The difficulty in simulating fire when it’s outside the reality bubble is related to the simple fact that it can spread. As such this leads to a couple of different solutions with a couple of problems each. Here’s the basic list:
Solution: Fully simulate fire wherever it is until it burns out.
Problems: Once you start a forest fire or other large fire it might be a long time before the lag from it goes away.
Solution: Fully simulate only the submaps that have fire in them.
Problems: Fire will hit the edges of the submaps and stop, resulting in strange straight lines when the player returns. Also still some of the same lag problems.
Solution: Extinguish fires always.
Problems: Base catches on fire, player walks into the basement and walks back. Every fire is out and no damage has spread.
Solution: Wait until the player gets near to update a fire and retroactively find what it would have burned.
Problems: Player approaches old forest fire submap. Suddenly the entire forest flashes to ash (or a raging fire) around them when the old fire tiles are fast-forwarded.
The solution that I personally think covers the problem the best would be to occasionally reload fire maps and run a rough “fast-forward” style fire algorithm that is rougher but runs faster. That would mean large fires off-screen would still burn roughly as they would if you were there, while not providing too much lag in most cases.
