This post is for those who want to use Snopek’s Godot Rollback addon with the Steam’s peer-to-peer multiplayer APIs. I will cover both Relayed and True P2P. This tutorial was made on Godot 4.6.2, if it breaks on a later version or you encounter any problems in general, please reach out to me at brogolem35@protonmail.com.

I will be using a Godot 4 port of Snopek’s example project from his tutorials. I would highly recommend for you to watch his videos first before proceeding. The port in question can be found in this repo.

Relayed vs True P2P

Relayed P2P

• Packets are relayed over the Valve’s servers. (Adds delay)
• Doesn’t require hole punching.
• Can be used with GodotSteam’s SteamMultiplayerPeer. Supports RPC and stuff.
• Much easier to work with.

True P2P

• Also referred to as mesh.
• No relay/middleman. (Minimum delay)
• Requires hole punching and leaks IP. (It can be disabled at Settings>In Game>More>Steam Networking, will use relayed when disabled)
• Steam falls back to relayed P2P if the hole punching fails or if it is disabled.
• Steam’s legacy multiplayer API is needed to be used.
• Can’t use RPC. Rawdog the packets, like the God intended.
• The one we are using on Flame Up.

I personally recommend you to try the relayed method first and see if the delay is tolerable or not. Switch to true P2P if the relayed method is not tolerable. Even if you intend to directly jump to true P2P, you should still follow the relayed part as I will do some setting up there.

Relayed P2P

Add the GodotSteam addon from the AssetLib and reload the editor.

Create a SteamManager.gd file, fill it with the contents given here and add it as an Autoload.

Main.gd

Add two methods that connect to Steam.lobby_created and Steam.lobby_joined on _ready. Fill these methods as given here.

Change the contents of _on_ServerButton_pressed and _on_ClientButton_pressed as given here.

And you are set. Pressing the Server button will now host a lobby and your clipboard will be set to the lobby ID.

Result

The resulting repo should look like this.

True P2P

Now, the horrors.

Shoutouts to hislittlecuzin’s example. I wouldn’t be able to pull this off without it.

SteamManager.gd

Change the whole contests of it with the contents given here.

The biggest changes are the connection of _on_p2p_session_request and _on_p2p_session_connect_fail, and the addition of read_all_p2p_packets and send_p2p_packet. These methods make use of the legacy multiplayer API and packets sent with these methods are not relayed if the hole punching succeeds, otherwise they fall back to relaying. I highly encourage you to read the code yourself, it is quite documented. You will see some errors in the code now, they should disappear after the next section.

CustomMessageSerializer.gd

Change the whole contests of it with the contents given here.

class_name is given to make working with the static functions and enums easier.

MessageType enum is created to tag the different types of messages we will be serializing.

serialize_message and unserialize_message methods are overridden to make the input messages distinguishable from the other types of messages we will send.

Serialize and unserialize methods for messages such as ping, start, and stop exist to allow us to have these basic functionalities where we took them as granted while we were using MultiplayerPeer.

Feel free to add your own message types here when you are building your own game. I have some other types of messages in my game as well.

SteamAdapter.gd

Create this file and fill it with the contents here. Set network/rollback/classes/network_adaptor setting to it.

SteamAdapter overrides many of the functionalities of the default network adapter and forces the SyncManager to use the Steam networking APIs we have set up instead of RPC.

If you look closely to the is_network_master_for_node method, you will see that we get a field named steam_mp_id, which doesn’t actually exists. At least not now. We will resolve this in the future sections and I will explain what it is and why it is needed.

Main.gd

Remove signal connection relayed to multiplayer API at the _ready. We won’t use them.

Connect Steam.lobby_chat_update signal and add the method from here.

Add the start_game method and rewrite the _on_lobby_created and _on_lobby_joined like here.

Remove anything relating to the multiplayer API and replace multiplayer_authority instances with steam_mp_id, if there are any.

Project Wide

steam_mp_id is our variant of the multiplayer_authority and it is what dictates which player controls what node. The reason why we use our own value instead of the existing multiplayer_authority is that the multiplayer_authority internally keeps the IDs as 32-bit integers while the Steam user IDs are 64-bits. This causes an implicit downcast at the API boundary and can cause data loss. To avoid this, we must add our own property to the nodes.

Replace all, and I mean ALL, instances of multiplayer_authority with steam_mp_id, including the ones in the addons.

Add an int field named steam_mp_id to all nodes in the network_sync group. Make the values of those that are not player controlled 0 and the player controlled ones 1 by default to avoid breaking the single player. This includes addon provided ones such as NetworkAnimationPlayer. The ones you have missed will reveal themselves during the tests.

Result

The resulting repo should look like this.

Shameless Self-promotion

Checkout my game, Flame Up. It was where I developed and tested the methods I showed above. Feel free to try out the demo and wishlist it.