Game Code Mastery

AI System Usage Guide

6 min read

This guide provides detailed instructions on using the Combat AI Behavior System within the Advanced ARPG Combat framework in Unreal Engine 5. It covers key workflows for managing enemy AI behaviors, triggering combat actions, configuring patrol routes, and extending the system with custom AI behaviors, abilities, and configurations. The guide is designed for developers and designers to effectively utilize the system for creating dynamic enemy AI in Action RPGs.

Managing AI Behaviors

Control enemy AI behavior using the BP_BehaviorManagerComponent and SM_Humanoid_CombatBehavior.

  1. Select a BP_BaseEnemy in the level or spawned via BP_EnemySpawner.

  2. In the Details panel, locate BP_BehaviorManagerComponent and ensure it references a SM_Humanoid_CombatBehavior (set via BP_EnemyInfo).

  3. Adjust behavior properties in the referenced BP_EnemyInfo (e.g., BP_EnemyInfo_Humanoid):

    • Set Attack Distance for combat range.
    • Modify Enemy Aggression to control attack frequency.
    BP_EnemyInfo -> Behavior -> Set Attack Distance (Value: 500.0)

  4. Send events to trigger behavior changes:

    BP_BaseAIController -> UpdateTarget -> Set Blackboard Value As Object (Key: TargetActor, Value: Player) -> Send Event To State Machine (EventTag: Event.PlayerDetected)

Triggering Combat Actions

Execute AI combat abilities using Behavior Tree tasks and GA_EnemyAbility classes.

  1. Open the Behavior Tree (e.g., BT_ExampleAI) set in BP_EnemyInfo.

  2. Add a task node to execute an ability (e.g., GA_EnemyMeleeAttack):

    Behavior Tree -> Task: TryActivateAbilitiesByTag -> Set Blackboard Key (Key: AbilityTag, Value: Ability.MeleeAttack)

  3. Configure attack ranges in the Behavior Tree (e.g., close, medium, far) to select appropriate abilities.

  4. Ensure Default Ability Sets in BP_EnemyInfo includes the ability:

    BP_EnemyInfo -> Abilities -> Default Ability Sets -> Add (Class: GA_EnemyMeleeAttack)

Configuring Patrol Routes

Set up AI patrolling using BP_PatrolComponent and BP_PatrolPath.

  1. Place a BP_PatrolPath actor in the level.

  2. In the Details panel, adjust Patrol Points using the 3D widget to define the route.

  3. Select a BP_BaseEnemy and, in its BP_PatrolComponent, set Patrol Path to the BP_PatrolPath in the level.

  4. Optionally, if using BP_EnemySpawner set the Patrol Path to the BP_PatrolPath in the level.

  5. Configure patrol settings:

    BP_PatrolComponent -> Set bLoopPatrolPath (Value: True)

  6. If using with a behavior state manager, ensure to set the default behavior state to Behavior.Patrol in the EnemyInfoDataAsset to ensure the AI starts with Patrol behavior.

  7. Ensure the Behavior Tree includes a patrol task:

    Behavior Tree -> Task: Move To Patrol Point -> Set Blackboard Key (Key: PatrolPoint, Value: Next Patrol Point)

Managing Health and Ragdoll

Handle AI health bars and ragdoll effects during combat.

  1. On damage, trigger the health bar:

    BP_BaseEnemy -> OnDamageApplied -> ShowHealthBar

  2. On death, enable ragdoll:

    BP_BaseEnemy -> OnDamageApplied -> Is Health Zero? -> Branch (True) -> EnableRagdoll

  3. Configure PelvisBoneName in BP_BaseEnemy to match the AI’s skeletal mesh:

    BP_BaseEnemy -> Set PelvisBoneName (Value: pelvis)

Creating Custom AI Behaviors

Extend the system by creating a custom behavior state machine.

  1. Create new behavior tag in gameplay tag manager (e.g., Behavior.MyCustomBehavior)

  2. Open SM_Humanoid_CombatBehavior and modify the RunStateMachine event to add the new behavior to the switch statement and edit existing behaviors to configure when to transition into the new state.

  3. Optionally, Create a new Blueprint inheriting from SM_CombatBehavior (e.g., SM_MyCombatBehavior).

  4. Override RunStateMachine and UpdateBehavior to define custom behavior and transitions:

    UpdateBehavior -> Is State Equal To Any (State.Idle) -> Branch (True) -> Has Blackboard Value (Key: TargetActor) -> Branch (True) -> Enter State By Tag (StateTag: State.Chase)

  5. Adjust behavior properties (e.g., Attack Distance, Enemy Aggression) in the Details panel.

  6. In BP_EnemyInfo, set Behavior Classes to include SM_MyCombatBehavior.

  7. Update the Behavior Tree to support new states:

    Behavior Tree -> Task: Custom Action -> Set Blackboard Key (Key: BehaviorTag, Value: Behavior.MyCustomAction)

Creating Custom Enemy Abilities

Develop new AI abilities for unique combat behaviors.

  1. Create a new Blueprint inheriting from the appropriate enemy ability class.
    1. For completely custom enemy abilities inherit from GA_EnemyAbility (e.g., GA_MyEnemyAbility)
    2. For Attack Abilities inherit from GA_EnemyMeleeAttack (e.g., GA_MyEnemyAttack)
    3. For Dodge a Dodge Ability inherit from GA_EnemyDodge (e.g., GA_MyEnemyDodge)

NOTE:

There are several default enemy abilities for you to inherit from and configure without the need to write any code. Check AdvancedARPGCombat > MeleeCombatSystem > Blueprints > Abilities > AI to see what default abilities you can inherit your custom ability from.

  1. Set ability properties (e.g., Attack Montage, Gameplay Tags) in the Details panel.

  2. If using a default included enemy action ability such as Attack or Dodge, simply set the desired animation montage.

  3. Configure optional Ability Montage properties

    1. Set AbilityEndType to either Automatic or Manual depending on use case. If manual the ability will need to be ended by adding the AN_EndAbility anim notify to the ability montage.
    2. Configure EndTimeMultiplier value for automatic ability ending (e.g., 0.8)
    3. Set Montage PlayRate to desired value (e.g., 1.0)
    4. Set InTimeToStartMontageAt to desired value to change when the montage starts
    5. Configure StartSectionName to desired value to change the default start montage section

  4. For completely custom enemy abilities, Override ActivateAbility to define behavior:

    ActivateAbility -> Play Montage (Montage: AM_MyAttack) -> Apply Gameplay Effect (Effect: GE_Damage)

  5. Add the ability to Default Ability Sets in BP_EnemyInfo:

    BP_EnemyInfo -> Abilities -> Default Ability Sets -> Add (Class: GA_MyEnemyAbility)

  6. Update the Behavior Tree to trigger the ability:

    Behavior Tree -> Task: Perform Ability -> Set Blackboard Key (Key: AbilityTag, Value: Ability.MyCustomAttack)

Creating Custom Enemy AI

Create a new enemy type with custom configurations.

  1. Create a new Blueprint inheriting from BP_BaseEnemy (e.g., BP_MyEnemy).
  2. Set AI Controller Class to BP_BaseAIController in the Details panel.
  3. Create a new BP_EnemyInfo (e.g., BP_MyEnemyInfo):
    • Set AI Pawn Class to BP_MyEnemy.
    • Assign a custom Anim Class and Combat Style.
    • Add custom abilities and behaviors (e.g., SM_MyCombatBehavior, GA_MyEnemyAbility).
    • Add custom behavior tree or select included behavior tree
    • Configure hostile tags to ensure the enemy can detect hostiles
  4. Configure BP_MyEnemy to use BP_MyEnemyInfo: 
    BP_MyEnemy -> Event BeginPlay -> SetEnemyInfoRef (EnemyInfo: BP_MyEnemyInfo)
  5. Place BP_MyEnemy in the level or use BP_EnemySpawner with BP_MyEnemyInfo.

Notes

  • Use BP_EnemyInfo for all AI configurations to leverage async loading and simplify setup.
  • Combine Behavior Tree tasks and SM_Humanoid_CombatBehavior properties for fine-tuned AI behavior.
  • Test custom behaviors with demo assets to understand default interactions before scaling complexity.
  • Ensure Gameplay Tags are unique to avoid conflicts between AI and player systems.

Troubleshooting

  • AI Not Transitioning States:
    • Verify SM_Humanoid_CombatBehavior is set in BP_EnemyInfo and referenced by BP_BehaviorManagerComponent.
    • Ensure UpdateBehavior in SM_Behavior processes valid Gameplay Tags or Blackboard values.
    • Check Behavior Tree tasks are setting correct Blackboard keys.
  • Abilities Not Executing:
    • Confirm Default Ability Sets in BP_EnemyInfo includes the ability class.
    • Verify Combat Style in BP_EnemyInfo matches the ability’s requirements.
    • Ensure ActivateAbility in the ability class is correctly configured.
  • Patrol Not Working:
    • Check BP_PatrolPath is assigned to BP_PatrolComponent and Patrol Points are defined.
    • Ensure a Nav Mesh Bounds Volume covers the patrol area.
  • Health Bar or Ragdoll Issues:
    • Verify OnDamageApplied calls ShowHealthBar and EnableRagdoll in BP_BaseEnemy.
    • Confirm PelvisBoneName matches the AI’s skeletal mesh.

Best Practices

  • Workflows:
    • Start with demo BP_EnemyInfo and SM_Humanoid_CombatBehavior to test default behaviors before customizing.
    • Use hierarchical Gameplay Tags (e.g., Behavior.Combat.Attack, Enemy.Hostile.Player) for clarity.
    • Regularly test AI in-game to validate Behavior Tree and FSM interactions.
  • Pitfalls to Avoid:
    • Don’t skip setting HostileTags in BP_EnemyInfo or BP_BehaviorManagerComponent to ensure proper targeting.
    • Don’t forget to add Behavior Tree to BP_EnemyInfo
    • Don’t hard-reference assets; use BP_EnemyInfo for async loading.

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