Tutorial 11 - LCMNav3D in the Gameplay Debugger

TL;DR: LCMNav3D ships an LCMNav3D category in the stock UE5 Gameplay Debugger. In PIE, press the standard Gameplay Debugger key (usually apostrophe '), select an agent → the category renders per-agent + plugin-wide state alongside Recast / BT / EQS / Perception. Zero project setup beyond the plugin being loaded.

What it shows

Plugin-wide block (always)

== LCMNav3D ==
  Manager: resolved
  Loaded chunks: 7
  NavLink registry: 3
  NavArea registry: 1
  NavSystem bridge: active

Per-agent block (when an actor is selected)

== Agent: BP_FlyingPawn_C_0 ==
  Pos: X=1234.5 Y=678.9 Z=500.0
  Speed: 624 cm/s
  Chunk: (0,0,0) full
  SweepPenalty: 0
  Perceived: 2 (closest: BP_Enemy_C_1)

How to toggle

1. In PIE, press the standard Gameplay Debugger key (usually apostrophe ' - check Project Settings → Engine → Gameplay Debugger if you've rebound it).
2. The Gameplay Debugger HUD appears at the top of the viewport.
3. Look for the LCMNav3D category - it should be enabled by default (state set to EnabledInGameAndSimulate at module init).
4. Click an actor in the level to select it as the debug target - per-agent block populates.

If the category isn't showing:

• Confirm you're in PIE (Gameplay Debugger only runs in PIE/Standalone, not the editor itself).
• Confirm the plugin is loaded (check Output Log for [LcmNavBridge] messages on map load).
• Confirm you're not in a Shipping/Test build (the category compiles out when WITH_GAMEPLAY_DEBUGGER=0).

What survives PIE → editor → PIE reloads

• CVars (debug toggles, chase tuning, OTel NDJSON, etc.) - persist across PIE sessions, reset on editor restart.
• Profile loader state (ULcmNavProfileSubsystem) - re-applied on each PIE init if the profile path is in your project's startup.
• Telemetry buffer - flushed at module shutdown; survives PIE-stop but not editor-close.
• NavLink + NavArea registry - populated at each actor's BeginPlay; PIE-stop clears via EndPlay.
• NavSystem bridge proxy - spawned per-world; new PIE session = new proxy.

The Gameplay Debugger category itself is always-on after module load - it doesn't lose its registration across PIE sessions because the category lives in the GameplayDebugger module's category map, not in the world.

Adding new fields (v2 design hook)

To extend the category in your project subclass:

#if WITH_GAMEPLAY_DEBUGGER
class FProjectGameplayDebuggerCategory_Apex: public FGameplayDebuggerCategory_LcmNav3D
{
public:
    virtual void CollectData(APlayerController* PC, AActor* DebugActor) override
    {
        Super::CollectData(PC, DebugActor);
        // Gather project-specific state here
    }
    virtual void DrawData(APlayerController* PC, FGameplayDebuggerCanvasContext& Canvas) override
    {
        Super::DrawData(PC, Canvas);
        Canvas.Printf(TEXT("  ProjectField: %s"), *MyProjectState);
    }
};
#endif

Register your subclass instead of the stock one in your project's module startup.

Performance

• CollectData is called once per tick per active category. Cost ≈ 10 µs (one GetActorOfClass + a few accessors + a perception query when an actor is selected).
• DrawData runs only when the HUD is visible. Cost ≈ negligible (text rendering).
• Shipping builds: zero cost (entire category compiles out via WITH_GAMEPLAY_DEBUGGER gate).

Related LCM Nav3D debug surfaces

• r.LcmNav.Debug.StateTreeOverlay - on-screen pawn state DrawDebugString
• r.LcmNav.Debug.CoverViz - cover-spot DrawDebugSphere overlay
• r.LcmNav.Debug.FlowFieldViz - flow-field arrow grid
• LcmNavStress.SpawnAgents <N> - stress-spawn helper for scale testing