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How to setup and run multiplayer sessions.

Introduction

Racer is actually always running in multiplayer mode; it connects to itself, so the program is both client and server if run as single player.

The Lobby

Racer has a built-in lobby. When entering the lobby you connect to a Lobbyserver (currently I have one setup on the internet, available as lobby.racer.nl). The lobby is the place if you want to race over the internet.

The lobbyserver is installed in the same directory as Racer itself, so you can a Lobbyserver yourself, either locally for a LAN environment, or on the internet to provide an alternative to Racer's default lobby. Currently the lobby at racer.nl isn't too crowded so there doesn't seem a need for this yet.

Automated server

Racer v0.8.7 first supported an automated server. This allows a bot to connect to the lobbyserver and start hosting races. This is useful so you can have multiple unattended computers out there on the internet, all running as a dedicated Racer multiplayer server to which players can connect.

More info on setting up such a server at your own home can be found here.

Multiplayer over LAN

Important to make sure is:

• For multiplayer to work you need to be able to get to the other computers. For a LAN, this should pose no problem, if you can ping the machines that would want to connect. For the internet, a router might impose a problem.
• Racer uses a single port currently to do all the communication. Make sure the firewall let's Racer connect outward on this UDP port. The port is specified in racer.ini:multiplayer.port (normally 25000).
• Both clients and server must have the tracks and cars that are about to be raced on!

Last but not least, realise that multiplayer is a work in progress, lots of things will be wrong with it (version 0.5.2 beta 7.5 currently). Things like collisions are not working well (if at all).

Settings

You won't need to touch most of the settings in racer.ini directly. For Mac users, no dialog pops up when trying to join a race though; you need to modify multiplayer.server_remote to the IP address (or name) of the server you wish to connect to. After that, run the game and click 'Join MP game'.

One feature of multiplayer is the spectator view; you can turn that on by setting multiplayer.audience to 1. This way, no car will be loaded for this client, and you can only watch other cars drive.

RUNNING FROM BEHIND A ROUTER

It depends on what you want to do, join or host a game. If you want to connect to another client (join), you might not need to do anything. Although this is UDP, so I'm not sure how routers deal with UDP connections going out. You may want to check if you firewall allows outgoing packets on Racer's multiplayer port (mostly 25000, see racer.ini:multiplayer.port).
For a server, you would only be able to do 1 server probably. Then have your clients (the remote car drivers) connect to the IP address of your router (the IP address that is actually reachable on the internet, for example 194.109.6.92). You need to forward UDP port 25000 then to your internal address (i.e. 192.168.0.1), which is a rule to be placed on the router, through a NAT table for example, or using ip forwarding on Linux.

That might do it. The downside is that you can only run 1 server behind your router, since incoming packets on UDP:25000 is something the router doesn't know who to send to, unless you explicitly tell it to.

If you have remarks about this text (I have never tried Racer behind a router), let me know. Setting up multiplayer games may be tough in practice.

THE PROCEDURE (LAN multiplayer)

Assuming everything is in place:

• The host starts the game, and clicks 'Host multiplayer game' from the menu.
• On the client, select 'Join multiplayer game' and enter the name or IP address (like 192.168.0.1) of the server.
• The server should print out some comments in its console that the client is trying to reach the server.
• You should now both be on the track.
• To close down, press ESC on the client. This will close the connection, and the car should disappear from the server.

TROUBLESHOOTING

• Can't connect; try pinging the machine you want to connect to. Open up a shell and type 'ping <hostname>'. If no connection can be established, perhaps the firewall is withholding ICMP network messages but most of the time you just can't reach the other host.

Happy racing!

(last updated November 13, 2012 )