Call Function Only on Client, or Only on Server

[Denz_Noviembre]

Trying to understand some more basic concepts, to get me going on the multiplayer. I have watched videos and read documentation, but they don’t properly cover this kind of understanding.

1. If I want to do a function Only on client, or Only on server, does the below screenshot achieve that?
   

   

2. If I have a reliable RPC for owning client, is it guaranteed to execute only on the owning client, no matter where it’s called, and will it execute only once? So for example I have 1 listen server and 2 clients, will that RPC execute only once when I call it, and only on the owning client? If no, how can I achieve that?
   Same question for the server RPC.

3. A more specific question, say, I want to change the player movement speed, but do it in a way that player doesn’t feel lag (Doesn’t have to wait for server validation). Is the below screenshot the correct way to do it?
   

   

[KingOfTheEnd374]

1. Yes, these functions would be called on Server and Client as you named them. You should also keep in mind, that the Client Function will be called for each client by each client. For example, I have 2 clients and 1 server client (listen server). Here is a sketch of what actors would call what functions. Green calls are simulated on Client 1, blue calls on Client 2, and red calls on Server.
   

   
   
   If you want ClientFunction to only be executed on the client it is in, use IsLocallyControlled:
   Is Locally Controlled | Unreal Engine Documentation

2. No, RPC for the owning client can ONLY be called from the Server as a client-owned actor. Here is a table for what can be called from where.
   

   
   
   This is from UE4 Network Compendium by Cedric ‘eXi’ Neukirchen

It will be executed as many times as you call it. I would need more info to help what you exactly want to achieve here. Generally, if some logic needs to call a client RPC once, just check that on the server (use do once or boolean logic).

3. It is almost correct. If you want the client to predict movement change, the original ClientEvent doesn’t need to be RPC, but just a regular event called from that client(for example, pressing the Sprint key). It would technically work as is, but as it is now, it gives off an assumption that it would be called from the server, which would mean, you aren’t predicting the move speed like you stated, but just updating it from the server.

Here are some good reads on networking:

Multiplayer Network Compendium | An Unreal Engine Blog by Cedric Neukirchen

Unreal Engine Multiplayer Tips and Tricks

[Denz_Noviembre]

Thanks for the response. Before I commit to turning the rest of my code into multiplayer, could you tell me if I did the below screenshots right? So that I know that I understood everything correctly.

The goal currently is to replicate sprinting, in a way that character doesn’t feel lag.
I tested and this works, but working doesn’t necessarily mean that I did it correctly.

P.S. I know that for this simple speed change it would be better to not use tick, but I’m gonna use much more complicated calculations on client to set target speed, and this will make things much easier, and the branch check ensures it will fire the server RPC only when necessary.

[KingOfTheEnd374]

Your code should work and it seems right if you must use tick. If you are planning on using a listen server (one client is the server), then you should have a HasAuthority check before that RPC (and connect false/remote to RPC), because the Server Client will already set its speed on the server and there would be no need for that RPC.

[Rev0verDrive]

Multiplayer logic for sprinting is as follows.

This logic flow for the most part mirrors the crouch and jump logic found in character movement component (CMC).

Input → determine if you can do action → Do Action → RPC Server

Server → determine if you can do action → Do Action

Threads:

I create sprint movementm how replicate it to multiplayer?

The lag is caused by your client waiting on the server to make the change and replicate that to you. You have to apply the speed change to the client and then call the server to make the change. DO NOT MULTICAST CMC Movement Changes. Input → Can I change Speed! [TRUE] → Change speed on client → RPC Server Server → Can I change Speed [TRUE] → Change speed on server This is the simplest it gets. [image]

What is the best way to change player movement speed (multiplayer)

[image] [image] Here’s a simple Blueprint version of it using Rep_Notify enumerator (CharMoveSpeed). When you Set/Change a Rep_Notify variables value its OnRep Function is executed. I take advantage of this on the client to force calling the function by changing the value locally. I then call the server to run the flow logic to make its own determination.

How dynamic your character is determines the complexity of movement speed change logic.