#1409: Add methods to get players seeing specific chunks

src/main/java/org/bukkit/craftbukkit/CraftChunk.java

@@ -48,6 +48,7 @@
 import org.bukkit.craftbukkit.block.CraftBlock;
 import org.bukkit.craftbukkit.block.data.CraftBlockData;
 import org.bukkit.entity.Entity;
+import org.bukkit.entity.Player;
 import org.bukkit.generator.structure.GeneratedStructure;
 import org.bukkit.generator.structure.Structure;
 import org.bukkit.persistence.PersistentDataContainer;
@@ -376,6 +377,11 @@ public Collection<GeneratedStructure> getStructures(Structure structure) {
         return getCraftWorld().getStructures(getX(), getZ(), structure);
     }
 
+    @Override
+    public Collection<Player> getPlayersSeeingChunk() {
+        return getWorld().getPlayersSeeingChunk(this);
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -350,6 +350,31 @@ public boolean refreshChunk(int x, int z) {
         return true;
     }
 
+    @Override
+    public Collection<Player> getPlayersSeeingChunk(Chunk chunk) {
+        Preconditions.checkArgument(chunk != null, "chunk cannot be null");
+
+        return getPlayersSeeingChunk(chunk.getX(), chunk.getZ());
+    }
+
+    @Override
+    public Collection<Player> getPlayersSeeingChunk(int x, int z) {
+        if (!isChunkLoaded(x, z)) {
+            return Collections.emptySet();
+        }
+
+        List<EntityPlayer> players = world.getChunkSource().chunkMap.getPlayers(new ChunkCoordIntPair(x, z), false);
+
+        if (players.isEmpty()) {
+            return Collections.emptySet();
+        }
+
+        return players.stream()
+                .filter(Objects::nonNull)
+                .map(EntityPlayer::getBukkitEntity)
+                .collect(Collectors.toUnmodifiableSet());
+    }
+
     @Override
     public boolean isChunkInUse(int x, int z) {
         return isChunkLoaded(x, z);