Conditional Property Replication

This page assumes you already have working knowledge of Unreal Engine’s replication system.

Read the Multiplayer page for information about Unreal’s replication system and special cases for Satisfactory.

Conditional Property Replication was introduced in the 1.0 release and is a Coffee Stain custom extension of Unreal’s normal conditional actor replication system. It replaced the Replication Detail Actor system used in previous versions.

The purpose of the system is to reduce the amount of data being sent to multiplayer clients. Example use cases are for replicating the inventories or state of a building only when clients have the building’s interface open.

Replicating Inventories

To use the system to replicate an inventory component, follow these steps from Arch. The steps assume you are replicating an FGBuildable’s inventory component.

Create UFGInventoryComponent as a class default object in your class:

AFGBuildableManufacturer::AFGBuildableManufacturer()
{
    mInputInventory = CreateDefaultSubobject<UFGInventoryComponent>(TEXT("InputInventory"));
}

Make sure your property (in this case mInputInventory) is NOT marked as Replicated OR SaveGame. Both flags do not do anything useful and only create additional overhead in runtime:
```
UPROPERTY()
UFGInventoryComponent* mInputInventory;
```
In BeginPlay, if HasAuthority, call UFGInventoryComponent::SetReplicationRelevancyOwner and pass the buildable as argument:
```
void AFGBuildableManufacturer::BeginPlay()
{
    Super::BeginPlay();
    if (HasAuthority())
    {
        mInputInventory->SetReplicationRelevancyOwner(this);
    }
}
```
- If you skip this step, your inventory will ALWAYS be replicated if the owner building is replicated. However, if you follow it, the inventory will ONLY be replicated to the client if it has the buildable UI open.
Now just use the same inventory on both server and client. No need for any kind of hacks with inventory object swapping or waiting for inventories. The inventory is always available now on the client as an object, but the contents are only replicated when needed.

Replicating Additional Data for UIs

To replicate additional (non-inventory) data for UIs, follow these steps from Arch. The steps assume you are replicating data for an FGBuildable with an interact UI.

Make a UPROPERTY marked with meta = (FGReplicated) or meta = (FGReplicatedUsing = OnRep_XXX) (in case you need a RepNotify function for your property):

UPROPERTY(meta = (FGReplicated))
float mCurrentManufacturingProgress;

UPROPERTY(meta = (FGReplicatedUsing = OnRep_ArbitrarySlotSizes))
TArray<int32> mArbitrarySlotSizes;

Override GetConditionalReplicatedProps, and add your property there using macros (depending on whenever it was marked as FGReplicated or FGReplicatedUsing):

void AFGBuildableManufacturer::GetConditionalReplicatedProps(TArray<FFGCondReplicatedProperty>& outProps) const
{
    Super::GetConditionalReplicatedProps(outProps);
    FG_DOREPCONDITIONAL(ThisClass, mCurrentManufacturingProgress);
}

void UFGInventoryComponent::GetConditionalReplicatedProps(TArray<FFGCondReplicatedProperty>& outProps) const
{
  Super::GetConditionalReplicatedProps(outProps);
  FG_DOREPCONDITIONAL_WITH_NOTIFY(ThisClass, mArbitrarySlotSizes, OnRep_ArbitrarySlotSizes);
}

That’s it! Now your property will only be replicated when the buildable UI is open.