Interaction: Traces + Blueprint Interface

What/Why: Simple, scalable interaction using a trace and a Blueprint Interface. Keeps props reusable and player logic thin.

Prereqs

• Collision channel for interactables (optional); or use Object Types (WorldDynamic) and tags
• Input: IA_Interact (Bool) bound in IMC_Gameplay

Steps

1. Create the interface

• Create BPI_Interactable with functions:
  • Interact(Instigator: Actor) — called on server
  • Highlight(bEnable: bool) — client-side feedback
  • GetPrompt() -> Text — UI hint

2. Build an Interaction Component (Actor Component)

• BP_InteractionTraceComponent (attach to Pawn):
  • Variables: TraceDistance (float = 300), TraceRadius (float = 8), bDrawDebug (bool)
  • Function FindBestInteractable():
    • LineTrace or SphereTrace from camera forward; ignore owner; filter by Does Implement Interface BPI_Interactable
    • Track CurrentTarget; if changed, call Highlight on new/old
  • Function TryInteract():
    • If CurrentTarget valid → run Server_Interact(CurrentTarget) RPC on owning client

3. Wire input to interaction

• In Pawn/Controller: bind IA_Interact (Triggered) → call InteractionTraceComponent.TryInteract()
• Call FindBestInteractable() on a low-frequency timer (e.g., 10–20 Hz) or when look direction changes (advanced)

4. Implement the prop side

• Any Actor can implement BPI_Interactable:
  • Interact → perform action (open door, pick up) on server
  • Highlight → enable outline/indicator locally
  • GetPrompt → return a short text for UI

Data

• Optional DA_InteractConfig for trace distance, prompt style, outline color
• Use Gameplay Tags on interactables for categories (Interact.Type.Door, Item, Terminal)

Networking

• Interact call is server-authoritative: Owning client → Server_Interact(Target) → validate → execute
• Highlight stays client-side; don’t replicate unless needed
• Replicate state changes (doors open, items gone) via normal replicated vars/Multicast

Performance

• Avoid per-tick heavy traces; use a timer at ~0.05–0.1s or event-driven updates
• Prefer LineTraceForObjects over complex channels; keep collision simple
• Cull highlight FX in distance; avoid material parameter spam every frame

Testing

• Add a debug print of GetPrompt() when a target is available
• Toggle bDrawDebug to see traces; verify highlight swaps when looking around
• Press Interact once; action triggers once on server (no client-only side effects)

Suggested prompts

• “UE 5.6 Blueprints only. Create BPI_Interactable with Interact(Instigator), Highlight(bool), and GetPrompt(). Show a player component that traces and calls these functions.”
• “What timer rate is reasonable for interaction traces and how do I avoid spamming highlight?”
• “Show how to make Interact server-authoritative via RPC from the owning client.”
• “Provide a quick checklist for collision and trace filters when interactions don’t detect.”

Prompts for this example

• “Given my BP_InteractionTraceComponent, write the nodes to do a line trace from the camera and pick the nearest actor that implements BPI_Interactable.”
• “Show the RPC wiring for Server_Interact(Target) so Interact runs only on the server.”