Interactor Component Mouse

What You'll Learn

• When Mouse detection fits your project better than Overlap or Trace
• What the owner actor needs for this component to function
• Why the trace runs client-side, not server-side

Core Concepts

UMounteaInteractorComponentMouse detects interactables via a world-space ray cast from the current mouse cursor position, using APlayerController::DeprojectMousePositionToWorld to build the trace ray. It's built for top-down and isometric games where interaction is mouse-driven rather than camera-forward.

UMounteaInteractorComponentMouse : public UMounteaInteractorComponentBase

Owner requirement

The owner must be, or be possessed by, a Pawn with an associated APlayerController - GetOwnerPlayerController() resolves this via possession, and the component is inert without one (no controller means no cursor to deproject).

Key Properties

Property	Type	Default	Notes
MouseTraceRange	float (cm)	5000	Maximum world distance for the ray cast
MouseTraceInterval	float (s)	0.05	How frequently the mouse position is re-evaluated

API

Mouse->EnableMouseTracing();     // starts the cursor trace timer
Mouse->DisableMouseTracing();    // stops it, clears the detected set
bool CanTrace = Mouse->CanMouseTrace();

Client-Side Tracing, Server-Reported

DeprojectMousePositionToWorld needs a local viewport - only the client that owns the pawn actually has cursor/viewport data. So the trace itself always runs on the locally-controlled client (or the listen-server host acting as its own client), and the result is reported to the server via ReportHitActors_Server (an Unreliable Server RPC) so the server's own copy of DetectedSet/ActionList stays in sync - the server has no independent way to derive "what's under this specific client's mouse cursor" the way it can re-simulate Overlap or Trace detection identically on both sides.

Unreliable is intentional

ReportHitActors_Server fires at roughly MouseTraceInterval Hz - a dropped RPC is superseded by the next trace tick moments later, so Reliable delivery would only add latency without improving correctness.

State-Change Behaviour

ProcessStateChanged() starts/stops the mouse-trace timer on active/inactive transitions, matching the Trace component's pattern.

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