Skip to content

Building Entity Types

This page describes the public data types used for Building Entities, ownership, save data, and world rebuilding.

Type Relationships

EBuildingOwnerType
└── FBuildingOwnerId
    └── FBuildingEntity
        └── FUpdateBuildingEntityInfo
            └── FEntitySnapTree

FUpdateBuildingEntityIdInfo
├── EntityId
├── WorldTransform
└── FEntitySnapTree

EBuildingOwnerType

EBuildingOwnerType represents the type of a building owner.

Enum Value Description
None No valid owner.
Player A player.
Faction A faction or team.
NPC An NPC.
System The game system or another system-level object.

FBuildingOwnerId

FBuildingOwnerId represents building ownership using an owner type and a stable string ID.

This structure does not depend on a Player Controller, Player State, Pawn, or Actor instance.

Fields

Field Type Default Description
Type EBuildingOwnerType None The owner type.
Id FString Empty The stable identifier of the owner.

A valid owner ID must satisfy:

Type != None
Id is not empty

Member Functions

Function Description
IsValid Checks whether the owner type and ID are valid.
IsPlayer Checks whether the owner is a player.
None Creates an empty owner ID.
Player Creates a player owner ID.
Faction Creates a faction owner ID.
operator== Compares two owner IDs.

Projects usually provide owner IDs through IBuildingOwnerProvider.

For interface details, see Project Interfaces.

Warning

Do not use Actor names, object addresses, temporary array indexes, or runtime Controller IDs as persistent owner IDs.

FBuildingEntity

FBuildingEntity represents the persistent data of a placed building.

Fields

Field Type Default Description
EntityId int32 INDEX_NONE The unique identifier of the Building Entity.
ChunkId int32 0 The Chunk to which the building belongs at runtime.
WorldTransform FTransform Identity The building's world transform.
BuildableAssetId FPrimaryAssetId Invalid The ID of the building configuration asset.
OwnerId FBuildingOwnerId None The building owner.
EntityData FBuildingEntityData Default The persistent state of the building.

EntityId

EntityId is used for:

  • Querying buildings
  • Moving or removing buildings
  • Network synchronization
  • Snap Tree references
  • Save restoration

An invalid ID uses:

INDEX_NONE

RebuildAll preserves existing EntityId values and sets the next ID to the highest existing ID plus one.

ChunkId

ChunkId is runtime data.

When the world is rebuilt, Chunks are recreated and assigned according to WorldTransform. Therefore, ChunkId should not be used as a persistent relationship.

WorldTransform

WorldTransform stores:

Component Description
Location World-space location.
Rotation World-space rotation.
Scale World-space scale.

BuildableAssetId

BuildableAssetId references the UBuildingDataAsset used to create the Entity.

When restoring a building, the system uses this ID to locate the corresponding building data asset.

OwnerId

OwnerId can be used for:

  • Building permissions
  • Save ownership
  • Faction checks
  • Building statistics
  • Resource refunds

EntityData

EntityData stores additional building state, such as:

  • Gameplay Tags
  • Attributes
  • Health or durability
  • Project-specific extension data

FUpdateBuildingEntityInfo

FUpdateBuildingEntityInfo combines a complete Entity with its Snap Tree.

Field Type Description
Entity FBuildingEntity The complete Building Entity.
SnapTree FEntitySnapTree The building's snapping relationships.

It is primarily used by:

API Purpose
CollectSaveRecords Collects the current building records.
RebuildAll Rebuilds the building world from saved records. 
CollectSaveRecords
→ Save TArray<FUpdateBuildingEntityInfo>
→ Read the save data
→ RebuildAll

Note

The Snap Tree represents snapping relationships and is not used for structural support evaluation.

FUpdateBuildingEntityIdInfo

FUpdateBuildingEntityIdInfo is a lightweight update structure.

Field Type Default Description
EntityId int32 INDEX_NONE The target Entity ID.
WorldTransform FTransform Identity The updated world transform.
SnapTree FEntitySnapTree Default The updated snapping relationships.

This type is used for internal update operations that do not need to transfer the complete EntityData.

Standard projects usually do not need to create this structure manually.

Type Usage

Type Purpose Complete Entity Snap Tree
FBuildingOwnerId Building ownership No No
FBuildingEntity Individual Building Entity Yes No
FUpdateBuildingEntityInfo Save data and world rebuilding Yes Yes
FUpdateBuildingEntityIdInfo Lightweight updates No Yes

Save Rules

Save Do Not Save
EntityId Actor pointers
WorldTransform HISM Component pointers
BuildableAssetId HISM Instance Indexes
OwnerId Render Chunk Actor pointers
EntityData Runtime component mappings
SnapTree Client preview state

During rebuilding:

Preserve EntityId
→ Reassign Chunks according to WorldTransform
→ Rebuild runtime representations
→ Next Entity Id = Highest existing Entity Id + 1
Functionality API
Query a single Entity UBuildingWorldSubsystem::TryFindEntity
Get all Entities UBuildingWorldSubsystem::GetAllEntity
Collect save records UBuildingWorldSubsystem::CollectSaveRecords
Rebuild the building world UBuildingWorldSubsystem::RebuildAll
Get the owner ID IBuildingOwnerProvider::GetBuildingOwnerId