Custom senses#

Anything you can express as how sure am I that this target is there? can be a sense: thermal, radar, magnetism, a motion sensor, psychic awareness. A custom sense joins the same pipeline as the built-in ones: it combines with them, drives the seven states, feeds threat, and shows in the Visualizer.

In Blueprint#

1. Make the class. Content Browser › right-click › Blueprint Class › All Classes › search Sense Unit › pick it as the parent. Name it BP_Sense_Thermal.

You can also parent to a built-in sense (Smell Sense, Vision Sense...) to change its own settings in Class Defaults: that is how the Senses page's bloodhound gets a stronger nose (Smell).

2. Get Sense ID. Override it and return a unique name, Thermal. It's what Get Sense Contributions and the Visualizer show.

3. Evaluate. Override it: it is called for one target at a time, each time the sense updates.

Fill in Out Result (a Perception Sense Result): drag from the Return Node's Out Result pin and pick Make Perception Sense Result.

Evaluate (Context, Profile, Target)
  Distance   = Vector Distance (Context › Owner Location, Context › Target Location)
  Branch: Distance > 3000 → return (Out Result left empty)
  Heat       = the target's heat (a tag, a component, a variable: your game)
  Confidence = (1 − Distance ÷ 3000) × Heat
  Out Result: Is Active = Confidence > 0.1, Confidence, Estimated Location = Target Location,
              Location Accuracy = 0.8, Sense ID = Thermal

4. Add it to the profile's Sense Classes (up to 8 senses). Optionally weight it in Sense Weights and set how often it runs in Sense Intervals.

Its class defaults: the Sense Contract#

A sense made directly from Sense Unit declares how it behaves in its Class Defaults, Sense Contract:

A custom sense isn't in the profile's Loss settings, so these are its loss rules; its belief fades at the normal rate.

Vision, Hearing, Smell, Touch, Vibration, Damage, Pain and Echolocation answer these in C++ and ignore the Sense Contract. On a Blueprint child of Vision Sense, setting them changes nothing; use the profile's settings instead.

What a Blueprint sense can't do#

A custom sense's Stimulus on On AI Suspect and On AI Detect reads Unknown: tell it apart with Get Sense Contributions.

In C++#

Make a child of USenseUnit and override what you need:

UCLASS(BlueprintType, Blueprintable, DisplayName = "Radar Sense")
class MYGAME_API USenseUnit_Radar : public USenseUnit
{
    GENERATED_BODY()
public:
    virtual FName GetSenseID_Implementation() const override { return FName("Radar"); }
    virtual float GetDefaultInterval()        const override { return 0.5f; }
    virtual float GetMaxSensingRange()        const override { return 8000.f; }
    virtual float GetLossGraceTime()          const override { return 1.0f; }
    virtual bool  AllowsDirectLostCut()       const override { return true; }

    virtual void Evaluate_Implementation(const FPerceptionContext& Context,
        const UPerceptionProfile* Profile, const AActor* Target,
        FPerceptionSenseResult& OutResult) override;
};

Each update, in this order:

The APS Core never casts to a particular sense: everything sense-specific lives in the sense class, so adding one changes nothing else. Other overrides:

The stimulus bus#

A broadcast channel for your own signals: Emit Stimulus (callable from any Blueprint, no target needed) with an APSStimulus Event, and every sense that listens for a matching tag prefix receives it.

Delivery runs cheapest first: radius, detail tier, team, then the wall trace.

Who listens: only Vibration Sense among the built-in senses (Stimulus.Vibration, and Stimulus.Sound.Explosion: blasts shake the ground), and it turns them into beliefs about the place. Hearing doesn't listen to the bus: it hears only Emit Sound and Emit Sound at Location (Hearing). Your own C++ sense subscribes like this:

virtual TArray<FName> GetStimulusTags() const override
{
    return { FName(TEXT("Stimulus.Custom.Psychic")) };
}

virtual void OnStimulusReceived(const FAPSStimulusEvent& Event) override
{
    PendingPsychicEvents.Add(Event);   // use it in the next PreTick or Evaluate
}

A Blueprint sense can list tags in Subscribed Stimulus Tags, but receiving is C++ only, so nothing happens when one arrives. For a Blueprint reaction to your own signal, call Set Target Confidence or Report Location Belief on the AI you want to affect.

Ideas#