World Streaming authoring

This chapter covers editor-side authoring: world definition, entity membership, the partition view, collaboration shards, and migrating existing levels.

World definition: WorldConfig + `.wsworld`

A partitioned world has two parts:

WorldConfig entity on the level root with WorldStreamingConfigComponent.
Sibling .wsworld descriptor listing bake aggregation sources and optional chunk / server-shard knobs.

WorldStreamingConfigComponent is bake-time data: the processor reads it and strips it, so it never reaches the runtime Root Spawnable and has no component-panel editing. It is normally written by the WorldStreaming_Level template, the Migration Tool, or EditorWorldStreamingRequestBus AuthorWorld* events.

Field	Description
`WorldGuid` / `m_worldGuid`	World identity for multiplayer handshake and bake-aggregation validation
`CellIdSalt` / `m_cellIdSalt`	CellId hash salt; regenerate when grid layout (cell size / origin) changes
`Grids` / `m_grids`	Grid level list
`Layers` / `m_layers`	Content Layer descriptors
`HlodLayers` / `m_hlodLayers`	HLOD layer descriptors

Grid levels (`WorldStreamingGridDesc`)

Field	Default	Description
`m_gridLevel`	0	Level number; with multiple grids, lower = finer
`m_cellSize`	128 m	Cell edge length
`m_defaultLoadRadius` / `m_defaultActivateRadius`	256 / 128 m	Fallbacks when a streaming source gives no explicit radii
`m_verticalPartitioning` + `m_cellSizeZ`	off	Vertical (Z) partitioned grid
`m_singleTierActivation`	off	Activate on spawn, skipping the Loaded warmup tier
`m_use2DDistance`	off	Vertically partitioned grid streams by XY-plane distance
`m_streamingPriority`	0	Priority bias under budget pressure (ordering only)
`m_gridOriginD`	(0,0,0)	Grid origin offset; changing it re-partitions the world

Grid change severity

Changing grids raises interactive warnings:

Severity	Meaning
None / TuningOnly	Safe tuning (radii, priority)
Additive	Additive layout change
FullRepartition	Full re-partition—confirm in the modal, regenerate `m_cellIdSalt`, and rebake everything

Entity membership rules

Assignment priority:

Member with IsSpatiallyLoaded = false → AlwaysLoaded cell.
Explicit m_runtimeGridLevel (not inherit).
Otherwise pivot position on the default (finest) grid.
Opt-in m_autoGridLevelFromBounds: pick the finest grid that can contain the world AABB.

Ordinary entities need no Member component. Cross-cell hard references are diagnosed by default; enable m_patchCrossCellHardRefs plus DependentLoad to record alias repair entries.

`WorldStreamingMemberComponent`

Field	Default	Description
`IsSpatiallyLoaded` / `m_isSpatiallyLoaded`	`true`	`false` = AlwaysLoaded (still gated by Content Layers)
`RuntimeGridLevel` / `m_runtimeGridLevel`	`0xFF` (inherit)	Explicit target grid
`LayerId` / `m_layerId`	`0`	Owning Content Layer
`BundleGroupId` / `m_bundleGroupId`	`0`	Strong-reference co-load group
`DependentLoadTargets`	empty	Target entities’ cells must be at least Loaded before this cell activates
`ExcludeFromHlod` / `m_excludeFromHlod`	`false`	Static meshes never enter HLOD proxy geometry
`SoftReferenceTargets`	empty	Soft cross-cell refs; does not pull the target cell

Transform hierarchy clustering (opt-in)

m_clusterTransformHierarchy (default off) keeps Transform parent/child trees in the same cell as the root. Enabling it changes cross-cell layout—rebake after changing.

Partition view (`Tools > World Streaming`)

Typical panel capabilities:

Area	Actions
Overview	World status, grid / layer summary
Focus loading	Load a radius around the camera for editing without activating the whole world
Loaded Regions	Persistent editor regions of interest; never enter the runtime Manifest
Content Layers	Toggle / inspect layer authoring state
Bake	Bake World Streaming, Bake Region, Bake GPU Octahedral Impostors
Shards	Save Dirty Cell Shards, AutoShard, Focus Edit Cell Shard
Migration	Migration Tool. for existing levels

Unloaded-cell proxies in the viewport are session-only and never saved or baked.

Collaboration shards (editor)

Editor shards split cell content into independent Prefabs for multi-user editing. This is not the same as server shards.

Granularity	Control	Notes
Primary shard (default)	—	One shard Prefab per cell
AutoShard	“Auto-create shards on first content”	Creates a shard when content first lands in an empty cell
Sub-shards	“Max entities per sub-shard” (`0` = off)	Split into `_sN` by entity-count cap
Per-actor sidecars	“Per-actor sidecars” (requires AutoShard)	`_a<key>` one file per entity
Orphan sidecar cleanup	“Delete pruned sidecar files” (default off)	Default only unregisters; on = source-control-aware delete

Sub-shards / sidecars conflict with independent multi-source cells unless both migration m_allowMultiSourceCells and bake key MergeMultiSourceCells are on.

Use Save Dirty Cell Shards before bake or handoff. Scripted focus: FocusEditCellShard / ClearEditCellShardFocus on EditorWorldStreamingRequestBus.

Migration Tool

For levels that predate World Streaming:

Open Tools → World Streaming → Migration Tool..
Choose grids / layers / salt options the dialog exposes.
Commit; the tool writes WorldConfig + .wsworld and rewrites Prefabs as needed.

Alternatively automate with AuthorWorldBegin → AuthorWorldAddGrid / AuthorWorldAddHlodLayer / AuthorWorldSetShardSize → AuthorWorldCommit (see Scripting).

Next steps

Baking: produce .wsmanifest and cell Spawnables.
Content Layers / HLOD: declare advanced world features.
Reference: full field tables.