Some Structuren BoundingBoxes have a weird offset

[fantahund]

Expected behavior

Some structures return an incorrect position of the bounding box.
The following structures usually return the bounding box too high:
Cold Ocean Ruins, WarmOcean Ruins, Beached Shipwreck, Shipwreck, Buried Treasure
The following structures usually return bounding boxes that are too low:
Jungle Pyramid, Igloo
All other structures seem to be correct.

The problem only seems to occur in newly created chunks. After a server restart, the bounding box is displayed correctly.

Observed/Actual behavior

Newly loaded chunk:

After a server restart:

Steps/models to reproduce

• Install the StructureBoundingBoxTestPlugin.
• Go to the structure described in the problem above. And see at which position the bounding box with diamond blocks is displayed.
• Restart the server and go to the same structure and the bounding box seems to be in the right place.

Plugin and Datapack List

[12:07:15 INFO]: Server Plugins (1):
[12:07:15 INFO]: Bukkit Plugins:
[12:07:15 INFO]: - StructureBoundingBoxTestPlugin

[12:07:54 INFO]: There are 3 data pack(s) enabled: [vanilla (built-in)], [file/bukkit (world)], [paper (built-in)]
[12:07:54 INFO]: There are no more data packs available

Paper version

[12:08:25 INFO]: Checking version, please wait...
[12:08:25 INFO]: This server is running Paper version 1.21-37-master@dd49fba (2024-06-24T02:08:49Z) (Implementing API version 1.21-R0.1-SNAPSHOT)
You are running the latest version

Other

No response

[Kadeluxe]

Just discovered this bug on 1.20 too so it's not 1.21 specific.

[jugh3ad]

This is vanilla behavior for the way some structures are created during initial chunks creation. The initial bounding box has a hardcoded Y level. After the terrain is generated the structure is moved to the appropriate Y level of the structure.

[lynxplay]

As jugh3ad correctly pointed out, that is simply how some structure pieces generate.
We could make this interaction a little bit less painful by clearing the structure BB cache after the StructureStart is done with postProcessing, but I am hoping for some more input from the team here.

E.g.

diff --git a/src/main/java/net/minecraft/world/level/levelgen/structure/StructureStart.java b/src/main/java/net/minecraft/world/level/levelgen/structure/StructureStart.java
index c92a2c5bb..fbbc0f0e0 100644
--- a/src/main/java/net/minecraft/world/level/levelgen/structure/StructureStart.java
+++ b/src/main/java/net/minecraft/world/level/levelgen/structure/StructureStart.java
@@ -121,6 +121,7 @@ public final class StructureStart {
             }
             // CraftBukkit end

+            this.cachedBoundingBox = null; // Paper - invalidate cached bounding box after post processing pieces.
             this.structure.afterPlace(world, structureAccessor, chunkGenerator, random, chunkBox, chunkPos, this.pieceContainer);
         }
     }

would fix the bounding box after place. It'll still be fucked during the respective async events, but I don't think we really want to edit anything there.

[NickCloudAT]

Just came across this issue while making a plugin that needs to check if a player is inside a structure.
It would be VERY neat if this was going to be changed.. Currently I need to calculate/fix the position myself as good as I can but natively would be so much better.