An old question? Where to calculation collision?

Networking & Multiplayer
#1

I’m working on a multiplayer asteroids style game, a demo is web startable from:

http://www.cokeandcode.com/astroprime

Currently each client maintains a picture of the arena they are playing in. Each client sends updates of their player N times a second (currently N = 10) to the server. The server then broadcasts the state of all the players to all the players M times a second (currently M = 10).

Although I’m going to add stuff about only sending updates based on changes but this currently seems to work fine for a small number of players just flying around.

I’ve just started implementing the ships shooting. My orignal idea was to let the status of the ships (e.g. is the fire button pressed) let each of the players know when shots should be produced. This would mean that although the shots wouldn’t be perfectly synchonized, it would be [good enough ™].

Starting to think about collisions, where to perform the caculation and the assocaited health decrement?

I seem to have 3 options:

  1. Maintain a full picture on the server. Every single shot that gets produced, is only produced on the server. All collision detection goes on there. This seems great from a consistancy point of view, but with the overhead of sending message for each shot (and possible maintaining movement?)

  2. Each client produces shots for itself, only shots that hit the player on its host machine count. This means that only shots the player “sees” shots hit them actually do damage. Of course, nothing is consistant now. Also, how to handle non-player controled objects. [Also prone to cheats]

  3. Some sort of halfway house, maybe players report what they see and server takes what most people “saw”. Not quite sure about this, maybe some more refinement.

Currently my fave is number 2, since it fits with the way things currently work.

I’d really appreciate feedback/ideas/pointers…

Thanks,

Kev

#2

Other multiplayer games like Quake maintain shots (e.g. rockets) as separate objects on the server so the position of shots is updated by the server and broadcast to clients. The server decides who gets hit.

P.S.
Don’t get me started on how client side prediction (needed for smooth internet play) ruins the game --you dodge a shot as far as your view is concerned but you got hit from the server point of view. (This is a separate issue from general network lag.)

#3

[quote]P.S.
Don’t get me started on how client side prediction (needed for smooth internet play) ruins the game --you dodge a shot as far as your view is concerned but you got hit from the server point of view. (This is a separate issue from general network lag.)
[/quote]
thats where time nudge comes in :smiley:

Client side prediction x ms into the future, effectively negating ping latency.
Doesn’t help with instant hit weapons; and projectile weapons fire will appear to instantly travel the 1st x ms of their flight from the originators gun.
Still, helps Q3 hpbs enormously.