Interface: implement and call Blueprint interface function

SETUP: Create a Blueprint Interface asset (BPI_Interactable) with a function 'Interact'. IMPLEMENT: In the actor BP, go to Class Settings → Interfaces → Add → BPI_Interactable. Then implement the 'Interact' event that appears in the event graph. CALL: Get actor reference → 'Does Implement Interface(BPI_Interactable)' → Branch → True → 'Interact (Message)' node (the interface call). Key: Interface calls are 'Message' type nodes. Use 'Does Implement Interface' before calling to avoid crashes on actors that don't implement it.

Blueprint claims to implement an interface but didn't add the function

Why: You added an Interface to this Blueprint's class settings, but you never actually implemented '{fn}'. Other code calling this interface will get a no-op when it expects real behavior. Fix: In My Blueprint panel → Interfaces section → find '{fn}' → click the wrench icon → 'Implement Function'. UE5 adds an empty function stub for you. Fill in the body with whatever this interface method should do.

Interactable interface system with line trace from camera

Pattern: BPI_Interactable interface with Interact(APawn* Caller) and GetInteractText(). Player Tick: GetPlayerCameraManager → GetCameraLocation/Rotation → LineTraceSingle(CamLoc, CamLoc + Forward*InteractDistance) → BreakHitResult → HitActor → DoesImplementInterface(BPI_Interactable) → True: show UI prompt, store as FocusedActor. Interact input → call Interact(Self) on FocusedActor.

Implements

Says a Blueprint provides a given Interface's functions. Other Blueprints can call those functions via the interface reference.

Interface

A contract a Blueprint can implement, exposing a set of functions other code can call without knowing the class. Used for decoupled comms.

string

string

Physics Body

A SceneComponent with simulate-physics enabled. Driven by forces, gravity, collisions instead of explicit transforms.

SetInputModeGameAndUI — set input for both game and UI

AddToViewport — display a widget on screen

Line trace raycast for interaction system

Pattern: Input trigger → LineTraceSingle(CameraLocation, CameraLocation + ForwardVector * Distance, Visibility, false, MakeArray(Self), None) → Branch(ReturnValue) → True: BreakHitResult → HitActor → CastTo InteractableInterface → call Interact. End pin is world POSITION not direction. Use DrawDebugType ForOneFrame during dev.