SpaceWar with Godot

This project is a usage sample of rollback netcode using Backdash.Gns in Godot.

It shows a basic example of an online lobby using Steam P2P Matchmaking & Lobbies.

Video

backdash-gns-godot-sample-2.mp4

How does it work?

This creates and/or joins a Steam Lobby via ISteamMatchmaking interface.

When the host creates a Steam lobby, it sets some metadata about the lobby with ISteamMatchmaking.SetLobbyData().

• Key: "GameTitle"
  • Value: "BackdashGnsGodotSample"
    • This exists to filter out other game lobbies that uses the same test AppId 480
• Key: "LobbyName"
  • The name of the lobby This metadata is used in the browse lobby scene.

When a client enters the lobby, it sets some metadata about itself with ISteamMatchmaking.SetLobbyMemberData():

• Key: "Spectator"
  • Value: "1" - it's a spectator
  • Value: "0" - it's a player
• Key: "Ready"
  • Value: "1" - it's ready
  • Value: "0" - it's not ready

To start the game, the lobby owner sends a message with ISteamMatchmaking.SendLobbyChatMsg() when every player is ready.
This message consists of the players and spectators list:

• Magic string "BG" (2 bytes)
• Message kind (1 byte)
  • This is always 0, as we don't have any kind of message other than this "start game"
• Number of players (1 byte)
  • For each player:
    • Player's Steam ID (8 bytes)
• Number of spectators (1 byte)
  • For each spectator:
    • Spectator's Steam ID (8 bytes)

This protocol is very rudimentary, but it does the job for this simple demo.

Controls

• Arrows: Move
• Space: Fire
• Left Ctrl: Missile

Running

Client

You must be running the Steam client to run this sample.

On some platforms, you might need to create a steam_appid.txt that has only 480 written in it, in the executable's directory.