[gameprogrammer] Re: pingin'

[Jake Briggs <jakbri@coretech.co.nz>]

Yasser Gonzalez Soto wrote:
> I want make an application (c++ or delphi) that pings to an ip 
> address. Is reponse add a "IP actived" message to a list

Well you could just try to open a socket on the remote IP.... Depends 
what libraries you are using.

> second:
> In a multiplayer LAN game using tcp/ip,  I want make a game where, 
> each time an user connects to the server, creates a sprite on the 
> room. So, when a player on his own PC moves his character screen 
> moves, on the other PC else, user player moves. Could you give a clue

Well here is how I'd do it, in the simplest way I can think :

1: You would have the server remember the state (x and y position, for 
example) of each client.
2: The client would request a move - "Hey server, I want to move to x 
position,y position".
3: The server would validate the request, checking that the move is 
valid based on the clients previous location. If it is, the server 
updates its internal state.
4: The server updates each client periodically with the state of all the 
clients.

So we have a situation where each client puts sprites (including its 
own) wherever the server tells it to. If a client gets a key press from 
the user that means "move up 1 pixel", it doesn't move its own sprite - 
it tells the server that it wants to move its own sprite up one pixel. 
The client only moves sprites when the server tells it too. The client 
doesn't change the state of the game (it doesn't change the position of 
sprites) unless told to by the server. Deferring to the server this way 
keeps things nice and tidy, since you have separated the 
responsibilities of the client and server cleanly - they won't step on 
each others toes.

There are probably about 100 ways to do this though, and this way will 
have issues that need to be worked around later. For example, if ping 
time (lag) is high, the user will notice a lag when moving. They hit the 
"up" button and half to wait half a second to see their sprite move. A 
way to work around this specific issue is to implement client-side 
prediction. This means that the client does move its own sprite (and 
possibly other players sprites) to keeps things looking good to the 
user, but will still use the servers version of the game state as the 
official state placing the sprites where the server thinks they should be.

Right gameprogrammer mailing list, I expect my little scheme to be 
ripped apart :)

--
Jacob Briggs
Systems Engineer

Core Technology Limited
Level 1, NZX Centre
11 Cable Street
Wellington
Phone +64 4 801 2252

--

object doAnythingConceivable(string whatToDo, object whatToDoItWith) { .....



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