From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Martijn Muijsers <martijnmuijsers@live.nl>
Date: Tue, 15 Aug 2023 21:04:55 +0200
Subject: [PATCH] Do crystal-portal proximity check before entity lookup

This adds a very cheap distance check when an end crystal is placed.

Attempting to respawn the dragon, which involves looking up the end crystal
entities near the portal, every time an end crystal is placed, can be slow on
some servers that have players placing end crystals as a style of combat.

The very cheap distance check prevents running the entity lookup every time.

diff --git a/src/main/java/net/minecraft/world/item/EndCrystalItem.java b/src/main/java/net/minecraft/world/item/EndCrystalItem.java
index ca1edc083847b47bb450b291723aca778a5912dc..e1696f6b77df4c8fceaece64701d4db78b0a4c42 100644
--- a/src/main/java/net/minecraft/world/item/EndCrystalItem.java
+++ b/src/main/java/net/minecraft/world/item/EndCrystalItem.java
@@ -29,7 +29,7 @@ public class EndCrystalItem extends Item {
         if (!iblockdata.is(Blocks.OBSIDIAN) && !iblockdata.is(Blocks.BEDROCK)) {
             return InteractionResult.FAIL;
         } else {
-            BlockPos blockposition1 = blockposition.above();
+            BlockPos blockposition1 = blockposition.above(); final BlockPos aboveBlockPosition = blockposition1; // Paper - OBFHELPER
 
             if (!world.isEmptyBlock(blockposition1)) {
                 return InteractionResult.FAIL;
@@ -56,7 +56,7 @@ public class EndCrystalItem extends Item {
                         EndDragonFight enderdragonbattle = ((ServerLevel) world).getDragonFight();
 
                         if (enderdragonbattle != null) {
-                            enderdragonbattle.tryRespawn();
+                            enderdragonbattle.tryRespawn(aboveBlockPosition); // Paper - Perf: Do crystal-portal proximity check before entity lookup
                         }
                     }
 
diff --git a/src/main/java/net/minecraft/world/level/dimension/end/EndDragonFight.java b/src/main/java/net/minecraft/world/level/dimension/end/EndDragonFight.java
index b9c85289776971f90eb5749262a9014befe465f7..d4f903c402765c6e8e1db99e148613748f530726 100644
--- a/src/main/java/net/minecraft/world/level/dimension/end/EndDragonFight.java
+++ b/src/main/java/net/minecraft/world/level/dimension/end/EndDragonFight.java
@@ -558,6 +558,12 @@ public class EndDragonFight {
     }
 
     public boolean tryRespawn() { // CraftBukkit - return boolean
+        // Paper start - Perf: Do crystal-portal proximity check before entity lookup
+        return this.tryRespawn(null);
+    }
+
+    public boolean tryRespawn(@Nullable BlockPos placedEndCrystalPos) { // placedEndCrystalPos is null if the tryRespawn() call was not caused by a placed end crystal
+        // Paper end - Perf: Do crystal-portal proximity check before entity lookup
         if (this.dragonKilled && this.respawnStage == null) {
             BlockPos blockposition = this.portalLocation;
 
@@ -575,6 +581,22 @@ public class EndDragonFight {
                 blockposition = this.portalLocation;
             }
 
+            // Paper start - Perf: Do crystal-portal proximity check before entity lookup
+            if (placedEndCrystalPos != null) {
+                // The end crystal must be 0 or 1 higher than the portal origin
+                int dy = placedEndCrystalPos.getY() - blockposition.getY();
+                if (dy != 0 && dy != 1) {
+                    return false;
+                }
+                // The end crystal must be within a distance of 1 in one planar direction, and 3 in the other
+                int dx = placedEndCrystalPos.getX() - blockposition.getX();
+                int dz = placedEndCrystalPos.getZ() - blockposition.getZ();
+                if (!((dx >= -1 && dx <= 1 && dz >= -3 && dz <= 3) || (dx >= -3 && dx <= 3 && dz >= -1 && dz <= 1))) {
+                    return false;
+                }
+            }
+            // Paper end - Perf: Do crystal-portal proximity check before entity lookup
+
             List<EndCrystal> list = Lists.newArrayList();
             BlockPos blockposition1 = blockposition.above(1);
             Iterator iterator = Direction.Plane.HORIZONTAL.iterator();