sdlnetplay allows one to share a game session with another person. This will allow hotseat multiplayer games to be played over the internet.
Both players start the same game and sdlnetplay makes sure the games are simulated deterministically, passes input to eachother and synchronizes frame.
sdlnetplay sits between the game and SDL, OpenGL and the system. It does so by overriding calls to these APIs. For instance, it uses SDL_GL_SwapBuffers and glBegin to synchronize frames. It makes sure the time, clock and gettimeofday functions always return the same value for both systems. It also makes sure rand returns a pseudo-random value that is the same for each client.
It uses LD_PRELOAD to override the API functions.
This project goes with a disclaimer that it is highly experimental. Most games will not work due to non-deteministic behavior that sdlnetplay cannot handle, usually caused by the game-logic relying on different threads. In addition, sdlnetplay currently has a nasty way to detect desyncs by storing screenshots to disk, hashing the file and send over and compare the hash of the other system.
Also note that because most Linux games are compiled to 32-bit binaries, this library also compiles to 32-bit by default, otherwise it would be incompatible with the game and will not be able to preload.
Games that have shown to work:
- Gish
Games that have issues:
- Aquaria
- Desyncs after audio dialogs, which runs on a separate thread
Games that break down quickly:
- FTL
- OpenGL
- SDL 1.2
- libc6-dev-i386
- imagemagick
make
On one system host a game:
SDLNETPLAY_LISTEN=1 LD_PRELOAD=/path/to/sdlnetplay.so /path/to/game_executable
On another system you need to connect to the host:
SDLNETPLAY_CONNECT=1 SDLNETPLAY_HOSTNAME=hostname.of.other.player LD_PRELOAD/path/to/sdlnetplay.so /path/to/game_executable
The protocol uses TCP port 8008, so make sure the client can reach the host on this port.