Redo?

[fsharpn00b]

After using undo, is there any way to redo? Or are the history elements discarded on undo? Again, not a major issue.

[helloyork]

This sounds like an interesting idea, and one that should be implemented.

However, implementation is somewhat complex. For example, how user-defined scripts react to redo behavior is still undetermined.

Thanks for suggesting this feature! It may be implemented in the future.

[fsharpn00b]

For that matter, depending on what side effects they have, I could see user-defined scripts behaving in unexpected ways with undo. I'm guessing you've had to build something like a state monad, so that if the player undoes to a certain point, the state of the game is exactly what it what the last time they were there (i.e. there can't be any mutable state left over from before the undo.)

[helloyork]

Undo is possible because we've implemented a lot of special processing during user script execution (such as Abortify in ServiceHandlerCtx and cleanup functions in Script), allowing us to "interrupt" user scripts and revert to previous snapshots when needed.

However, Redo is more than just "running Undo again."

• We can restore the game's state from a snapshot, but user scripts often perform additional interactions, such as opening custom windows, displaying additional components, or mini-games.
• These items aren't part of the engine's core state, and snapshots can't be saved and restored at any time.
• External windows, React components, third-party services, timers, network requests, and so on aren't part of this state. Taking snapshots and replaying these items is almost impossible.
• Implementing Redo often means rerunning the user script, and it must be done instantly to ensure the external results are identical to the original. This places high demands on both the engine and the user script.

I have also considered providing additional APIs to allow users to define redo behavior in their scripts, but this would make the code more complicated, and users would have to handle various edge cases such as interruption/undo/redo.