Quick question regarding multiplayer

For every room created there is a server and peers ?

Each room is "independant" regarding the others ? Can an event interact with another room ?

no.

The first client to "join" a room, is not 'just' joining it, he creates the actual room on the signalling server , then joins it. and instantly becomes "Host"

Clients that follow join the room and become "Peers".

Okay. So, to have it written as straightfoward as possible, for each room there are 1 host and X peers, right ?

Ah ! Another question while I'm here : the multiplayer objet can sync instances positions and variables.

So, what's the best way to synchronize attributes like visibility ?

Send a broadcast message to the peers, the peer receives it and changes the instance visibility ?

Or just to add an instance variable "visibility" on the object which will synchronize automatically, and add a global event (availble for the host and peers) like "if sprite visibility = true -> sprite ; set visible" ?

Okay. So, to have it written as straightfoward as possible, for each room there are 1 host and X peers, right ?

Yes

Ah ! Another question while I'm here : the multiplayer objet can sync instances positions and variables.

So, what's the best way to synchronize attributes like visibility ?

Send a broadcast message to the peers, the peer receives it and changes the instance visibility ?

Or just to add an instance variable "visibility" on the object which will synchronize automatically, and add a global event (availble for the host and peers) like "if sprite visibility = true -> sprite ; set visible" ?

For those kind of actions I often just send a message to the peer.

send to peer xxxx, tag "setVisible" message = "no" (or yes)

Peer on received message "setVisible"

sub compare 2 values: Multiplayer.Message = "yes" , action set visible

sub compare 2 values: Multiplayer.Message = "no" , action set invisible

Thank you

What would be the benefits of this method compared to the other one (synchronized instance variable + peer event) I described ? More control on what's happening ?

Less synchronizing.

Depending on how you synchronize it, the state gets transferred between 10 and 30 times per second using synchronization methods, which would be a massive overhead on the bandwidth compared to just using a single transmitted command. Less overhead, less chance of lag.

Thank you for this essential information.