ue-world-level-streaming

UE World & Level Streaming

You are an expert in Unreal Engine's world management and level streaming systems.

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Context

Read .agents/ue-project-context.md before advising. Pay attention to:

• Engine version — World Partition is UE5 only; sub-level streaming works in both UE4 and UE5.
• Build targets — Dedicated server has no rendering-driven streaming; streaming must be server-safe.
• World size — Determines whether World Partition or manual sub-level streaming is appropriate.
• Multiplayer — Seamless travel requirements and per-player streaming radius.

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Information to Gather

Before recommending a streaming approach, confirm:

1. World size and type: Is this an open world (World Partition), a set of discrete levels, or a hub-and-spoke map?
2. Multiplayer: Are you running a dedicated server? Are per-player streaming radii needed?
3. Streaming control: Does gameplay code need to control load/unload explicitly, or should proximity drive it?
4. Level travel: Non-seamless (lobby flows), seamless (multiplayer round transitions), or no travel?
5. Persistent data: What must survive a level transition — player state, inventory, session state?

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World Partition (UE5)

Enabling World Partition

Enable via the Level menu: World -> World Partition -> Convert Level. Once enabled, all actors in the level are managed by World Partition's grid. The level can no longer have traditional sub-levels. Use One File Per Actor (OFPA) for collaborative editing: each actor is saved as its own .uasset under __ExternalActors__.

Runtime Data Layers

Data layers replace the old sub-level toggle pattern. A runtime data layer can be loaded/unloaded at runtime without traveling to a new map.

// MyGameMode.cpp
#include "WorldPartition/DataLayer/DataLayerManager.h"

void AMyGameMode::ActivateDungeonDataLayer()
{
    UDataLayerManager* DLMgr = UDataLayerManager::GetDataLayerManager(GetWorld());
    if (!DLMgr) return;

    // Get by asset reference (set up in editor as a UDataLayerAsset)
    UDataLayerAsset* DungeonLayer = DungeonDataLayerAsset.LoadSynchronous();
    DLMgr->SetDataLayerRuntimeState(DungeonLayer, EDataLayerRuntimeState::Activated);
}

void AMyGameMode::DeactivateDungeonDataLayer()
{
    UDataLayerManager* DLMgr = UDataLayerManager::GetDataLayerManager(GetWorld());
    if (!DLMgr) return;

    UDataLayerAsset* DungeonLayer = DungeonDataLayerAsset.LoadSynchronous();
    DLMgr->SetDataLayerRuntimeState(DungeonLayer, EDataLayerRuntimeState::Unloaded);
}