Track and expose latest confirmed tick

[elementbound]

✨ Description

Have a way to know which ticks are confirmed, as in known not to change. This could mean that e.g. the tick is past the history limit so it definitely won't be resimulated, or that all the inputs are known for that tick so there's no reason to resimulate that tick.

Use case

Game mechanics where cancelling an action would be suboptimal, e.g. player death. In this case, the player being despawned and suddenly thrown back into the game is jarring. Instead, the player could be incapacitated but still recording inputs, and once the server confirms death, the player is despawned.

Distribution

netfox core

Notes

• The base API could be a simple bool somewhere, with higher-level primitives optionally built on top of it, like Futures
• Make sure to consider partial inputs - e.g. one RBS is controlled by multiple players
• Also consider cases where a single player can control multiple RBS'
• Kudos @albertok for suggesting this!

[albertok]

I imagine the implementation would be along the lines of having NetworkRollback be a broker and expose functions to query the state of input.

NetworkRollback manages a dictionary of Node:latest_input_tick

RollbackSynchronizers in their input receivers update their latest received tick in a function call which takes their configured root and tick as argument.

NetworkRollback exposes some convenience functions or lets you read the entire dictionary.

NetworkRollback clears out anything with a tick older than history_limit.

I like this pattern because it allows a quick query and decision to take place. For example we don't need to know about everything in a given scenario - a projectile potentially doing a killing hit just needs to know if everyone in its proximity has submitted. It doesn't care what the state of a player on the other side of the map is.

In that scenario a projectile can keep checking the manifest each rollback loop and deciding when to do an irreversible action. ie, explode and tell the player hit this is a confirmed hit.