worldmapexplorer appears not to work properly anymore

[rezecib]

Previously each world object (there's one per overworld, caves, etc) had a "worldmapexplorer" entity attached to it that stored a "master copy" of the map, containing the sum of all exploration all players had made. This seems to not work properly anymore.

An idea for a new system building off of the cartography system the game now uses:

• For each world, listen for player despawns
• When a player despawns, save a hidden cartography map object with their map data.
• When another player despawns, their map object overwrites the previous one (assumption: they have managed to sync with all stored maps).
• Also listen for player spawns. When a player spawns in, load in the map data from the hidden object.

Possible defense against breaking the assumption of having synced:

• Version the map data.
• Initially, player map version is 0.
• When a player despawns, they first sync in any saved map data, then save their map data.
  • The saved map version becomes max(player_map_version, previous_saved_map_version) + 1
• When a player loads in:
  • Check for players in the world, and find the one with the highest map version number, saving their map.
  • This covers the case where player A has been in the world exploring, but hasn't despawned and saved their map, and a new joining player B needs A's map data that they uncovered prior to B joining.
  • Do this at most once a second, to prevent a huge load spike if reloading a world with everyone still connected, for example.
  • Then sync with the saved map data and give the spawning player its version number.
• When syncing from the saved map, only sync if its version is greater than the player's.

I think this should result in consistent map saving without data loss.