TrackFastRack

A tiny standalone Forge 1.20.1 mod that isolates the track placing / breaking flood-fill optimisation from the stacode123/Create fork and re-applies it to the published Create mod via a Mixin.

The fix

It targets TrackGraph#findDisconnectedGraphs(LevelAccessor, Map) in com.simibubi.create.content.trains.graph.TrackGraph. This method runs a connected-component flood fill every time a track is placed or removed.

The released Create (≤ 6.0.8) implements the BFS frontier as an ArrayList and pops from the head with ArrayList#remove(0), which shifts the whole backing array on every pop. That makes the flood fill O(n²) — on a large network (~80k nodes) a single track change walks billions of elements. This mod swaps the frontier for an ArrayDeque (poll() is O(1)) and replaces stream().findFirst() with a plain iterator, making it O(n). The change comes from fork commit 272e97604 ("Optimise train network hot paths").

How it works

• dev/stacode/trackfastrack/mixin/TrackGraphMixin uses @Overwrite to replace the method body, with @Shadow declarations for the members it needs (nodes, locateNode, getConnectionsFrom, transfer, setId, setNetId).
• All @Shadow/@Overwrite annotations are remap = false — the target is a third-party mod class (not Minecraft), so nothing needs obfuscation remapping.
• The mixin deliberately lives in dev.stacode.trackfastrack.mixin, not in Create's package: bundling classes into com.simibubi.create.* triggers a JPMS split-package error at launch (Modules create and trackfastrack export package ... to module ponder). Package-private access instead goes through @Shadow (public methods) and TARGET#setNetId(...) (instead of writing the package-private netId field directly).

Build

Requires JDK 17+ and network access (it resolves Create, Ponder and Catnip from https://maven.createmod.net).

./gradlew build          # produces build/libs/trackfastrack-1.0.0.jar
./gradlew runServer      # dev server with the mixin active

Install

Drop the built jar into a Forge 1.20.1 mods/ folder alongside Create 6.0.x. The mod declares a required dependency on create (≥ 6.0.6) so it will not load without Create.

Verification

On game start the mod runs a tiny smoke test: it loads TrackGraph (forcing the mixin apply) and calls the replaced method once, logging TrackGraph flood-fill self-test OK. A clean line proves the @Overwrite bound to the target method at runtime.