From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Phoenix616 <mail@moep.tv>
Date: Mon, 13 Jan 2020 15:40:32 +0100
Subject: [PATCH] Seed based feature search

This tries to work around the issue where the server will load
surrounding chunks up to a radius of 100 chunks in order to search for
features e.g. when running the /locate command or for treasure maps
(issue #2312).
This is done by backporting Mojang's change in 1.17 which makes it so
that the biome (generated by the seed) is checked first if the feature
can be generated before actually to load the chunk.

Additionally to that the center location of the target chunk is simply
returned if the chunk is not loaded to avoid the sync chunk load.
As this can lead to less precise locations a toggle is provided to
enable the sync loading of the target chunk again.

The main downside of this is that it breaks once the seed or generator
changes but this should usually not happen. A config option to disable
this completely is added though in case that should ever be necessary.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 1f673932e329f7e713a37a8c06345a184650f0eb..aa4feec29980d344fdcf0623b81bd07590e06b9d 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -361,6 +361,14 @@ public class PaperWorldConfig {
         }
     }
 
+    public boolean seedBasedFeatureSearch = true;
+    public boolean seedBasedFeatureSearchLoadsChunks = true;
+    private void seedBasedFeatureSearch() {
+        seedBasedFeatureSearch = getBoolean("seed-based-feature-search", seedBasedFeatureSearch);
+        seedBasedFeatureSearchLoadsChunks = getBoolean("seed-based-feature-search-loads-chunks", seedBasedFeatureSearchLoadsChunks);
+        log("Feature search is based on seed: " + seedBasedFeatureSearch + ", loads chunks:" + seedBasedFeatureSearchLoadsChunks);
+    }
+
     public int maxCollisionsPerEntity;
     private void maxEntityCollision() {
         maxCollisionsPerEntity = getInt( "max-entity-collisions", this.spigotConfig.getInt("max-entity-collisions", 8) );
diff --git a/src/main/java/net/minecraft/world/level/levelgen/feature/StructureFeature.java b/src/main/java/net/minecraft/world/level/levelgen/feature/StructureFeature.java
index 3878a7f6402a1dff1e019e16dd8772ec7303ebe7..ef77b7e54c9ce3379b3bd6991aebcb4889029907 100644
--- a/src/main/java/net/minecraft/world/level/levelgen/feature/StructureFeature.java
+++ b/src/main/java/net/minecraft/world/level/levelgen/feature/StructureFeature.java
@@ -171,7 +171,24 @@ public abstract class StructureFeature<C extends FeatureConfiguration> {
                         if (!world.getWorldBorder().isChunkInBounds(chunkPos.x, chunkPos.z)) { continue; } // Paper
                         boolean bl3 = world.getBiomeManager().getPrimaryBiomeAtChunk(chunkPos).getGenerationSettings().isValidStart(this);
                         if (bl3) {
-                            ChunkAccess chunkAccess = world.getChunk(chunkPos.x, chunkPos.z, ChunkStatus.STRUCTURE_STARTS);
+                            // Paper start - seed based feature search
+                            ChunkAccess chunkAccess = null;
+                            if (structureAccessor.getWorld().paperConfig.seedBasedFeatureSearch) {
+                                Biome biomeBase = structureAccessor.getWorld().getBiomeManager().getBiome(new BlockPos(chunkPos.getMinBlockX() + 9, 0, chunkPos.getMinBlockZ() + 9));
+                                if (!biomeBase.getGenerationSettings().isValidStart(this)) {
+                                    continue;
+                                }
+                                if (!structureAccessor.getWorld().paperConfig.seedBasedFeatureSearchLoadsChunks) {
+                                    chunkAccess = structureAccessor.getWorld().getChunkIfLoaded(chunkPos.x, chunkPos.z);
+                                    if (chunkAccess == null) {
+                                        return chunkPos.getWorldPosition().offset(8, searchStartPos.getY(), 8);
+                                    }
+                                }
+                            }
+                            if (chunkAccess == null) {
+                                chunkAccess = world.getChunk(chunkPos.x, chunkPos.z, ChunkStatus.STRUCTURE_STARTS);
+                            }
+                            // Paper end
                             StructureStart<?> structureStart = structureAccessor.getStartForFeature(SectionPos.bottomOf(chunkAccess), this, chunkAccess);
                             if (structureStart != null && structureStart.isValid()) {
                                 if (skipExistingChunks && structureStart.canBeReferenced()) {