Build at scale. Keep every piece.

ABuildingPiece is the abstract base class for every wall, floor, foundation, door and window.

Editor-only helpers bAutoCenterMeshX/Y/Z can center mesh bounds on PieceRoot. For multi-leg pieces, bCheckPieceRootClearance and GroundClearanceCheckPoints define the exact support points to test.

UBuildingComponent::TryConfirmPlacement checks whether the piece class implements IInteractable.

Demolition is player-driven through TryDemolishPiece. It bypasses health and is gated by CanDemolishPiece.

Damage uses ABuildingPiece::ApplyDamage, clamps CurrentHealth, broadcasts OnHealthChanged, and destroys the piece at zero. The engine’s TakeDamage path is supported, so UGameplayStatics::ApplyDamage works for Actor-backed pieces.

When only a trace hit is available, call UBuildingCombatLibrary::ApplyDamageToHitResult. It resolves whether the hit belongs to an Actor or an instance. For a game-wide destruction event covering both representations, bind to UBuildingRegistrySubsystem::OnAnyPieceDestroyed.

An FBuildingSnapPoint is a compatible attachment location on a piece.

Snap-point helpers bAutoCenterX/Y/Z keep points aligned to changing mesh bounds. Native tags ship below Building.Piece.* for foundation, floor, wall, doorframe, windowframe, roof, door, window and stair, with wood and stone examples. Extend them with native tags or through Project Settings > GameplayTags.

UBuildingPieceRules is an optional data asset for required-parent rules such as “a door requires a doorframe”. Assign it to the hologram’s PlacementRules. Omitted piece types remain unrestricted.

ABuildingHologram mirrors the selected PieceClass: mesh, offset, snap radius, occupancy and clearance settings. It traces up to TraceDistance every frame, or on the configured PlacementUpdateInterval, finds compatible snap points, checks blocking and reports through IsPlacementValid().

Assign ValidMaterial and InvalidMaterial for visual feedback. The class can be extended with particles, audio and UI. The current attachment is exposed through GetMatchedParentPiece(), GetMatchedParentPieceID(), IsMatchedParentInstance() and GetMatchedSnapPointIndex().

UBuildingComponent drives placement and demolition from your own input bindings. It does not depend on Enhanced Input.

CurrentDemolishTarget and CurrentDemolishTargetID expose the current target. Feedback delegates include OnPiecePlaced, OnPieceDemolished and OnDemolishTargetChanged. Instance highlighting uses SetPieceInstanceCustomDataValue.

UBuildingRegistrySubsystem is created automatically once per world. It is the source of truth for both Actors and instances.

FBuildingPieceData Data;
if (Registry->GetPieceData(SomePieceID, Data))
{
    // Data.CurrentHealth, Data.PieceType, Data.Transform...
}

Use HasPiece and GetAllRegisteredPieceIDs for reads. DestroyInstancePiece is the complete removal path for an instance, including its snap data and ISM entry. Delegates OnPieceRegistered, OnPieceUnregistered and OnAnyPieceDestroyed expose world-level lifecycle events.

The world is split into a grid of chunks, 5000 units per cell by default. Each active chunk owns one ISM component per distinct mesh used inside it. Chunks are created only when pieces are placed.

UBuildingChunkSubsystem resolves AddPieceInstance, RemovePieceInstance, UpdatePieceInstanceTransform and SetPieceInstanceCustomDataValue, including transparent movement across chunk boundaries. To drive material highlights, configure NumInstanceCustomDataFloats before placing pieces and read the values with a Per Instance Custom Data material node.

Building traces use Visibility by default.

Failures are reported to LogAukkeBuildingSystem. Use log LogAukkeBuildingSystem Verbose in the console for detailed placement information.

All debug rendering is editor-only and removed from Shipping builds.

Check that a mesh is assigned, verify whether the piece type requires a parent, inspect ground clearance, then read the log message explaining the rejected validation.

Its Blueprint was probably renamed or deleted after the save was written. The missing piece is logged and the rest of the save continues loading.

The automatic occupancy box is slightly smaller than mesh bounds. If collision bounds still extend past the visible mesh, disable bAutoOccupancyCheckExtent and configure OccupancyCheckBox manually.

Move DemolishTraceChannel away from Visibility and use a dedicated project collision channel.

• No networking yet. Placement, demolition and saving are local and non-authoritative. Multiplayer requires an authority layer.
• Windows only for now. The restriction is currently declared in the .uplugin; the C++ has not been validated on other platforms.
• No structural integrity system yet. Removing a support does not automatically collapse descendants. ParentPieceID already stores the attachment chain for a future layer.
• No resource costs or permissions by default. Implement them through CanConfirmPlacement and CanDemolishPiece.