[cloutiertyler]

Just to copy in my response from there too:

I'm Tyler (guy in the video). In BitCraft we currently implement client-side prediction outside of SpacetimeDB.

However, we DO plan to add automatic client-side prediction as a feature for SpacetimeDB in the near-ish future! Because all your server-side logic is in Wasm modules, we plan to run an embedded version of SpacetimeDB to execute the server logic on the client. As long as the server and client agree on the changes to the data we can reconcile the transactions, otherwise we'll rollback. Notably, we can do this with only partial state on the client!

We can also do deterministic simulation if you have total knowledge of the game state with this solution as well.

[kriper]

How would you simulate physics, pathfinding, animation state on the server using this tech? Do you have to ditch your engine (do I have to reimplement what unity/unreal gives me for free?) ?

[ncr100]

Cool, jumping in as a noob to multiplayer dev, so currently for BitCraft MMORPG simulation, e.g. to prevent "god-mode flying", would be done outside the server.

Q How is that coordinated with the SpacetimeDB? Is there a penalty, or perhaps a correction applied to the malicious client (and replicated to listening clients) in the case a hacker modifies their movement illegally?

Tx for sharing your time btw!

[Rohansi]

Since SpacetimeDB would be your backend (game client <-> SpacetimeDB) you would need to verify the inputs to your reducers to prevent cheating. Not really different from anything else.

[zinlencer]

But that's completely different from how Unreal typically does it. Movement is client-side predicted and server authoritative out of the box. How does SpacetimeDB even know the collisions of my level?

If I were to cheat and disable all wall collisions on the client. An Unreal server would roll me back, to all other people it would look like I'm walking into the wall. How do you even get SpacetimeDB to run Unreal's runtime (because movement kind of depends on deterministic results for frames). How does SpacetimeDB get hold of the assets (collisions)?

[Rohansi]

I am also skeptical of SpacetimeDB for the same reason. There is no game engine helping you do any simulation and that makes development harder. Your (server-side) assets would somehow need to be synced to SpacetimeDB which possibly means you can't use your editor tools to design them anymore.

As a service backend+database the concept is cool and probably useful. But I don't see it being good at being a game server.

[whizzter]

Reading/hearing talks from people doing server backends there is many half insane things being done to keep servers and persistence in check, and everyone still a different custom solution.

A common scenarios:

- "Game-server" using "regular" server+DB frameworks, often works but seldom in real-time scenarios.

- Realtime Game-servers (with in-memory state, sometimes supporting rollback,etc) that then has persistence more or less as an afterthought (duplicating state management between client<->server<->persistence)

What spacetime tries to do (and my current experiment) is to merge the server and DB to move persistence _performance_ concerns into the backend process.

We _rightfully_ moved databases out of server processes for easier management and safety in the 90s, but since f.ex. SQLite has been a bit of a resurgence because the usercode was in a managed language and wasn't as likely to cause a corruption issue.

WASM is a great enabler here because it allows the server/DB to sandbox the logic-code even in "unsafe"/realtime languages from the more precarious DB parts of the process so we don't have to risk data-safety even as we move back to co-locating server-state and persistence data within the same process.

[Rohansi]

I have also experimented in this space but came to the conclusion that it's not good for games. Not necessarily because it's a bad idea but because it's not how games are made. To make a game with something like SpacetimeDB you would need to build a game engine. You'd also need to build out tooling for managing assets for the server.

One thing about SpacetimeDB that I'm not sure about is if reducers can run concurrently or not. I would hope so but it's very possible they don't and that can be a big regression vs. current game servers.