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Networking/Replication - Epic Wiki

# Networking/Replication

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# Contents

# Overview

Unreal Engine has been designed with networking in mind since Unreal Engine 1.
This includes:

  • Remote procedure calls (RPC).
  • Replication of variables, including structs & dynamic arrays.
  • Dedicated server support.
  • VOIP

# Creating a server

# Listen

A listen server includes the host as a local player.
To launch a listen server, use the command line:
<mygame.exe> ?listen -game

# Dedicated

A dedicated server does not include the host as a local player.
Renderering, audio, and anything else that isn't required is disabled to use a minimal footprint both in memory and cpu.

To launch a dedicated server, use the command line:
<mygame.exe> -server

Games that are ready to ship with cooked data will also include a standalone executable <mygameserver.exe>.
These are fully optimized for multiple instances per machine.

To launch a dedicated server using <mygameserver.exe>, use the command line:
<mygameserver.exe>

# Joining a server

To join a server at a specified IP address as a client, use the command line:
<mygame.exe> -game

To join a server via the in-game console, use the command:
open

# Play In Editor Support

The editor includes built in support for networked games.

This is incredibly handy for quickly testing multiplayer games on a single host machine.

PIE Options

PIE Advanced Settings

# Blueprint support

Blueprints fully support replication, including replication notifications.
Replication notifications are handy if you want a client to do something when a variable updates.
eg. Play a particle effect if their health increases.

Blueprint Replication

Blueprint On Rep

# C++ examples

# Sync character health to all clients

# YourCharacter.h

UPROPERTY(Replicated)
float Health;

# YourCharacter.cpp

#include "UnrealNetwork.h" // ... void AYourCharacter::GetLifetimeReplicatedProps(TArray< FLifetimeProperty > & OutLifetimeProps) const { Super::GetLifetimeReplicatedProps(OutLifetimeProps);

// Replicate to everyone
DOREPLIFETIME(AYourCharacter, Health);

}

The DOREPLIFETIME macro is defined in UnrealNetwork.h, so make sure you #include it in your .cpp file. Your project will need a dependency on the "Engine" module in its Build.cs file to find the header, but most projects will have this dependency already.

# Command from client to server

# YourPlayerController.h

bool bSomeBool;

void SetSomeBool(bool bNewSomeBool);

UFUNCTION(reliable, server, WithValidation)
void ServerSetSomeBool(bool bNewSomeBool);
virtual void ServerSetSomeBool\_Implementation(bool bNewSomeBool);
virtual bool ServerSetSomeBool\_Validate(bool bNewSomeBool);

As of UE 4.15 the compile system adds the implementation and validation definitions for you. Making the code for the header as follows

bool bSomeBool;

void SetSomeBool(bool bNewSomeBool);

UFUNCTION(reliable, server, WithValidation)
void ServerSetSomeBool(bool bNewSomeBool);

You'll still need everything in the cpp file though!

# YourPlayerController.cpp

void AYourPlayerController::SetSomeBool(bool bNewSomeBool) { // Change the value of the bSomeBool property bSomeBool = bNewSomeBool;

// If this next check succeeds, we are \*not\* the authority, meaning we are a network client.
// In this case we also want to call the server function to tell it to change the bSomeBool property as well.
if (Role < ROLE\_Authority)
{
    ServerSetSomeBool(bNewSomeBool);
}

}

bool AYourPlayerController::ServerSetSomeBool_Validate(bool bNewSomeBool) { return true; }

void AYourPlayerController::ServerSetSomeBool_Implementation(bool bNewSomeBool) { // This function is only called on the server (where Role == ROLE_Authority), called over the network by clients. // We need to call SetSomeBool() to actually change the value of the bool now! // Inside that function, Role == ROLE_Authority, so it won't try to call ServerSetSomeBool() again. SetSomeBool(bNewSomeBool); }

Kris

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