Player-to-player messages

Player-to-player (p2p) messages are a useful mechanism when creating more advanced games. A p2p message is essentially a "packet" with an ID and a few arguments.

Sending p2ps

You can send p2p messages by calling gms_p2p_send. It requires a player_id to whom the message will be sent, an id, and optionally up to 14 arguments. You can choose the ID to be anything between 0 and 255. It's useful to make macros for these IDs, so that you can easily see what an ID is supposed to do. In my examples, I always add macros prefixed with p2p_.

Receiving p2ps

To receive p2ps you'll need to set a script using gms_script_set_p2p. That script will be called whenever the game receives a p2p message from another player. The general structure of that script should look something like this:

var mid = argument0, sender = argument1, args = argument2;
switch mid
    case p2p_first:
    case p2p_second:
        show_error("Unknown p2p message with message id " + string(mid) + " received!", true)

The piece of code between the case [id]: and the break statement is the code that will be executed when a p2p message with that id is received. I'll annotate future code with just '// p2p_...' to keep it readable. It should be inside the p2p script, inside the switch-statement.

Example use-cases

Keeping kill count
So you want to keep track of how many kills everyone makes. You'll need a way to let the killer know that he killed someone. You can do this by sending a p2p message whenever a player dies to its killer. For example:

// obj_player, event: collision with synced bullet

gms_p2p_send(p2p_got_kill, other.owner) // other.owner is automatically set by the extension

// p2p_got_kill, inside p2p script:

show_message("I killed " + string(gms_other_get(sender, 'name')) + "!")
score += 1 // Or whatever else you want to do

Special sending targets

Since update GameMaker Server supports sending P2P messages to more than one player at a time. The following special values can be used instead of a player_id:

  • gms_p2p_all_in_room - sends the message to all players in the same room as you

  • gms_p2p_all_in_session - sends the message to all players in the same session

  • gms_p2p_all_in_game - sends the message to all players in your game that are running the same game version, which you set in gms_settings

Note in particular 'gms_p2p_all_in_game', which can now be used to communicate across different sessions. One use case for this might be broadcasting global admin messages.

Replies (4)

Last message on 5 Jun 2017

amkgames on 5 Apr 2015, 21:21:01
What is player ro player message? Is it whisper? Or PM?
Forgeio on 5 Jun 2017, 05:38:09
It's actually not an actual message that you would send to someone, it is a way of sending data to (an)other player(s) instead of to the server.
Size43 (Administrator) on 6 Apr 2015, 11:17:46
It's a way to send a custom message to another player. It's not a chat message, but a set of values that can be strings or doubles.
amkgames on 5 Apr 2015, 21:21:24
I mean To*