectedEntries = (2 * viewDistance + 1);
+        expectedEntries *= expectedEntries;
+
+        final SectionPos currPosition = player.getLastSectionPos();
+
+        final int centerX = currPosition.getX();
+        final int centerZ = currPosition.getZ();
+
+        for (final Long2ObjectLinkedOpenHashMap.Entry<PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer>> entry : this.playerMap.long2ObjectEntrySet()) {
+            final long key = entry.getLongKey();
+            final PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> map = entry.getValue();
+
+            if (map.referenceCount == 0) {
+                throw new IllegalStateException("Invalid map");
+            }
+
+            if (map.set.contains(player)) {
+                ++entiesGot;
+
+                final int chunkX = ChunkPos.getX(key);
+                final int chunkZ = ChunkPos.getZ(key);
+
+                final int dist = Math.max(Math.abs(chunkX - centerX), Math.abs(chunkZ - centerZ));
+
+                if (dist > viewDistance) {
+                    throw new IllegalStateException("Expected view distance " + viewDistance + ", got " + dist);
+                }
+            }
+        }
+
+        if (entiesGot != expectedEntries) {
+            throw new IllegalStateException("Expected " + expectedEntries + ", got " + entiesGot);
+        }
+    }
+
+    private void addPlayerTo(final ServerPlayer player, final int chunkX, final int chunkZ) {
+       this.playerMap.compute(ChunkPos.asLong(chunkX, chunkZ), (final Long key, final PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> players) -> {
+           if (players == null) {
+               return player.cachedSingleMobDistanceMap;
+           } else {
+               return PlayerMobDistanceMap.this.pooledHashSets.findMapWith(players, player);
+           }
+        });
+    }
+
+    private void removePlayerFrom(final ServerPlayer player, final int chunkX, final int chunkZ) {
+        this.playerMap.compute(ChunkPos.asLong(chunkX, chunkZ), (final Long keyInMap, final PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> players) -> {
+            return PlayerMobDistanceMap.this.pooledHashSets.findMapWithout(players, player); // rets null instead of an empty map
+        });
+    }
+
+    private void updatePlayer(final ServerPlayer player, final SectionPos oldPosition, final SectionPos newPosition, final int oldViewDistance, final int newViewDistance) {
+        final int toX = newPosition.getX();
+        final int toZ = newPosition.getZ();
+        final int fromX = oldPosition.getX();
+        final int fromZ = oldPosition.getZ();
+
+        final int dx = toX - fromX;
+        final int dz = toZ - fromZ;
+
+        final int totalX = Math.abs(fromX - toX);
+        final int totalZ = Math.abs(fromZ - toZ);
+
+        if (Math.max(totalX, totalZ) > (2 * oldViewDistance)) {
+            // teleported?
+            this.removePlayer(player, oldPosition, oldViewDistance);
+            this.addNewPlayer(player, newPosition, newViewDistance);
+            return;
+        }
+
+        // x axis is width
+        // z axis is height
+        // right refers to the x axis of where we moved
+        // top refers to the z axis of where we moved
+
+        if (oldViewDistance == newViewDistance) {
+            // same view distance
+
+            // used for relative positioning
+            final int up = 1 | (dz >> (Integer.SIZE - 1)); // 1 if dz >= 0, -1 otherwise
+            final int right = 1 | (dx >> (Integer.SIZE - 1)); // 1 if dx >= 0, -1 otherwise
+
+            // The area excluded by overlapping the two view distance squares creates four rectangles:
+            // Two on the left, and two on the right. The ones on the left we consider the "removed" section
+            // and on the right the "added" section.
+            // https://i.imgur.com/MrnOBgI.png is a reference image. Note that the outside border is not actually
+            // exclusive to the regions they surround.
+
+            // 4 points of the rectangle
+            int maxX; // exclusive
+            int minX; // inclusive
+            int maxZ; // exclusive
+            int minZ; // inclusive
+
+            if (dx != 0) {
+                // handle right addition
+
+                maxX = toX + (oldViewDistance * right) + right; // exclusive
+                minX = fromX + (oldViewDistance * right) + right; // inclusive
+                maxZ = fromZ + (oldViewDistance * up) + up; // exclusive
+                minZ = toZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.addPlayerTo(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dz != 0) {
+                // handle up addition
+
+                maxX = toX + (oldViewDistance * right) + right; // exclusive
+                minX = toX - (oldViewDistance * right); // inclusive
+                maxZ = toZ + (oldViewDistance * up) + up; // exclusive
+                minZ = fromZ + (oldViewDistance * up) + up; // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.addPlayerTo(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dx != 0) {
+                // handle left removal
+
+                maxX = toX - (oldViewDistance * right); // exclusive
+                minX = fromX - (oldViewDistance * right); // inclusive
+                maxZ = fromZ + (oldViewDistance * up) + up; // exclusive
+                minZ = toZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.removePlayerFrom(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dz != 0) {
+                // handle down removal
+
+                maxX = fromX + (oldViewDistance * right) + right; // exclusive
+                minX = fromX - (oldViewDistance * right); // inclusive
+                maxZ = toZ - (oldViewDistance * up); // exclusive
+                minZ = fromZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.removePlayerFrom(player, currX, currZ);
+                    }
+                }
+            }
+        } else {
+            // different view distance
+            // for now :)
+            this.removePlayer(player, oldPosition, oldViewDistance);
+            this.addNewPlayer(player, newPosition, newViewDistance);
+        }
+    }
+
+    private void removePlayer(final ServerPlayer player, final SectionPos position, final int viewDistance) {
+        final int x = position.getX();
+        final int z = position.getZ();
+
+        for (int xoff = -viewDistance; xoff <= viewDistance; ++xoff) {
+            for (int zoff = -viewDistance; zoff <= viewDistance; ++zoff) {
+                this.removePlayerFrom(player, x + xoff, z + zoff);
+            }
+        }
+    }
+
+    private void addNewPlayer(final ServerPlayer player, final SectionPos position, final int viewDistance) {
+        final int x = position.getX();
+        final int z = position.getZ();
+
+        for (int xoff = -viewDistance; xoff <= viewDistance; ++xoff) {
+            for (int zoff = -viewDistance; zoff <= viewDistance; ++zoff) {
+                this.addPlayerTo(player, x + xoff, z + zoff);
+            }
+        }
+    }
+}
diff --git a/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java b/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java
new file mode 100644
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java
@@ -0,0 +0,0 @@
+package com.destroystokyo.paper.util;
+
+import it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectLinkedOpenHashSet;
+import java.lang.ref.WeakReference;
+import java.util.Iterator;
+
+/** @author Spottedleaf */
+public class PooledHashSets<E> {
+
+    // we really want to avoid that equals() check as much as possible...
+    protected final Object2ObjectOpenHashMap<PooledObjectLinkedOpenHashSet<E>, PooledObjectLinkedOpenHashSet<E>> mapPool = new Object2ObjectOpenHashMap<>(64, 0.25f);
+
+    protected void decrementReferenceCount(final PooledObjectLinkedOpenHashSet<E> current) {
+        if (current.referenceCount == 0) {
+            throw new IllegalStateException("Cannot decrement reference count for " + current);
+        }
+        if (current.referenceCount == -1 || --current.referenceCount > 0) {
+            return;
+        }
+
+        this.mapPool.remove(current);
+        return;
+    }
+
+    public PooledObjectLinkedOpenHashSet<E> findMapWith(final PooledObjectLinkedOpenHashSet<E> current, final E object) {
+        final PooledObjectLinkedOpenHashSet<E> cached = current.getAddCache(object);
+
+        if (cached != null) {
+            if (cached.referenceCount != -1) {
+                ++cached.referenceCount;
+            }
+
+            decrementReferenceCount(current);
+
+            return cached;
+        }
+
+        if (!current.add(object)) {
+            return current;
+        }
+
+        // we use get/put since we use a different key on put
+        PooledObjectLinkedOpenHashSet<E> ret = this.mapPool.get(current);
+
+        if (ret == null) {
+            ret = new PooledObjectLinkedOpenHashSet<>(current);
+            current.remove(object);
+            this.mapPool.put(ret, ret);
+            ret.referenceCount = 1;
+        } else {
+            if (ret.referenceCount != -1) {
+                ++ret.referenceCount;
+            }
+            current.remove(object);
+        }
+
+        current.updateAddCache(object, ret);
+
+        decrementReferenceCount(current);
+        return ret;
+    }
+
+    // rets null if current.size() == 1
+    public PooledObjectLinkedOpenHashSet<E> findMapWithout(final PooledObjectLinkedOpenHashSet<E> current, final E object) {
+        if (current.set.size() == 1) {
+            decrementReferenceCount(current);
+            return null;
+        }
+
+        final PooledObjectLinkedOpenHashSet<E> cached = current.getRemoveCache(object);
+
+        if (cached != null) {
+            if (cached.referenceCount != -1) {
+                ++cached.referenceCount;
+            }
+
+            decrementReferenceCount(current);
+
+            return cached;
+        }
+
+        if (!current.remove(object)) {
+            return current;
+        }
+
+        // we use get/put since we use a different key on put
+        PooledObjectLinkedOpenHashSet<E> ret = this.mapPool.get(current);
+
+        if (ret == null) {
+            ret = new PooledObjectLinkedOpenHashSet<>(current);
+            current.add(object);
+            this.mapPool.put(ret, ret);
+            ret.referenceCount = 1;
+        } else {
+            if (ret.referenceCount != -1) {
+                ++ret.referenceCount;
+            }
+            current.add(object);
+        }
+
+        current.updateRemoveCache(object, ret);
+
+        decrementReferenceCount(current);
+        return ret;
+    }
+
+    public static final class PooledObjectLinkedOpenHashSet<E> implements Iterable<E> {
+
+        private static final WeakReference NULL_REFERENCE = new WeakReference(null);
+
+        final ObjectLinkedOpenHashSet<E> set;
+        int referenceCount; // -1 if special
+        int hash; // optimize hashcode
+
+        // add cache
+        WeakReference<E> lastAddObject = NULL_REFERENCE;
+        WeakReference<PooledObjectLinkedOpenHashSet<E>> lastAddMap = NULL_REFERENCE;
+
+        // remove cache
+        WeakReference<E> lastRemoveObject = NULL_REFERENCE;
+        WeakReference<PooledObjectLinkedOpenHashSet<E>> lastRemoveMap = NULL_REFERENCE;
+
+        public PooledObjectLinkedOpenHashSet() {
+            this.set = new ObjectLinkedOpenHashSet<>(2, 0.6f);
+        }
+
+        public PooledObjectLinkedOpenHashSet(final E single) {
+            this();
+            this.referenceCount = -1;
+            this.add(single);
+        }
+
+        public PooledObjectLinkedOpenHashSet(final PooledObjectLinkedOpenHashSet<E> other) {
+            this.set = other.set.clone();
+            this.hash = other.hash;
+        }
+
+        // from https://github.com/Spottedleaf/ConcurrentUtil/blob/master/src/main/java/ca/spottedleaf/concurrentutil/util/IntegerUtil.java
+        // generated by https://github.com/skeeto/hash-prospector
+        static int hash0(int x) {
+            x *= 0x36935555;
+            x ^= x >>> 16;
+            return x;
+        }
+
+        public PooledObjectLinkedOpenHashSet<E> getAddCache(final E element) {
+            final E currentAdd = this.lastAddObject.get();
+
+            if (currentAdd == null || !(currentAdd == element || currentAdd.equals(element))) {
+                return null;
+            }
+
+            final PooledObjectLinkedOpenHashSet<E> map = this.lastAddMap.get();
+            if (map == null || map.referenceCount == 0) {
+                // we need to ret null if ref count is zero as calling code will assume the map is in use
+                return null;
+            }
+
+            return map;
+        }
+
+        public PooledObjectLinkedOpenHashSet<E> getRemoveCache(final E element) {
+            final E currentRemove = this.lastRemoveObject.get();
+
+            if (currentRemove == null || !(currentRemove == element || currentRemove.equals(element))) {
+                return null;
+            }
+
+            final PooledObjectLinkedOpenHashSet<E> map = this.lastRemoveMap.get();
+            if (map == null || map.referenceCount == 0) {
+                // we need to ret null if ref count is zero as calling code will assume the map is in use
+                return null;
+            }
+
+            return map;
+        }
+
+        public void updateAddCache(final E element, final PooledObjectLinkedOpenHashSet<E> map) {
+            this.lastAddObject = new WeakReference<>(element);
+            this.lastAddMap = new WeakReference<>(map);
+        }
+
+        public void updateRemoveCache(final E element, final PooledObjectLinkedOpenHashSet<E> map) {
+            this.lastRemoveObject = new WeakReference<>(element);
+            this.lastRemoveMap = new WeakReference<>(map);
+        }
+
+        boolean add(final E element) {
+            boolean added =  this.set.add(element);
+
+            if (added) {
+                this.hash += hash0(element.hashCode());
+            }
+
+            return added;
+        }
+
+        boolean remove(Object element) {
+            boolean removed = this.set.remove(element);
+
+            if (removed) {
+                this.hash -= hash0(element.hashCode());
+            }
+
+            return removed;
+        }
+
+        @Override
+        public Iterator<E> iterator() {
+            return this.set.iterator();
+        }
+
+        @Override
+        public int hashCode() {
+            return this.hash;
+        }
+
+        @Override
+        public boolean equals(final Object other) {
+            if (!(other instanceof PooledObjectLinkedOpenHashSet)) {
+                return false;
+            }
+            if (this.referenceCount == 0) {
+                return other == this;
+            } else {
+                if (other == this) {
+                    // Unfortunately we are never equal to our own instance while in use!
+                    return false;
+                }
+                return this.hash == ((PooledObjectLinkedOpenHashSet)other).hash && this.set.equals(((PooledObjectLinkedOpenHashSet)other).set);
+            }
+        }
+
+        @Override
+        public String toString() {
+            return "PooledHashSet: size: " + this.set.size() + ", reference count: " + this.referenceCount + ", hash: " +
+                this.hashCode() + ", identity: " + System.identityHashCode(this) + " map: " + this.set.toString();
+        }
+    }
+} 
diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     private final Long2ByteMap chunkTypeCache;
     private final Queue<Runnable> unloadQueue;
     int viewDistance;
+    public final com.destroystokyo.paper.util.PlayerMobDistanceMap playerMobDistanceMap; // Paper
 
     // CraftBukkit start - recursion-safe executor for Chunk loadCallback() and unloadCallback()
     public final CallbackExecutor callbackExecutor = new CallbackExecutor();
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         this.overworldDataStorage = persistentStateManagerFactory;
         this.poiManager = new PoiManager(new File(this.storageFolder, "poi"), dataFixer, dsync, world);
         this.setViewDistance(viewDistance);
+        this.playerMobDistanceMap = this.level.paperConfig.perPlayerMobSpawns ? new com.destroystokyo.paper.util.PlayerMobDistanceMap() : null; // Paper
         // Paper start - no-tick view distance
         this.setNoTickViewDistance(this.level.paperConfig.noTickViewDistance);
         this.playerViewDistanceTickMap = new com.destroystokyo.paper.util.misc.PlayerAreaMap(this.pooledLinkedPlayerHashSets,
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         // Paper end - no-tick view distance
     }
 
+    // Paper start
+    public void updatePlayerMobTypeMap(Entity entity) {
+        if (!this.level.paperConfig.perPlayerMobSpawns) {
+            return;
+        }
+        int chunkX = (int)Math.floor(entity.getX()) >> 4;
+        int chunkZ = (int)Math.floor(entity.getZ()) >> 4;
+        int index = entity.getType().getCategory().ordinal();
+
+        for (ServerPlayer player : this.playerMobDistanceMap.getPlayersInRange(chunkX, chunkZ)) {
+            ++player.mobCounts[index];
+        }
+    }
+
+    public int getMobCountNear(ServerPlayer entityPlayer, net.minecraft.world.entity.MobCategory enumCreatureType) {
+        return entityPlayer.mobCounts[enumCreatureType.ordinal()];
+    }
+    // Paper end
+
     private static double euclideanDistanceSquared(ChunkPos pos, Entity entity) {
         double d0 = (double) SectionPos.sectionToBlockCoord(pos.x, 8);
         double d1 = (double) SectionPos.sectionToBlockCoord(pos.z, 8);
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
             this.level.getProfiler().push("naturalSpawnCount");
             this.level.timings.countNaturalMobs.startTiming(); // Paper - timings
             int l = this.distanceManager.getNaturalSpawnChunkCount();
-            NaturalSpawner.SpawnState spawnercreature_d = NaturalSpawner.createState(l, this.level.getAllEntities(), this::getFullChunk);
+            // Paper start - per player mob spawning
+            NaturalSpawner.SpawnState spawnercreature_d; // moved down
+            if (this.chunkMap.playerMobDistanceMap != null) {
+                // update distance map
+                this.level.timings.playerMobDistanceMapUpdate.startTiming();
+                this.chunkMap.playerMobDistanceMap.update(this.level.players, this.chunkMap.viewDistance);
+                this.level.timings.playerMobDistanceMapUpdate.stopTiming();
+                // re-set mob counts
+                for (ServerPlayer player : this.level.players) {
+                    Arrays.fill(player.mobCounts, 0);
+                }
+                spawnercreature_d = NaturalSpawner.createState(l, this.level.getAllEntities(), this::getFullChunk, true);
+            } else {
+                spawnercreature_d = NaturalSpawner.createState(l, this.level.getAllEntities(), this::getFullChunk, false);
+            }
+            // Paper end
             this.level.timings.countNaturalMobs.stopTiming(); // Paper - timings
 
             this.lastSpawnState = spawnercreature_d;
diff --git a/src/main/java/net/minecraft/server/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
@@ -0,0 +0,0 @@ import net.minecraft.world.damagesource.DamageSource;
 import net.minecraft.world.damagesource.EntityDamageSource;
 import net.minecraft.world.effect.MobEffectInstance;
 import net.minecraft.world.effect.MobEffects;
-import net.minecraft.world.entity.Entity;
-import net.minecraft.world.entity.EntitySelector;
-import net.minecraft.world.entity.HumanoidArm;
-import net.minecraft.world.entity.LivingEntity;
-import net.minecraft.world.entity.Mob;
-import net.minecraft.world.entity.NeutralMob;
+import net.minecraft.world.entity.*;
 import net.minecraft.world.entity.animal.horse.AbstractHorse;
 import net.minecraft.world.entity.item.ItemEntity;
 import net.minecraft.world.entity.monster.Monster;
@@ -0,0 +0,0 @@ public class ServerPlayer extends Player {
     public boolean queueHealthUpdatePacket = false;
     public net.minecraft.network.protocol.game.ClientboundSetHealthPacket queuedHealthUpdatePacket;
     // Paper end
+    // Paper start - mob spawning rework
+    public static final int ENUMCREATURETYPE_TOTAL_ENUMS = MobCategory.values().length;
+    public final int[] mobCounts = new int[ENUMCREATURETYPE_TOTAL_ENUMS]; // Paper
+    public final com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> cachedSingleMobDistanceMap;
+    // Paper end
 
     // CraftBukkit start
     public String displayName;
@@ -0,0 +0,0 @@ public class ServerPlayer extends Player {
         this.adventure$displayName = net.kyori.adventure.text.Component.text(this.getScoreboardName()); // Paper
         this.bukkitPickUpLoot = true;
         this.maxHealthCache = this.getMaxHealth();
+        this.cachedSingleMobDistanceMap = new com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<>(this); // Paper
     }
 
     // Yes, this doesn't match Vanilla, but it's the best we can do for now.
diff --git a/src/main/java/net/minecraft/world/level/NaturalSpawner.java b/src/main/java/net/minecraft/world/level/NaturalSpawner.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/world/level/NaturalSpawner.java
+++ b/src/main/java/net/minecraft/world/level/NaturalSpawner.java
@@ -0,0 +0,0 @@ import net.minecraft.core.Registry;
 import net.minecraft.core.SectionPos;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.tags.BlockTags;
 import net.minecraft.tags.FluidTags;
 import net.minecraft.tags.Tag;
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
 
     private NaturalSpawner() {}
 
+    // Paper start - add countMobs parameter
     public static NaturalSpawner.SpawnState createState(int spawningChunkCount, Iterable<Entity> entities, NaturalSpawner.ChunkGetter chunkSource) {
+        return createState(spawningChunkCount, entities, chunkSource, false);
+    }
+    public static NaturalSpawner.SpawnState createState(int spawningChunkCount, Iterable<Entity> entities, NaturalSpawner.ChunkGetter chunkSource, boolean countMobs) {
+    // Paper end - add countMobs parameter
         PotentialCalculator spawnercreatureprobabilities = new PotentialCalculator();
         Object2IntOpenHashMap<MobCategory> object2intopenhashmap = new Object2IntOpenHashMap();
         Iterator iterator = entities.iterator();
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
                     }
 
                     object2intopenhashmap.addTo(enumcreaturetype, 1);
+                    // Paper start
+                    if (countMobs) {
+                        chunk.level.getChunkSource().chunkMap.updatePlayerMobTypeMap(entity);
+                    }
+                    // Paper end
                 });
             }
         }
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
                 continue;
             }
 
-            if ((spawnAnimals || !enumcreaturetype.isFriendly()) && (spawnMonsters || enumcreaturetype.isFriendly()) && (rareSpawn || !enumcreaturetype.isPersistent()) && info.a(enumcreaturetype, limit)) {
+            // Paper start - only allow spawns upto the limit per chunk and update count afterwards
+            int currEntityCount = info.mobCategoryCounts.getInt(enumcreaturetype);
+            int k1 = limit * info.getSpawnableChunkCount() / NaturalSpawner.MAGIC_NUMBER;
+            int difference = k1 - currEntityCount;
+
+            if (world.paperConfig.perPlayerMobSpawns) {
+                int minDiff = Integer.MAX_VALUE;
+                for (ServerPlayer entityplayer : world.getChunkSource().chunkMap.playerMobDistanceMap.getPlayersInRange(chunk.getPos())) {
+                    minDiff = Math.min(limit - world.getChunkSource().chunkMap.getMobCountNear(entityplayer, enumcreaturetype), minDiff);
+                }
+                difference = (minDiff == Integer.MAX_VALUE) ? 0 : minDiff;
+            }
+            // Paper end
+
+            // Paper start - per player mob spawning
+            if ((spawnAnimals || !enumcreaturetype.isFriendly()) && (spawnMonsters || enumcreaturetype.isFriendly()) && (spawnAnimals || !enumcreaturetype.isPersistent())  && info.a(enumcreaturetype, limit) && difference > 0) {
                 // CraftBukkit end
                 Objects.requireNonNull(info);
                 NaturalSpawner.SpawnPredicate spawnercreature_c = info::canSpawn;
 
                 Objects.requireNonNull(info);
-                NaturalSpawner.spawnCategoryForChunk(enumcreaturetype, world, chunk, spawnercreature_c, info::afterSpawn);
+                int spawnCount = NaturalSpawner.spawnCategoryForChunk(enumcreaturetype, world, chunk, spawnercreature_c, info::afterSpawn,
+                    difference, world.paperConfig.perPlayerMobSpawns ? world.getChunkSource().chunkMap::updatePlayerMobTypeMap : null);
+                info.mobCategoryCounts.mergeInt(enumcreaturetype, spawnCount, Integer::sum);
+                // Paper end - per player mob spawning
             }
         }
 
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
         world.getProfiler().pop();
     }
 
+    // Paper start - add parameters and int ret type
     public static void spawnCategoryForChunk(MobCategory group, ServerLevel world, LevelChunk chunk, NaturalSpawner.SpawnPredicate checker, NaturalSpawner.AfterSpawnCallback runner) {
+        spawnCategoryForChunk(group, world, chunk, checker, runner);
+    }
+    public static int spawnCategoryForChunk(MobCategory group, ServerLevel world, LevelChunk chunk, NaturalSpawner.SpawnPredicate checker, NaturalSpawner.AfterSpawnCallback runner, int maxSpawns, Consumer<Entity> trackEntity) {
+        // Paper end - add parameters and int ret type
         BlockPos blockposition = NaturalSpawner.getRandomPosWithin(world, chunk);
 
         if (blockposition.getY() >= world.getMinBuildHeight() + 1) {
-            NaturalSpawner.spawnCategoryForPosition(group, world, (ChunkAccess) chunk, blockposition, checker, runner);
+            return NaturalSpawner.spawnCategoryForPosition(group, world, (ChunkAccess) chunk, blockposition, checker, runner, maxSpawns, trackEntity); // Paper
         }
+        return 0; // Paper
     }
 
     @VisibleForDebug
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
         });
     }
 
+    // Paper start - add maxSpawns parameter and return spawned mobs
     public static void spawnCategoryForPosition(MobCategory group, ServerLevel world, ChunkAccess chunk, BlockPos pos, NaturalSpawner.SpawnPredicate checker, NaturalSpawner.AfterSpawnCallback runner) {
+        spawnCategoryForPosition(group, world,chunk, pos, checker, runner);
+    }
+    public static int spawnCategoryForPosition(MobCategory group, ServerLevel world, ChunkAccess chunk, BlockPos pos, NaturalSpawner.SpawnPredicate checker, NaturalSpawner.AfterSpawnCallback runner, int maxSpawns, Consumer<Entity> trackEntity) {
+    // Paper end - add maxSpawns parameter and return spawned mobs
         StructureFeatureManager structuremanager = world.structureFeatureManager();
         ChunkGenerator chunkgenerator = world.getChunkSource().getGenerator();
         int i = pos.getY();
         BlockState iblockdata = world.getTypeIfLoadedAndInBounds(pos); // Paper - don't load chunks for mob spawn
+        int j = 0; // Paper - moved up
 
         if (iblockdata != null && !iblockdata.isRedstoneConductor(chunk, pos)) { // Paper - don't load chunks for mob spawn
             BlockPos.MutableBlockPos blockposition_mutableblockposition = new BlockPos.MutableBlockPos();
-            int j = 0;
+            // Paper - moved up
             int k = 0;
 
             while (k < 3) {
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
                                     // Paper start
                                     Boolean doSpawning = isValidSpawnPostitionForType(world, group, structuremanager, chunkgenerator, biomesettingsmobs_c, blockposition_mutableblockposition, d2);
                                     if (doSpawning == null) {
-                                        return;
+                                        return j; // Paper
                                     }
                                     if (doSpawning && checker.test(biomesettingsmobs_c.type, blockposition_mutableblockposition, chunk)) {
                                         // Paper end
                                         Mob entityinsentient = NaturalSpawner.getMobForSpawn(world, biomesettingsmobs_c.type);
 
                                         if (entityinsentient == null) {
-                                            return;
+                                            return j; // Paper
                                         }
 
                                         entityinsentient.moveTo(d0, (double) i, d1, world.random.nextFloat() * 360.0F, 0.0F);
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
                                                 ++j;
                                                 ++k1;
                                                 runner.run(entityinsentient, chunk);
+                                                // Paper start
+                                                if (trackEntity != null) {
+                                                    trackEntity.accept(entityinsentient);
+                                                }
+                                                // Paper end
                                             }
                                             // CraftBukkit end
-                                            if (j >= entityinsentient.getMaxSpawnClusterSize()) {
-                                                return;
+                                            if (j >= entityinsentient.getMaxSpawnClusterSize() || j >= maxSpawns) { // Paper
+                                                return j; // Paper
                                             }
 
                                             if (entityinsentient.isMaxGroupSizeReached(k1)) {
@@ -0,0 +0,0 @@ public final class NaturalSpawner {
             }
 
         }
+        return j; // Paper
     }
 
     private static boolean isRightDistanceToPlayerAndSpawnPoint(ServerLevel world, ChunkAccess chunk, BlockPos.MutableBlockPos pos, double squaredDistance) {
