Unreal Engine Hack & Slash Tutorial [2024] Series | Part 21 | Enemy AI Melee Combat

Main Ideas / Concepts Covered

• Building the first melee AI enemy in Unreal Engine:
  • Enemies strafe around the player and then switch into melee attack behavior.
• Implementing a full melee attack pipeline:
  • AI decides it can/should attack (behavior tree + blackboard/state checks).
  • AI plays an attack montage and uses AnimNotifies to trigger weapon hit detection.
  • Weapon hit detection applies damage only under the correct conditions.
• Handling common AI-control issues:
  • Prevent attacks from being interrupted or repeatedly triggered while already attacking.
  • Ensure Blackboard keys and “saved attack” flags are cleared/reset properly after attack animations.
  • Tune timer/loop intervals so behavior tree state changes don’t conflict.

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Methodology / Instruction-Style Steps

1) Start/Finish the Enemy “Melee Combat” Behavior

• Ensure the enemy already:
  • Chases + strafes.
  • Switches positions when the player is too far, or when search logic finds a new spot.
• Visually confirm attack timing:
  • Enemies light up when an attack is about to occur.
  • Attack indicators help confirm one enemy lights up while attacks are incoming.

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2) Add Attack State Gating: can attack

• Use a custom event/function approach and a state-based check for gameplay consistency.
• Create a function such as can attack that returns whether the enemy is allowed to start an attack.
• Intended state exclusions (examples):
  • Enemy cannot attack if in any of these states:
    • Attacking
    • Dodging
    • Dead
    • Disabled
    • (and possibly additional movement conditions like “flying” / “falling,” depending on implementation)

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3) Implement Attack Playback Using Montages (Index-Based)

• Add an attack montage array (e.g., Attack montages array).
• Implement logic such as perform attack:
  • Accepts an attack index
  • Validates the index
  • If valid:
    • Set enemy state to Attacking
    • Play the selected attack montage
• Compile and confirm the montage plays when the attack is triggered.

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4) Add Weapon Collision / Hit Detection via AnimNotify

• Add a weapon static mesh to the enemy and attach it to a weapon socket.
• Create a function like Draw Weapon Collision (copied/adapted from player logic), taking inputs such as:
  • radius
  • start/end range (trace sweep parameters)
  • damage type class
  • target cast type (e.g., cast hit actors to the player BP)
• Behavior:
  • Detect actors in the collision/trace area
  • For each hit actor:
    • Cast to the player character
    • Check player state (e.g., not dead)
    • Apply damage (set damage amount, apply selected damage type)

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5) Trigger Collision During the Animation

• In the enemy’s attack montage:
  • Add an AnimNotify at the right moment (e.g., “Draw Weapon Collision”).
  • In the notify event, call the weapon collision function.
• Expose and tune notify collision parameters (example values mentioned):
  • ready ≈ ~50
  • end ≈ ~150–250 (tuned experimentally)

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6) Integrate Attack Decision into Behavior Tree Using Timers

• Use a timer approach instead of a full fight director.
• Create a loop timer in the AI controller/event graph:
  • Uses Random Float in Range (roughly 3–8 seconds initially, later tuned)
  • On completion, set a blackboard value to an attack/fight state (e.g., BehaviorStates = Fight)
• In the Behavior Tree:
  • Give attack higher priority than tasks like strafing.
  • Use abort settings so lower-priority branches stop when attack state becomes active.

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7) Fix Repeated/Overridden Attacks (Critical Bug Handling)

Observed problems

• Attacks could trigger too many times or cancel too quickly because behavior tree reevaluations override state before montage completion.
• Delay-based task completion didn’t reliably prevent re-entry.

Fixes applied

• Add a “save attack” boolean key:
  • Blackboard boolean like B_SaveAttack
• Logic intent:
  • When attack conditions occur, store intent so it won’t be lost briefly due to re-evaluations.
  • Attack task should only run when:
    • Not already attacking
    • B_SaveAttack is set (or relevant conditions are true)
• Clear/reset:
  • Clear B_SaveAttack
  • Reset/clear the main state key after the montage ends
• Result:
  • Stabilizes behavior so the attack montage plays fully before another attack begins.

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8) Implement Melee Combo Variation + Chance-Based Attacks

• Add an additional melee combo montage:
  • e.g., enemy combo attack 1
  • Include its own reset state notify/section
• Add a BT decorator for chance:
  • Decorator checks:
    • random integer in range 0..100
    • If <= chance, allow the combo task
• Add cooldown after playing combo (example: 5 seconds mentioned).
• Adjust structure:
  • Switch to a Selector instead of a Sequence to avoid deterministic “always combo then again” behavior (as noted in the video).

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9) Improve Facing / Targeting During Attacks

• Reduce chaotic spinning by controlling focus:
  • Use Set Focus during the attack moment
  • Use Clear Focus at an appropriate time (often around end of animation timing)

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10) Add Attack Indicators (Readability / Telegraphing)

• Add an overlay material signaling system:
  • Custom event Start Attack:
    • Set overlay material on enemy mesh
  • Custom event End Attack:
    • Clear overlay (set material to none)
• Wire indicator events to attack task:
  • Start indicator when approaching/entering attack state
  • End indicator after attack montage begins/after a delay
• Result:
  • Players get clearer anticipation that an enemy is about to attack.

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11) Prevent Taking Damage During Invulnerability Windows (i-frame Logic)

• Fix damage application so damage only occurs when i-frames are not enabled:
  • In damage code, add a branch:
    • If iFrames enabled == true → do not take damage
    • Else → allow damage
• Result:
  • The player no longer takes hits in scenarios where invulnerability should apply.

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12) Final Tuning and Stress Test

• Stress test by spawning multiple enemies simultaneously.
• Adjust tuning values:
  • Attack timer random ranges
  • Behavior tree wait intervals during strafing
  • Movement acceptance radius / approach radius (mentioned as being tuned toward ~50–600 depending on observed behavior)
• Notes:
  • Combat can work but may become chaotic with many enemies colliding/spreading.
• Suggested future improvements:
  • Check whether the target is in the air and back away or adjust positioning
  • Improve collision avoidance between enemies

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Speakers / Sources Featured

• Primary speaker (creator/instructor): “guys welcome back…” / tutorial narrator (no name given in subtitles)
• Video source: Unreal Engine hack & slash tutorial series, Part 21: Enemy AI Melee Combat (2024) (referenced by the video title)