World Partition¶
The UE 5.x large-world streaming system. Replaces the legacy "level streaming" pattern for open worlds.
How it works¶
A WP map auto-partitions actors into a 2D grid of cells (default 25,600 cm). At runtime, cells stream in/out based on the player's Streaming Source.
Each actor in a WP map is stored as One File Per Actor (OFPA) — see OFPA — making the map itself a tiny file pointing to the actor files.
Enabling¶
World Settings → World Partition → Enable World Partition. New projects from "Open World" template have this on.
Streaming sources¶
By default, the player pawn is a streaming source. Add custom sources:
Examples:
- Drone cameras (stream where the drone is, not the player)
- Cinematic cameras (stream around active camera during cinematic)
- AI commanders (stream their patrol area)
Editor workflow¶
| Action | How |
|---|---|
| Edit a region | Loaded Regions panel — load cells you're working on |
| Force-load all | "Load All" (slow, only for small maps) |
| HLOD generation | World Partition window → Generate HLOD |
| Visualize cells | Top-down view + cell overlay |
HLOD layers¶
HLOD Layer data assets define proxy strategies per actor type:
- Instancing — combine many copies into HISM
- Simplified Mesh — auto-generate proxy mesh at distance
- Disabled — don't show at distance
World Partition + PCG¶
PCG can generate per-cell at runtime — see PCG → World Partition.
Streaming policy¶
| Policy | When |
|---|---|
| Standard | Most cases |
| Blocking | Synchronous loads on critical cells (hitches but safe) |
| High Priority | Important cells preempt others |
Data layers¶
Data Layers toggle subsets of actors on/off — Day/Night layers, Mission-specific actors, etc. See Data Layers.
Performance budgets¶
- ~5–10 ms per cell streaming load on typical SSD.
- HLOD generation can take hours on large worlds — run on CI.
- Memory: aim for ≤8 streaming cells loaded at any time on consoles.
Gotchas¶
- Level Blueprint references in WP are awkward — prefer World Subsystems.
- Some legacy plugins assume monolithic levels — verify WP compatibility before adopting.
- Editor preview vs runtime cell behavior can differ — use Simulate World Partition in PIE.