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 568da8f2ef3c5e1412cf13c10b425100af75e902..7ef45c941dacaa1f5cc4f0544af9ec76424cc783 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -417,6 +417,14 @@ 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 d7129f3379f2edecbcfd85f83d75e4d7064ce71d..7705ad4460ddf5166d922888f3a1368c50bb11ca 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()) {