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Things in the replication{} block (see AOCPawn) gets replicated using the conditions noted in the block. I don't know, look at AOCPawn, look at the documentation, it's fairly straight-forward. Make note of the repnotify keywork, which fires an event when a thing is replicated.

Variable replication is the typical way of running something or copying a variable to every client (the other way being calling a Client function on every PlayerController on the Server).

Kismet Replication

Kismet runs on the server unless you mark an event as "client-side only", in which case it runs on the client. If the Kismet needs to communicate between server and client somehow, and the nodes we want to use don't do that (or don't do it in the way we want; e.g. Matinees will run on the server and replicate the actor changes to every client, but replicating every changed property every frame or so can end up being pretty expensive for non-gameplay-relevant actors), there are some tools to fix that. See /wiki/spaces/CHIV/pages/622626.