Interactor Component Trace

What You'll Learn

• Precise (line) vs Loose (box) tracing and when to use each
• The full set of tunable trace properties
• How to trace from a custom origin (e.g. a weapon muzzle) instead of the owner's eyes

Core Concepts

UMounteaInteractorComponentTrace detects interactables via a periodic line or box trace from the owner's eye location (or a custom transform). It's the natural fit for camera-aim / crosshair interaction - no sibling collision shape required, since it traces from the actor itself.

UMounteaInteractorComponentTrace : public UMounteaInteractorComponentBase

Key Properties

Property	Type	Default	Notes
TraceType	EMounteaTraceType	ETT_Loose	ETT_Precise = thin line trace; ETT_Loose = forgiving box sweep
TraceRange	float (cm)	250	Maximum interaction distance
TraceShapeHalfSize	float (cm)	5	Box half-extent, only used when TraceType = Loose
TraceInterval	float (s)	0.05	How often the trace re-fires
bUseCustomStartTransform	bool	false	Enable + set CustomTraceTransform to trace from somewhere other than the owner's eye location

UENUM(BlueprintType)
enum class EMounteaTraceType : uint8
{
    ETT_Precise,  // Line Trace - requires precision, better for small objects
    ETT_Loose,    // Box Trace - forgiving, better for large objects
};

Custom trace origin

Enable bUseCustomStartTransform and set CustomTraceTransform to trace from a weapon muzzle, a turret barrel, or any socket other than the owner's camera/eye location - useful when the interaction origin shouldn't follow the player's look direction.

API

Trace->EnableTracing();    // starts the periodic timer
Trace->DisableTracing();   // stops the timer, releases all detected interactables, clears hits
Trace->PauseTracing();     // pauses the timer WITHOUT clearing currently detected interactables
Trace->ResumeTracing();
bool CanTrace = Trace->CanTrace();

PauseTracing/ResumeTracing differ from Disable/Enable specifically in whether the current detected set survives - pause for a brief UI overlay, disable for a real deactivation.

Each tunable property has a paired getter/setter (GetTraceType/SetTraceType, GetTraceRange/SetTraceRange, etc.), with setters routing through Server, Unreliable RPCs.

Detection Flow

Each trace tick (ProcessTrace) runs either ProcessTrace_Precise or ProcessTrace_Loose depending on TraceType, collects hit results, and diffs them against DetectedSet via LastTraceHits - new hits call AddDetected(), stale hits call RemoveDetected(), which in turn triggers RefreshFocus() on the base.

State-Change Behaviour

ProcessStateChanged() starts/stops the periodic trace timer on active/inactive state transitions, so a Suppressed or Disabled Trace interactor performs zero trace queries per frame rather than tracing and discarding results.

See Interactor System for the base component's two-tier focus model.