09 — Blueprint Integration¶

The Fuzzy Logic Component¶

UFuzzyLogicComponent is available in the Fuzzy Logic group and can be added to any actor.

Property	Value
System Asset	A shared `UFuzzySystemAsset`; takes priority
Inline System	A local system, used when no asset is assigned

Both are writable from Blueprint. The component caches the compiled system and notices when you point it at a different System Asset, so swapping behaviour profiles at runtime just works. Editing the Inline System struct in place is the one change it cannot see — call Mark System Dirty after that.

Feeding Inputs¶

Node	Behavior
Set Input	Writes a single value; returns `false` if the name isn't among the inputs
Set Inputs	Writes a `Map<Name,float>`; returns the count of names found
Get Input	Returns the supplied or default value
Clear Inputs	Forgets supplied values and returns the system to `Default Value`

Supplied values persist between evaluations. Only update what has changed.

Evaluation¶

Node	Result
Evaluate	The full `FFuzzyInferenceResult`
Evaluate Output	A single number by output name
Evaluate Single Output	The number of the sole output
Get Last Result	The previous result without a new computation

The Evaluate nodes are deliberately not Pure: inference does real work, and a Pure node could silently repeat it for every pin reader.

Typical Actor Pattern¶

Event Tick or a timer
  → Set Input (Distance)
  → Set Input (Health)
  → Evaluate Output (Aggression)
  → apply to speed, transition weight, or action selection

Use Evaluate Output when you need one number. Use Evaluate when you also need the degrees, activations, or diagnostics — then read a crisp value out of the result's Outputs map with a standard Find node.

For a large number of agents, you don't have to evaluate every frame. Evaluate on a timer, on a significant input change, or spread agents across frames.

Inspection¶

Node	Purpose
Is System Valid	Whether the system compiled without errors
Validate System	The full list of diagnostics
Get Input Names / Get Output Names	Names in declaration order
Get Last Output Surface	The exact surface from the last evaluation
Mark System Dirty	Reset the cache after editing the `Inline System` struct in place

Get Last Output Surface returns false for an unknown output name and before the first Evaluate, so a plot can never show a curve the system never produced. A flat zero surface is a real answer — "no rule fired" — and comes back as success.

Shared Systems For Many Agents¶

A component carries its own copy of the system it evaluates. That is the right trade for a handful of actors and wrong for a crowd: a hundred components pointing at one asset hold a hundred copies of it.

UFuzzyLogicSubsystem compiles each asset once and shares the result. There is nothing to set up — Unreal creates it with the game instance. Reach it with Get Game Instance Subsystem, class Fuzzy Logic.

Node	Purpose
Evaluate Asset	Full `FFuzzyInferenceResult` for an asset's system
Evaluate Asset Output	A single number by output name
Prepare Asset	Compiles ahead of time, e.g. on a loading screen
Validate Asset	Compiles if needed and returns the diagnostics
Invalidate Asset / Invalidate All	Drops a cached compilation after changing a system at runtime
Is Asset Prepared	Whether an asset is already compiled and waiting
Get Cached System Count	How many systems are currently cached

Event Tick or a timer
  → Get Game Instance Subsystem (Fuzzy Logic)
  → Make Map (Distance → 450, Health → 72)
  → Evaluate Asset Output (Asset = BehaviorAsset, Output Variable Name = "Aggression")

The difference from the component is that nothing is remembered between calls: pass every input the system needs each time, because there is no per-actor state to hold them. Variables you leave out fall back to their Default Value. There is no Get Last Result either.

Use the component for a few actors, per-actor systems, or when you plot a decision. Use the subsystem when many agents share one behaviour asset. Both give identical numbers — the same engine decides.

Editor note: saving a change to a cached asset drops its entry, so a Play-In-Editor session always runs the version you just saved.

Static Library¶

UFuzzyLogicStatics is convenient for one-off operations without a component:

Evaluate Fuzzy System;
Validate Fuzzy System;
Parse Fuzzy Rule and Fuzzy Rule To String;
Save/Load Fuzzy System To Json;
Evaluate Fuzzy Set;
Make Fuzzy Term Key;
Describe Fuzzy Set;
Fuzzy Diagnostic To String.

For repeated evaluation, use the component: it caches the compiled system.

Result Structure¶

Break FFuzzyInferenceResult to get crisp outputs, input degrees, set and rule activations, and diagnostics. All six fields are Blueprint-readable.

The struct's C++ helpers (GetOutput, GetSingleOutput, HasErrors) are not Blueprint nodes. From Blueprint:

read a crisp value with Find on the Outputs map;
check bSuccess before applying the result of a system that may come from user-supplied data;
to distinguish errors from warnings, loop over Diagnostics and compare Severity, or call Validate System on the component.