From fe8bd60fe7b27283c696a5b746414187695174b0 Mon Sep 17 00:00:00 2001
From: Jedediah Smith <jedediah@silencegreys.com>
Date: Wed, 2 Mar 2016 23:13:07 -0600
Subject: [PATCH] Send absolute position the first time an entity is seen


diff --git a/src/main/java/net/minecraft/server/EntityTrackerEntry.java b/src/main/java/net/minecraft/server/EntityTrackerEntry.java
index dd6c84b4a2..de0cf6b735 100644
--- a/src/main/java/net/minecraft/server/EntityTrackerEntry.java
+++ b/src/main/java/net/minecraft/server/EntityTrackerEntry.java
@@ -41,7 +41,19 @@ public class EntityTrackerEntry {
     private boolean x;
     private boolean y;
     public boolean b;
-    public final Set<EntityPlayer> trackedPlayers = Sets.newHashSet();
+    // Paper start
+    // Replace trackedPlayers Set with a Map. The value is true until the player receives
+    // their first update (which is forced to have absolute coordinates), false afterward.
+    public java.util.Map<EntityPlayer, Boolean> trackedPlayerMap = new java.util.HashMap<EntityPlayer, Boolean>();
+    public Set<EntityPlayer> trackedPlayers = trackedPlayerMap.keySet();
+
+    /**
+     * Requested in https://github.com/PaperMC/Paper/issues/1537 to allow intercepting packets
+     */
+    public void sendPlayerPacket(EntityPlayer player, Packet packet) {
+        player.playerConnection.sendPacket(packet);
+    }
+    // Paper end
 
     public EntityTrackerEntry(Entity entity, int i, int j, int k, boolean flag) {
         this.tracker = entity;
@@ -142,6 +154,7 @@ public class EntityTrackerEntry {
                 boolean flag1 = l1 * l1 + i2 * i2 + j2 * j2 >= 128L || this.a % 60 == 0;
                 boolean flag2 = Math.abs(j1 - this.yRot) >= 1 || Math.abs(k1 - this.xRot) >= 1;
 
+                if (this.a > 0 || this.tracker instanceof EntityArrow) { // Paper - Moved up
                 // CraftBukkit start - Code moved from below
                 if (flag1) {
                     this.xLoc = k;
@@ -155,7 +168,6 @@ public class EntityTrackerEntry {
                 }
                 // CraftBukkit end
 
-                if (this.a > 0 || this.tracker instanceof EntityArrow) {
                     if (l1 >= -32768L && l1 < 32768L && i2 >= -32768L && i2 < 32768L && j2 >= -32768L && j2 < 32768L && this.v <= 400 && !this.x && this.y == this.tracker.onGround) {
                         if ((!flag1 || !flag2) && !(this.tracker instanceof EntityArrow)) {
                             if (flag1) {
@@ -201,7 +213,26 @@ public class EntityTrackerEntry {
                 }
 
                 if (packet1 != null) {
-                    this.broadcast((Packet) packet1);
+                    // Paper start - ensure fresh viewers get an absolute position on their first update,
+                    // since we can't be certain what position they received in the spawn packet.
+                    if (packet1 instanceof PacketPlayOutEntityTeleport) {
+                        this.broadcast((Packet) packet1);
+                    } else {
+                        PacketPlayOutEntityTeleport teleportPacket = null;
+
+                        for (java.util.Map.Entry<EntityPlayer, Boolean> viewer : trackedPlayerMap.entrySet()) {
+                            if (viewer.getValue()) {
+                                viewer.setValue(false);
+                                if (teleportPacket == null) {
+                                    teleportPacket = new PacketPlayOutEntityTeleport(this.tracker);
+                                }
+                                sendPlayerPacket(viewer.getKey(), teleportPacket);
+                            } else {
+                                sendPlayerPacket(viewer.getKey(), (Packet) packet1);
+                            }
+                        }
+                    }
+                    // Paper end
                 }
 
                 this.d();
@@ -338,7 +369,7 @@ public class EntityTrackerEntry {
 
                     entityplayer.removeQueue.remove(Integer.valueOf(this.tracker.getId()));
                     // CraftBukkit end
-                    this.trackedPlayers.add(entityplayer);
+                    this.trackedPlayerMap.put(entityplayer, true); // Paper
                     Packet<?> packet = this.e();
 
                     entityplayer.playerConnection.sendPacket(packet);
-- 
2.21.0