Load the LOD world engine off the render thread on level reload (fix join freeze)

[Kishku7]

Summary

LevelRenderer.allChanged builds the Voxy renderer synchronously, which opens and indexes the per-world LOD store (RocksDB open + Mapper/palette load) on the render thread. For a large store this freezes the client for several seconds on every join / dimension change.

Fix

Build the WorldEngine on a background thread, then create the GL-bound VoxyRenderSystem back on the render thread once it's ready. A generation counter (bumped on every shutdown/create, all on the render thread) lets an in-flight load detect that it has been superseded by a level change / disconnect / reload and discard itself safely. The GL object is still created on the render thread; only the disk I/O moves off it.

Scope / testing

One file (MixinLevelRenderer). Tested on MC 26.1.2 with a large LOD store (alongside VoxyServer): the join freeze is eliminated; LODs fill in a moment later as the engine finishes loading.

Note for maintainer

VoxyInstance.getOrCreate still holds its StampedLock write lock across the build - now off the render thread, so it no longer freezes rendering, but it can briefly block other getOrCreate callers (e.g. ingest) during the first load. Relaxing that lock is a deeper change left out of scope here.

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Happy to discuss any of this - you can reach me on my Discord: https://discord.gg/2ZxzbCzAHe

[wahfl2]

you can reach me on my Discord

Cortex has a discord server, that's probably where this should be discussed: https://discord.gg/teErFatQv9