netplay: patch export globals and sync them

[JerwuQu]

Solves #649 and #542.

Tested with the cart from #542 (comment).

I understand if this is not the direction you wanna go and maybe something should be done differently, but it's a start at finally getting this fixed :)

[aduros]

I like the idea of preprocessing the wasm to export globals, but using JSON in the serialization seems inefficient.

I wonder if we can assume that the entire globals section is a known fixed size and ordering. Then we'd only need to write the values into the saved state. I think we could also write each value as binary, the exact type also being known. What do you think?

[JerwuQu]

Unfortunately I don't think we can get globals as binary data from JS and would have to convert it back and forth from JS types ourselves. At that point I'd guess the browser implementation of JSON isn't actually slower and is a lot less code.

I'd agree with looking into fancier solutions if we serialized this often, but to my knowledge it's only on client connections and user savestates (?)

Feel free to look into it! I'm pretty happy with the WASM patcher code but for the State-code I just made something that works :)

[aduros]

I'd agree with looking into fancier solutions if we serialized this often, but to my knowledge it's only on client connections and user savestates (?)

For netplay we serialize the state every frame, and rollbacks can result in multiple unserialize/serializes in a single frame. Not a huge deal, but it would be good to optimize later 🙂 Let's merge it for now to unblock wasm languages that rely on globals.