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 273bb38f14b8af08d123e02742d365fb5d91cdf5..5f51e64cb0611a4ba6bdcdcacbcba1063a7f3a5c 100644
--- a/src/main/java/net/minecraft/world/item/EndCrystalItem.java
+++ b/src/main/java/net/minecraft/world/item/EndCrystalItem.java
@@ -30,7 +30,7 @@ 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;
@@ -58,7 +58,7 @@ 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 4a0479fcff94bf6a1f239c1f694202345cdea1d4..84300f2f7b7be4f5281edd8e263646dbcbb3ba07 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
@@ -560,6 +560,12 @@ 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;
 
@@ -577,6 +583,22 @@ 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();