From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Martijn Muijsers <martijnmuijsers@live.nl>
Date: Mon, 21 Aug 2023 21:05:09 +0200
Subject: [PATCH] Optimize nearest structure border iteration

Getting the nearest generated structure contains a nested set of loops that
iterates over all chunks at a specific chessboard distance. It does this by
iterating over the entire square of chunks within that distance, and checking
if the coordinates are at exactly the right distance to be on the border.

This patch optimizes the iteration by only iterating over the border chunks.
This evaluated chunks are the same, and in the same order, as before, to
ensure that the returned found structure (which may for example be a buried
treasure that will be marked on a treasure map) is the same as in vanilla.

diff --git a/src/main/java/net/minecraft/world/level/chunk/ChunkGenerator.java b/src/main/java/net/minecraft/world/level/chunk/ChunkGenerator.java
index e9239f90e59d1429fc7a2618e0fd3b8a57633b87..a21db714971025448dd915b2281a1d9121eaf758 100644
--- a/src/main/java/net/minecraft/world/level/chunk/ChunkGenerator.java
+++ b/src/main/java/net/minecraft/world/level/chunk/ChunkGenerator.java
@@ -260,12 +260,15 @@ public abstract class ChunkGenerator {
         int i1 = placement.spacing();
 
         for (int j1 = -radius; j1 <= radius; ++j1) {
-            boolean flag1 = j1 == -radius || j1 == radius;
+            // Paper start - Perf: iterate over border chunks instead of entire square chunk area
+            boolean flag1 = j1 == -radius || j1 == radius; final boolean onBorderAlongZAxis = flag1; // Paper - OBFHELPER
 
-            for (int k1 = -radius; k1 <= radius; ++k1) {
-                boolean flag2 = k1 == -radius || k1 == radius;
+            for (int k1 = -radius; k1 <= radius; k1 += onBorderAlongZAxis ? 1 : radius * 2) {
+                // boolean flag2 = k1 == -radius || k1 == radius;
 
-                if (flag1 || flag2) {
+                // if (flag1 || flag2) {
+                if (true) {
+                    // Paper end - Perf: iterate over border chunks instead of entire square chunk area
                     int l1 = centerChunkX + i1 * j1;
                     int i2 = centerChunkZ + i1 * k1;
                     ChunkPos chunkcoordintpair = placement.getPotentialStructureChunk(seed, l1, i2);