8 ms·

What happens if you cancel the event on computer A but it takes 500ms to reach computer B and in that time B has seen their troops and attacked?

by eddsh1994 4y ago

rcme 4y ago
You probably just accept that that’s possible. There are ways going to be conflicts in systems with distributed state. How you handle it depends a lot on the specific application and how often it happens.
Centigonal 4y ago
This post[1] talks about the mechanics of implementing this netcode. The scenario you're talking about would be a "desync," where in your simulation, the opponent never saw you, but in the opponent's sim, they did. You really don't want that, as that quickly makes the game diverge and become unplayable. What most games that use this technique do is "lockstep" - they send out a chunk of commands called a "frame" several times a second, and step the simulation forward to step n only when they have frame n from every player. So, in your scenario, if player A cancels before troops are visible to player B, then player B's computer won't ever show the troops, because simulation B will have paused during the 500ms of network lag, since it didn't have the frame from player A. [1] https://news.ycombinator.com/item?id=34395153 https://news.ycombinator.com/item?id=34395153
- rcme 4y ago
  It’s worth noting that often lockstep is not appropriate. Fighting games, for instance, require frame-perfect inputs. Fighting games become hard to play perfectly if you introduce jitter into the timing by requiring frame synchronization. In a fighting you’d just unwind whatever happened and replay the simulation as if the “real” thing happened, which could mean undoing things a user saw in certain circumstances.
  - Centigonal 4y ago
    That's true - I haven't seen lockstep used outside of RTSs.
    - comex 4y ago
      Many fighting games did and do use lockstep; it’s only recently that rollback has started to become the norm, and some recent big releases still don’t have it. But fans actively clamor for rollback because it’s a far superior experience.

What happens if you cancel the event on computer A but it takes 500ms to reach computer B and in that time B has seen their troops and attacked?

rcme 4y ago

You probably just accept that that’s possible. There are ways going to be conflicts in systems with distributed state. How you handle it depends a lot on the specific application and how often it happens.

Centigonal 4y ago

This post[1] talks about the mechanics of implementing this netcode. The scenario you're talking about would be a "desync," where in your simulation, the opponent never saw you, but in the opponent's sim, they did. You really don't want that, as that quickly makes the game diverge and become unplayable. What most games that use this technique do is "lockstep" - they send out a chunk of commands called a "frame" several times a second, and step the simulation forward to step n only when they have frame n from every player. So, in your scenario, if player A cancels before troops are visible to player B, then player B's computer won't ever show the troops, because simulation B will have paused during the 500ms of network lag, since it didn't have the frame from player A. [1] https://news.ycombinator.com/item?id=34395153 https://news.ycombinator.com/item?id=34395153

rcme 4y ago
It’s worth noting that often lockstep is not appropriate. Fighting games, for instance, require frame-perfect inputs. Fighting games become hard to play perfectly if you introduce jitter into the timing by requiring frame synchronization. In a fighting you’d just unwind whatever happened and replay the simulation as if the “real” thing happened, which could mean undoing things a user saw in certain circumstances.
- Centigonal 4y ago
  That's true - I haven't seen lockstep used outside of RTSs.
  - comex 4y ago
    Many fighting games did and do use lockstep; it’s only recently that rollback has started to become the norm, and some recent big releases still don’t have it. But fans actively clamor for rollback because it’s a far superior experience.