Portal 2 Multiplayer Patch Plugin

This repository contains the source code for a Source engine plugin which is aimed at allowing an arbitrary number of players to join and play in both the singleplayer and cooperative campaign at the same time. It does so using only generic patches, without the need for any map-specific support scripts, as well as by only making the minimum number of changes required for the maps to be playable.

Currently, the plugin only works on Linux. Windows support is theoretically possible (the plugin foundation code does contain initial untested Windows support code), however as the Windows release of Portal 2 was compiled with an entirely different compiler (MSVC vs GCC), all patches would have to be adjusted to work on Windows. If you want to help out by doing this yourself, please let me know - I will gladly assist you throughout the process, and merge your work once you finish. To get started, see plugin/src/anchors.cpp and the offsets / orig-sequences in the actual patches.

Patches include:

• removing the player cap from all multiplayer game session
• removing the partner-disconnect check
• a rewritten transition ready-tracking system, which ensures that map transitions work with an arbitrary number of players both in singleplayer as well as in coop maps
• changes to the spawning logic for singleplayer maps when played in a multiplayer session: point_teleport triggers will teleport all players when they're targeting !player. They will also update the spawnpoint as well, anchoring it to any moving surfaces. This causes the start elevator to work properly with multiple players.
• changes to the stuck-handling logic: if multiple players are stuck within each other, they temporarily loose collision with each other until they become unstuck
• for singleplayer maps: doors will open and close multiple times, to ensure that all players can go through them (including after respawns)
• env_fade entities will never affect all players in single player maps

Building

Alternatively, you can grab the latest release from here. Just place the p2mppatch.so file in the portal2 game directory if you do.

If you want to build from source, follow these steps:

• ensure you have cloned the repository recursively - if not, execute git submodule init and git submodule update
• download and setup the Steam runtime using the ./setup_runtime.sh script
• build the plugin by executing make in the plugin directory
• copy the resulting p2mppatch.so file into your game's portal2 directory

Usage

Simply load the plugin using the plugin_load p2mppatch console command while on the main menu - otherwise there is a high chance the game will crash. You can unload the plugin using plugin_unload p2mppatch once you're done using it. If the plugin is not loaded, your game will be unmodified, however the plugin was also designed to not interfere with regular gameplay even when loaded.

Once the plugin is loaded, start a regular CoOp session with one of the people you intend to play with. Afterwards, the other players can join using the connect <ip> console command (ensure that you have ports 27015 and 27031-27036 forwarded).