Xaero's Map Bug: Train Tracks Overlay Persist Across Worlds

Hey fellow Minecraft adventurers! Today, we're diving into a peculiar issue that's been popping up in the TerraFirmaGreg modpack, specifically with version 0.11.10. It seems like Xaero's World Map is holding onto memories, and not the good kind! Imagine this: you're happily building your intricate railway system in one world, enjoying the visual representation on your map. Then, you hop over to a brand new world, ready for a fresh start, only to find ghostly train tracks from your previous adventure still haunting your map overlay. This persistent overlay bug can be quite confusing, breaking the immersion and making it harder to navigate your current world. We're exploring this bug, its potential causes, and what we can do about it.

Understanding the Persistent Train Track Overlay

This particular bug centers around the train track overlay feature in Xaero's World Map. Normally, when you switch between different Minecraft worlds, the map should update its displayed overlays to reflect the content of the current world you're playing in. This is crucial for maintaining accuracy and preventing visual clutter. However, in this reported instance, when a player loads a new world after having a world with create train lines, the overlay for those train lines persists. This means that even though you're in a completely different world, possibly with no create mod installed or no train lines built, you're still seeing the old tracks overlaid on your map. This can be incredibly disorienting. For instance, if you were working on a massive railway network in one save and then decided to start a new survival world, you'd expect your map to be clean, showing only the terrain of your new world. Instead, you might see a spaghetti of lines from your previous endeavor, making it difficult to discern your current location or any new structures you're building. The original report mentions this occurring in a single-player environment, which often simplifies troubleshooting, but it also notes a potential relevant detail: the previous world where the train lines were present was a server. This detail might be a key factor in why the overlay isn't resetting correctly. The core issue is that the modpack or Xaero's World Map isn't properly clearing or unloading the overlay data when transitioning between worlds, especially when one of those worlds was previously connected to a server. It's like leaving a sticky note on your monitor and then moving to a new office – the note is still there, even though it refers to your old desk.

Why is this Xaero's Map Bug Happening?

The root cause of this persistent overlay bug likely lies in how Xaero's World Map handles the loading and unloading of world-specific data, particularly when interacting with the create mod's train lines. When you generate a world map, Xaero's downloads or generates data pertaining to that specific world. This includes terrain, waypoints, and, in this case, specific mod-added elements like train tracks. The create mod, with its sophisticated train system, generates a lot of unique data points that Xaero's Map needs to interpret and render. The problem arises during the world transition. Ideally, upon quitting a world and loading a new one, all data associated with the previous world's overlays should be flushed or marked as inactive. However, it appears that in certain scenarios, this cleanup process isn't happening effectively. The mention of the previous world being a server is particularly interesting. Multiplayer environments often have different data handling mechanisms than single-player. It's possible that when transitioning from a server world (even if played in single-player mode afterward, or if the transition is from a server world to a new single-player world) to a new single-player world, the map doesn't correctly de-register the server world's overlay data. This could be due to how server clients handle persistent data versus how a purely local single-player world does. Xaero's World Map might be caching this data more aggressively than intended, or there might be a conflict in how the create mod's data is flagged for removal upon world exit. A potential scenario is that the overlay data is tied to a world instance rather than a world save, and when the instance is swapped, the old data isn't fully discarded. This is a common challenge in game development: ensuring that resources and data are correctly managed and released when transitioning between different game states or environments. The game needs to be told,