Start Building

Lesson 6 gave patrol loops that yield when perception spikes. This lesson answers the next player question: “What does the guard do for the next ten seconds after they care?” You will add investigate, search, and cooldown behavior with clear exit rules, and stub a combat gate that your Lesson 1 fantasy allows—without turning the slice into a full shooter.

Course illustration - pixel console hardware study from Dribbble

Lesson objective

By the end of this lesson you will have:

  1. Blackboard-driven states beyond patrol: at minimum Investigate, Search, Engage (or Challenge), and Cooldown / Reset.
  2. A Behavior Tree priority stack where Engage beats Search, which beats Investigate, which beats Patrol.
  3. Timers or gameplay cues that force stand-down or escalation so guards do not infinite-loop on stale stimuli.

Step 1: Name the states honestly

Align names with what players see:

State Player-readable moment
Calm Normal patrol from Lesson 6
Suspicious Heard something; head turns, shorter moves
Investigating Moving toward StimulusLocation with caution
Searching Lost direct line; sweeping an area or last-known bubble
Engaged Confirmed threat: combat, alarm, or scripted flee (per Lesson 1)

If your fantasy forbids guns in v1, Engaged can mean detain or alarm call—the tree structure stays the same.

Step 2: Blackboard keys to add

Extend BB_Guard (or equivalent):

  • SearchPhaseTimer (float) – how long to sweep before giving up.
  • LastStateChangeTime (float) or TimeSinceLastSight – decay and fairness.
  • bLineOfSight (bool) – updated by perception or a cheap LOS check to avoid flapping.
  • CombatAllowed (bool) – off by default until you prove AI in a ring; matches Lesson 1 scope.

Pro tip: keep one writer for AlertLevel—perception delegates suggestions, the tree commits transitions to reduce race bugs.

Step 3: Suspicion and investigate

  1. On hearing without sight: set Suspicious, copy stimulus to a move target slightly offset (guards should not stand inside walls).
  2. Move To with slow speed and acceptance radius tuned for “peek corners,” not marathon sprints.
  3. If sight confirms while investigating, jump to Engaged (or your non-lethal equivalent).

Step 4: Search windows and cooldown

When LOS breaks after being Aware:

  1. Enter Search: pick N sample points around LastKnownLocation (simple grid or randomized offsets on NavMesh).
  2. Run SearchPhaseTimer; when it hits zero, ease back to Calm (optionally through Suspicious) with a Cooldown timer that blocks instant re-alert from the same noise shard.
  3. Log why the guard stood down in your debug HUD so playtesters trust the reset.

Common mistake: zero-second search—players never get tension. Aim for 3–8 seconds readable sweep on your greybox scale.

Step 5: Combat stub (scope-safe)

Engaged branch minimum viable slice:

  • Rotate toward player pawn or focus actor.
  • Optional play montage or AIMoveTo with lunge flag off—prove state, not DPS.
  • If player breaks LOS again, fall back to Search, not instant Calm, unless Lesson 1 says otherwise.

Hook damage or arrests in Lesson 9+ if your pillars demand it; here you prove state transitions.

Step 6: Debug and fairness pass

  1. Simulate three loops: noise only, sight only, noise then break LOS.
  2. Confirm perception cooldown does not hard-lock guards in Search forever—cap iterations.
  3. Two guards hearing the same clang should not path-stack; add assign investigation slot or stagger blacklist if needed.

Mini challenge

  1. Add one audio cue on state entry (soft sting for Suspicious, sharper for Engaged).
  2. Record time-to-calm after a failed search. Adjust timer until speedrunners cannot abuse a two-second hole.

Troubleshooting

Symptom Likely cause Fix
Insta-calms after combat Timer not gated by LOS history Require minimum Engage time
Ignores player in face Engage decorator missing Fix blackboard branch priority
Search circles one point Random offsets not on NavMesh Use Get Random Point in Navigable Radius
Stuck oscillating Calm/Aware Two writers on AlertLevel Single transition authority

Summary

  • State machines are promises to the player about duration and fairness.
  • Search needs spatial variety and a hard stop.
  • Combat can be non-lethal—keep the graph honest either way.

Further reading

FAQ

Do I need a full animation set for Engaged?
No. Turn-in-place + idle combat sells the state for a vertical slice.

Multiplayer later?
Replicate blackboard-driven states on the server; clients predict locomotion only when your net budget allows.

What if I want non-lethal takedowns?
Treat Engaged as grab attempt with a cooldown and player counter window—same tree, different tasks.

When guards commit to searches and recover with discipline, continue to Lesson 8: Stealth Tools and Gadgets for distractions and temporary disables that stress-test the state machine you wired here. Bookmark this lesson once Engaged never fires without a player-caused perception chain your QA notes can trace.