Replication¶

Properties (state) and actors (entities) are kept in sync from server to clients automatically when configured correctly.

Actor replication¶

AMyActor::AMyActor()
{
    bReplicates = true;
    bReplicateMovement = true;
    NetUpdateFrequency = 30.f;
    MinNetUpdateFrequency = 5.f;
}

The server decides which clients see the actor (relevancy).

Property replication¶

UPROPERTY(ReplicatedUsing=OnRep_Health)
float Health = 100.f;

UFUNCTION()
void OnRep_Health(float OldHealth);

void AMyActor::GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& Out) const
{
    Super::GetLifetimeReplicatedProps(Out);
    DOREPLIFETIME(AMyActor, Health);
    DOREPLIFETIME_CONDITION(AMyActor, Ammo, COND_OwnerOnly);
}

ReplicatedUsing calls OnRep_<Name> on clients whenever the value changes.
COND_OwnerOnly / COND_SkipOwner filter who receives the update.
COND_Custom lets you toggle replication dynamically.

Push Model¶

Default replication checks each property each tick. Push Model flips it: properties only replicate when explicitly marked dirty.

SetReplicatedProperty(Health, NewHealth);
MARK_PROPERTY_DIRTY_FROM_NAME(AMyActor, Health, this);

Enable in Project Settings → Networking → Use Network Push Model. Order-of-magnitude reduction in CPU for high-actor-count games.

Subobject replication¶

Replicate components on a replicated actor: set bReplicates = true on the component. For arrays of subobjects:

void AMyActor::PreReplication(IRepChangedPropertyTracker& Changer)
{
    Super::PreReplication(Changer);
    for (UMyComp* C : Components) AddReplicatedSubObject(C);
}

Network role¶

Role	Where
`ROLE_Authority`	The server's instance of the actor
`ROLE_AutonomousProxy`	The local owner's replicated copy (e.g. own pawn)
`ROLE_SimulatedProxy`	A replicated copy of an actor owned by someone else

Most authority checks: if (HasAuthority()) { ... }.

Tick groups + replication order¶

Replication happens in TG_LastDemotable. Avoid setting replicated state in client BeginPlay — set it server-side; the client will receive via OnRep.

Common pitfalls¶

Forgetting DOREPLIFETIME after declaring a Replicated property.
Calling RPCs on actors that haven't replicated yet (early in spawn).
Assuming BeginPlay order is consistent across server/client — order can differ.
Replicating large structs every frame — use Push Model or split into smaller properties.