09 — AI, Perception & Encounters Systems (Systems 80-88)
Category Purpose: These 9 systems form the enemy AI layer — base enemy character, patrol paths, alert state management, AI state machine, controller with behavior tree, blackboard definition, memory/last-known-location tracking, perception (sight/hearing/damage), and behavior variant selection. The AI_BaseAgentController runs behavior trees; all AI logic is data-driven via blackboard keys and behavior variants.
System Index
| # | System | Asset Type | Role |
|---|---|---|---|
| 80 | BP_EnemyBase |
Actor (Character) | Enemy base character; health, combat, patrol, death |
| 81 | BP_PatrolPath |
Actor | Patrol path spline; waypoints, wait times, loop |
| 82 | BPC_AlertSystem |
Component | AI alert states: Suspicious → Alerted → Combat |
| 83 | BPC_AIStateMachine |
Component | AI state machine: Patrol/Search/Combat/Flee |
| 84 | AI_BaseAgentController |
Controller | Base AI controller; behavior tree runner, perception init |
| 85 | BB_AgentBoard |
Blackboard | AI blackboard definition; all keys for enemy AI |
| 86 | BPC_AIMemorySystem |
Component | AI memory; last known locations, threat history |
| 87 | BPC_AIPerceptionSystem |
Component | AI perception; sight, hearing, damage sense |
| 88 | BPC_BehaviourVariantSelector |
Component | Behavior variant selection; weighted random from dataset |
AI Architecture
┌──────────────────────────────────────────────────────────────────┐
│ AI PIPELINE │
│ │
│ AI_BaseAgentController (AIController) │
│ │ Runs Behavior Tree defined in BB_AgentBoard │
│ │ Initializes perception system │
│ │ │
│ ├─► BPC_AIPerceptionSystem (senses) │
│ │ Sight: vision cone, distance, light level │
│ │ Hearing: sound events (gunshots, footsteps) │
│ │ Damage: takes damage → knows attacker location │
│ │ Team awareness: allies share detection │
│ │ │
│ ├─► BPC_AIMemorySystem (memory) │
│ │ Last known player location │
│ │ Threat history (who damaged me?) │
│ │ Investigation points (where to search) │
│ │ Forgets old data after configurable time │
│ │ │
│ ├─► BPC_AlertSystem (alert level) │
│ │ Suspicious → (investigate) → Alerted → (engage) │
│ │ → Combat → (player lost) → Search → (timeout) → Patrol │
│ │ Flee: low health threshold triggers retreat │
│ │ │
│ └─► BPC_AIStateMachine (behavior state) │
│ Patrol → Search → Combat → Flee │
│ State transitions driven by alert level + memory │
│ │
│ BPC_BehaviourVariantSelector │
│ │ Selects behavior variant at spawn: │
│ │ Attack patterns (aggressive, defensive, flanking) │
│ │ Patrol style (predictable, random, stationary) │
│ │ Aggression level (cautious, balanced, reckless) │
│ └─► Weighted random from DA_BehaviourVariant dataset │
│ │
│ BP_PatrolPath │
│ └─► Spline-based path with waypoints and wait times │
└──────────────────────────────────────────────────────────────────┘
82 — BPC_AlertSystem: Alert States
What It Does: Manages the enemy's alert progression — how aware they are of the player's presence. Drives behavior tree transitions and audio/visual feedback.
Alert Levels:
None: Unaware, patrolling normallySuspicious: Heard something, saw a glimpse — investigates last known locationAlerted: Confirmed player presence — moves to engageCombat: Actively fighting — shooting, chasing, flankingSearch: Lost sight of player — searches last known areaFlee: Health critical — retreats to safety
Escalation: Suspicion meter fills based on perception events. Partial sight = slow fill, full sight = fast fill, loud noise = burst fill. De-escalation: meter decays over time when no stimuli.
87 — BPC_AIPerceptionSystem: AI Senses
What It Does: Wraps UE5's AI Perception system with game-specific logic. Handles sight (vision cone + distance + light level), hearing (sound event radius + type priority), damage sense (instant alert on hit), and team awareness (nearby allies share detection).
Sight: Vision cone angle, max distance, peripheral vision penalty, light level modifier (harder to see in darkness), obstruction (line of sight trace)
Hearing: Gunshot > footstep > door creak. Louder sounds have larger radius. Running is louder than walking. Silenced weapons have reduced radius.
Team Awareness: If one enemy in a group detects the player, all nearby allies are alerted to the player's approximate position.
80-88: Remaining Systems
- 80 BP_EnemyBase: Character with health component, combat capability, patrol behavior, and death handling. Implements
I_Damageable. - 81 BP_PatrolPath: Spline component with waypoints. Each waypoint has wait time, look direction, and optional animation.
- 83 BPC_AIStateMachine: Discrete state machine: Patrol→Search→Combat→Flee. Transitions driven by blackboard values set by AlertSystem and PerceptionSystem.
- 84 AI_BaseAgentController: Custom AIController that runs the behavior tree, initializes perception, and manages the blackboard.
- 85 BB_AgentBoard: Blackboard Data Asset defining all keys: TargetActor, LastKnownLocation, AlertLevel, CurrentState, PatrolPath, HomeLocation, etc.
- 86 BPC_AIMemorySystem: Stores last known player location, threat sources, investigation points. Data decays over configurable time. Behavior tree queries memory to decide search patterns.
- 88 BPC_BehaviourVariantSelector: At spawn, selects a behavior variant from
DA_BehaviourVariantwith weighted random. Determines attack patterns, patrol style, and aggression. Creates enemy variety without separate classes.
Common Implementation Patterns in This Category
- Behavior Tree + Blackboard: All decision-making in behavior trees reading blackboard keys. Components write to blackboard; trees read and act.
- Alert Cascade: Suspicious → Alerted → Combat → Search → Patrol. Each state has different behavior tree branches.
- Memory with Decay: AI doesn't have infinite memory — last known locations are forgotten after time. Forces re-investigation.
- Perception Sharing: Team awareness prevents "why didn't his friend react?" — nearby allies share detection.
- Behavior Variants for Variety: Weighted random selection at spawn means enemies of the same class behave differently — no hardcoded enemy types.
Developer Reference v1.0 — 09 AI Systems. Companion to docs/blueprints/09-ai/ specs.