3D Horror - Systems (Make game skill)

Part of the make-game skill. The skill links here when your agent needs the detail.

The dread machinery on top of 3d-horror.md: the tension-driven atmosphere controller, the stalker AI, procedural audio, interactables, and the escape objective chain.

Atmosphere controller (tension in, dread out)

One Node3D in the level reads GameManager.tension_level and escalates three channels. It auto-discovers OmniLights from a sibling “Lights” node and creates 4 roaming AudioStreamPlayer3D emitters (Ambient bus, max distance 20).

Flickering lights

Per-frame chance 0.005 * (1.0 + tension) per light. A flicker is a tween of 2-5 random off/on cycles (off 0.02-0.08s at energy 0-0.3, on 0.02-0.1s at 50-100%), then restore. Random durations - regular flicker reads as a broken script, not a broken light.

Positional ambient sounds

Every 15-45s (interval shrinks to half at max tension), one emitter teleports to a random point around the player (x/z +-15, y 0-5 - behind walls, above the ceiling) and plays from a pool that GROWS with tension:

base: door close, pipe stress, wind vent
tension > 0.3: + creature whisper
tension > 0.5: + distant scream
tension > 0.7: + creature growl

Random volume -12..-4 dB and pitch 0.7-1.3 so nothing repeats exactly.

Tension events

Every 30s at base, down to ~12s at max tension, pick one of FIVE: 0 = flicker all lights, 1 = audio stinger + tension +0.05, 2 = brief darkness, 3 = extra ambient sound, 4 = NOTHING. The nothing case is deliberate - a scare that never comes after buildup is the horror. Brief darkness: tween all lights to energy 0.05 over 0.5s, hold a random 0.5-2s, restore over 0.3s, tension +0.08. Save original energies first.

Stalker AI

A solid-black unshaded capsule (CapsuleMesh r 0.2 h 2.2, albedo 0.01 - reads as a silhouette in any lighting). Mesh and collision built at runtime, no assets. Core mechanic: it only moves when you are NOT looking.

func _process_showing(delta: float) -> void:
	look_at(Vector3(player.global_position.x, global_position.y, player.global_position.z))
	var to_me := (global_position - player.global_position).normalized()
	var player_fwd := -player.global_transform.basis.z.normalized()
	var angle := rad_to_deg(acos(clampf(player_fwd.dot(to_me), -1.0, 1.0)))
	if angle < 20.0:
		# player looking directly: freeze and stare back
		stare_timer += delta
		if stare_timer >= stare_time:      # 2.0s of being watched
			_disappear()
	else:
		stare_timer = 0.0
		var dir := (player.global_position - global_position).normalized()
		dir.y = 0.0
		velocity = dir * approach_speed    # 1.5 m/s
		move_and_slide()
		if global_position.distance_to(player.global_position) < catch_distance:  # 1.5m
			AudioManager.play_sfx(ProceduralAudio.get_creature_screech(), 0.0)
			GameManager.set_state(GameManager.GameState.GAME_OVER)

Pacing rules (tuned, keep them):

First appearance at 15s - the player needs time to find the flashlight.
Reappear interval starts 18s, shrinks 15% per appearance, floor 8s: reappear_interval = maxf(reappear_interval * 0.85, 8.0).
Spawn selection: from a hand-placed spawn-point list, pick the FARTHEST point that is between 6m and 18m from the player. Under 6m is unfair - no time to react.
On appear: whisper from its own 3D emitter + low-pitched stinger (pitch 0.5-0.8) + tension +0.1.
Fully idle while GameManager.is_reading_note or state != PLAYING - notes are safe rooms.
After stare_time of being watched it vanishes (visible = false) and the wait timer restarts. Player-facing check is a dot-product cone of 20 degrees, not a raycast - cheap and good enough.

Procedural audio

ProceduralAudio is a static class generating every sound from math into cached AudioStreamWAVs - zero audio files; swap in recordings later without touching call sites. Catalog: footsteps (4 variations), door open/close/locked, ambient drone (detuned 40Hz sines, looping), tension hit (sub boom + metallic ring), pickup chime, creature whisper/growl/screech, heartbeat, distant scream, water drip, machinery hum, wind vent, fluorescent buzz, pipe stress, radio static. Generation pattern all sounds follow (16-bit, 22050 Hz):

static func _generate_example() -> void:
	var num_samples := int(duration * SAMPLE_RATE)
	var samples := PackedByteArray()
	samples.resize(num_samples * 2)
	for s in num_samples:
		var t := float(s) / SAMPLE_RATE
		var envelope := exp(-t * 3.0)
		var value := sin(t * 440.0 * TAU) * envelope * 0.3
		var sample := clampi(int(value * 16000), -32768, 32767)
		samples[s * 2] = sample & 0xFF
		samples[s * 2 + 1] = (sample >> 8) & 0xFF
	_stream = AudioStreamWAV.new()
	_stream.format = AudioStreamWAV.FORMAT_16_BITS
	_stream.mix_rate = SAMPLE_RATE
	_stream.data = samples
	# looping sounds: loop_mode = LOOP_FORWARD, loop_begin = 0, loop_end = num_samples

Recipes that matter: creature sounds = low fundamentals (30Hz growl) + inharmonic partials; whispers/screams = filtered noise; drones = slightly detuned sine pairs (beating); always exponential envelopes.

Interactables

Same duck-typed interface as 3d-fps: interact(player) + get_interaction_prompt() -> String, found by the InteractionRay (mask 4).

HorrorDoor

Node3D rotating on Y, hinge at the parent origin (mesh offset (0.5, 1.4, 0)), lerp rotation.y toward target at open_speed. Opens away from the player (approach-side check). Horror-specific exports:

required_key: locked until GameManager.has_item(key); unlocking consumes the key. Locked interaction plays a rattle - +-2 degree shake tween + locked sound. Prompt: “Locked” / “Unlock” / “Open” / “Close”.
auto_close_delay: door closes itself behind the player (room traps).
creepy_auto_open: opens by itself ONCE after a delay - cheapest scare in the kit.

InteractableItem

RigidBody3D with freeze = true, bob + rotate idle (randomized phase), per-type runtime mesh + OmniLight3D glow:

Type	Effect	Visual
KEY	`add_item(item_id)`	gold box, warm glow
FLASHLIGHT	`player.pickup_flashlight()`	gray cylinder, amber glow
NOTE	`open_note(id, text)` - NOT consumed	paper-white flat box
BATTERY	battery +30 (cap 100)	dark blue box, blue glow

Everything except notes queue_free()s on pickup.

EscapeZone

Area3D (mask 1) at the exit with a green OmniLight beacon. On player enter: with the exit key -> set_state(ESCAPED); without it -> open a note (“The door is chained from the outside. I need a key.”) - the rejection delivers story instead of a dead trigger.

Objective chain

The loop is explore -> find -> unlock -> escape:

Spawn in entry area, find flashlight.
Main hall, Note 1 hints at the storage key.
Side corridor -> office -> storage key.
Storage room (locked) -> exit key.
Back corridor (darkest) -> escape zone with exit key -> ESCAPED.

The whole chain is data: required_key on doors, item_id on pickups, required_key on the EscapeZone, and note texts for direction. Re-theme a level by editing strings, not code. Keys live in dead ends so the stalker gets backtracking time; notes double as the hint system - no quest UI.

Escalation timeline (why it works)

Minute 1: quiet, base ambient sounds, flashlight secured. Minute 2-3: first stalker appearance, whispers join the pool. Mid-game: battery pressure, screams, shorter stalker gaps, brief-darkness events. Endgame: tension near 1.0 - vignette closed in, breathing sway, growls, stalker every 8s, in the darkest corridor with the exit key. All of it falls out of one passive float plus event spikes; tune the drain rate, the reappear floor, and ambient intervals - not scripted scares.

Source: library/skills/make-game/references/3d-horror-systems.md, rendered from summer-engine@4.3.0 on npm.

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Video

3D Horror - Systems (Make game skill)

Atmosphere controller (tension in, dread out)

Flickering lights

Positional ambient sounds

Tension events

Stalker AI

Procedural audio

Interactables

HorrorDoor

InteractableItem

EscapeZone

Objective chain

Escalation timeline (why it works)

​Atmosphere controller (tension in, dread out)

​Flickering lights

​Positional ambient sounds

​Tension events

​Stalker AI

​Procedural audio

​Interactables

​HorrorDoor

​InteractableItem

​EscapeZone

​Objective chain

​Escalation timeline (why it works)

Atmosphere controller (tension in, dread out)

Flickering lights

Positional ambient sounds

Tension events

Stalker AI

Procedural audio

Interactables

HorrorDoor

InteractableItem

EscapeZone

Objective chain

Escalation timeline (why it works)