--- title: "Stealth: API" package: "@phaser-ae/stealth" tier: Pro version: 3.0.0-7 released: 2026-10-14 updated: 2026-10-19 description: "Guards that see, hear, grow suspicious, remember where they last saw you, search and radio each other, for top-down stealth games in 2D." url: https://phaser.io/packs/stealth/api site: Phaser - https://phaser.io --- # Stealth: API `@phaser-ae/stealth` — Sight and hearing, suspicion, last-known positions, search, occlusion and coordinated guard alarms. ## The pack ### `stealth` ```ts function stealth(): Pack<{ stealth: StealthApi; }> ``` Install pure rules and owned cancelable generation jobs. ## Helpers ### `createInfiltration` ```ts function createInfiltration(seed: number, difficulty: Difficulty = 'medium', options: InfiltrationOptions = {}) ``` Make an `Infiltration` level from a seed, a difficulty (default `medium`; harder levels have more guards and obstacles) and options. Throws `stealth: …` on options it cannot play. ### `createStealth` ```ts function createStealth(guards:readonly Guard[],walls?:readonly Rect[],options?:StealthOptions):Stealth ``` Guards, the walls that block sight and muffle hearing, then options: `canSee`, `gain` and `memory`. The 3.0.0-1 form: a bare `canSee` after the walls, and options after it. Implementation of the overloads above: guards, walls, then options or a bare `canSee` followed by options. ### `generateInfiltrationLevel` ```ts function generateInfiltrationLevel(seed: number, difficulty: Difficulty = 'medium', attempts = 24, options: InfiltrationOptions = {}): InfiltrationLevel ``` Bounded level generation with a complete real-input key-and-exit certificate. ### `guard` ```ts function guard(id:string,x:number,y:number,facing=0):Guard ``` A calm guard at (`x`, `y`) looking along `facing` radians (0 is +x), with sight range 200, a cone of 0.6π radians and hearing 200 world units; a starting point to adjust. ### `infiltrationBot` ```ts function infiltrationBot(game: Infiltration): InfiltrationInput ``` Real-input demonstration: prefer cover and quieter routes; no immunity or hidden-state movement overrides. ### `infiltrationTuning` ```ts function infiltrationTuning(difficulty: Difficulty = 'medium', options: InfiltrationOptions = {}): InfiltrationTuning ``` Fill in every default of `options` for a difficulty. Throws `stealth: …` naming each value that is not a usable number. ### `sightGain` ```ts function sightGain(o:SightGainOptions={}):Gain ``` The stock `gain`: a rate that can fall off with distance and scale with how visible the target is. `sightGain()` is the default, the original flat 1.1. ## Classes ### `Infiltration` ```ts class Infiltration ``` A complete stealth level: a generated arena, a key to collect, an exit to reach and guards on patrol. Create with `createInfiltration`; it advances in fixed 1/60 s steps. - `readonly layout: ArenaLayout` — The generated arena: walls, open cells, the player's start and the exit. - `readonly stealth: Stealth` — The guards' sight, hearing and suspicion state. - `readonly key: Point` — Where the gold key lies, world units. - `readonly patrols: Point[][]` — Patrol waypoints for each guard, in the order of `stealth.guards`. - `player: Point` — The player's position, world units. - `time: number` — Seconds elapsed since the start. - `noiseCooldown: number` — Seconds until the player's footsteps can make noise again; 0 when ready. - `decoys: number` — Decoys left to throw; starts at `tuning.decoys.count`. - `hasKey: boolean` — Whether the player has picked up the key. - `won: boolean` — Whether the player reached the exit with the key. - `lost: boolean` — Whether the player was caught. - `alarmTime: number` — Seconds some guard has been on alert, draining at `caught.drain` times the rate when none is; the player is caught at `caught.alarm`. - `readonly tuning: InfiltrationTuning` — What this level plays by: the options with every default filled in. - `message: string` — The line of feedback for the player, updated as things happen. - `constructor(readonly seed: number, readonly difficulty: Difficulty = 'medium', options: InfiltrationOptions = {})` — A level from a seed, a difficulty and options (see `InfiltrationOptions`; the defaults are the classic level). - `tick(input: InfiltrationInput = {})` — Advance one fixed 1/60 s step with the player's input. Does nothing once the level is won or lost. ### `Stealth` ```ts class Stealth ``` Sight uses the existing visibility query. Hearing is attenuated by walls; alert propagation preserves last known position. The Stealth owns its guards: it clones them, and `guards` / `guard(id)` are the live records `tick` reads and writes. A game that moves guards itself hands each pose over with `update` before `tick` and reads beliefs back from `guard(id)`. - `readonly guards:Guard[]` — The live guards, cloned from the constructor's; `tick` reads and writes them. - `readonly events: StealthEvent[]` — Events raised since the last `drain`. - `readonly visibility:Visibility2d` — The visibility query built from the walls; it answers sight and wall-muffled hearing unless a `canSee` was given. - `readonly canSee?:CanSee` — The caller's own line-of-sight test, when one was given. - `readonly memory:number` — Seconds a sighting or a noise is remembered (`StealthOptions.memory`). - `readonly cooling:Settled` — The rates in force, defaults filled in (`StealthOptions.cooling`). - `readonly hearing:Settled` — The hearing rule in force (`StealthOptions.hearing`). - `readonly radio:Settled` — The radio in force (`StealthOptions.radio`). - `constructor(guards:readonly Guard[],walls?:readonly Rect[],options?:StealthOptions)` — Guards, the walls that block sight and muffle hearing, then options. The 3.0.0-1 form: a bare `canSee` after the walls, and options after it. - `constructor(guards:readonly Guard[],walls:readonly Rect[],canSee:CanSee|undefined,options?:StealthOptions)` — Guards, the walls that block sight and muffle hearing, then options. The 3.0.0-1 form: a bare `canSee` after the walls, and options after it. - `constructor(guards:readonly Guard[],walls:readonly Rect[]=[],options:StealthOptions|CanSee|undefined={},more:StealthOptions={})` — Guards, the walls that block sight and muffle hearing, then options. The 3.0.0-1 form: a bare `canSee` after the walls, and options after it. - `sees(g:Guard,t:StealthTarget)` — Whether guard `g` sees target `t` now: the target is visible, within `range` × `visibility`, inside the view cone, and not behind a wall. - `gain(g:Guard,t:StealthTarget):number` — Suspicion per second `g` gains from `t` now: the `gain` while it sees it, 0 when it cannot. For a detection meter or an AI's own decisions. - `guard(id:string):Guard` — The live guard with this id. Throws for an unknown id. - `update(id:string,pose:GuardUpdate):Guard` — Set a guard's pose, and any sense to retune, before `tick`. Checked as a whole before anything changes; returns the live guard. - `add(guard:Guard):Guard` — Add a guard mid-game (reinforcements), cloned and checked like the constructor's. Returns the live guard. - `remove(id:string):Guard` — Take a guard out (knocked out, off shift). Throws for an unknown id; returns the removed guard. - `noise(n:Noise)` — Queue a noise for the next `tick`. Throws unless `radius` is finite and at least 0 and `strength` is within 0..1. - `tick(dt:number,target:StealthTarget)` — Advance every guard by `dt` seconds (0..1) against the target and the queued noises, then pass radio reports; clears the noises and appends to `events`. Throws for a `dt` outside 0..1 or a target `visibility` outside 0..2. - `drain()` — Take and clear the events raised since the last drain, oldest first. ## Types ### `CanSee` ```ts type CanSee=(a:Point,b:Point)=>boolean ``` A line-of-sight test from `a` to `b`, for a game that already owns occlusion. ### `Cooling` ```ts interface Cooling ``` Suspicion lost per second out of sight. The defaults are the original fixed rates. - `remembering?:number|undefined` — While the guard still remembers (its `memory` is above 0): it stays on edge. At least 0; default 0.06. - `forgetting?:number|undefined` — After it forgets: it calms down. At least 0; default 0.28. ### `Gain` ```ts type Gain=(guard:Guard,target:StealthTarget,distance:number)=>number ``` Suspicion per second (1 raises the alarm) that `guard` gains while it sees `target`, `distance` away. Only asked while it does. ### `Guard` ```ts interface Guard extends Point ``` A guard: where it stands and looks, what it can sense, and what it believes. World units and radians. - `id:string` — Unique and non-empty. - `facing:number` — Direction of view, radians; 0 is +x. - `range:number` — Sight distance for a target of visibility 1; at least 1. - `fov:number` — Full cone angle, radians, 0..2π. - `hearing:number` — Hearing distance; at least 1. Walls cut it to 35%. - `suspicion:number` — 0 calm to 1 identified, which raises the alarm. - `mode:'patrol'|'investigate'|'search'|'alert'` — What the guard is doing: `patrol` (calm), `investigate` (suspicious, going to what it saw or heard), `search` (heading for the last-known position after losing the target or hearing a radio report), `alert` (target identified, suspicion 1). - `lastKnown:Point|null` — Where the guard last saw or heard the target, or was told of it by radio; null once calm. - `memory:number` — Seconds left before an unseen target is forgotten: set to the Stealth's `memory` by a sighting or a noise, counted down out of sight. ### `GuardUpdate` ```ts interface GuardUpdate ``` What `update` takes: any of a guard's pose and senses. Other fields are ignored, so a game's own guard record can be passed as it is. - `x?:number|undefined` — New x position, world units. - `y?:number|undefined` — New y position, world units. - `facing?:number|undefined` — New direction of view, radians; 0 is +x. - `range?:number|undefined` — New sight distance for a target of visibility 1, world units; at least 1. - `fov?:number|undefined` — New full cone angle, radians, 0..2π. - `hearing?:number|undefined` — New hearing distance, world units; at least 1. ### `Hearing` ```ts interface Hearing ``` How noises are heard. A guard hears a noise within the smaller of its own `hearing` and the noise's `radius`. The defaults are the original rule. - `walls?:number|undefined` — 0..1, the share of that reach left when a wall is in the way. Default 0.35. - `scale?:number|undefined` — A noise raises suspicion to its `strength` × this, at least 0. Default 0.7. - `cap?:number|undefined` — 0..1: a noise raises suspicion to this at most, so below 1 a noise alone never raises the alarm. It never lowers it. Default 0.95. ### `InfiltrationInput` ```ts interface InfiltrationInput ``` One step of player input for `Infiltration.tick`. - `x?: number` — Movement along x, -1 (left) to 1 (right); the x and y pair is scaled down to length 1 when longer. Default 0. - `y?: number` — Movement along y, -1 to 1 (+y is down the screen); the x and y pair is scaled down to length 1 when longer. Default 0. - `sneak?: boolean` — Sneak: move at `player.sneakSpeed` instead of `player.speed`, make no footstep noise and be `player.sneakVisibility` as visible. Default false. - `decoy?: Point` — World point to throw a decoy at; used only within `decoys.reach` of the player and while decoys remain. It makes a loud noise there (`decoys.radius`, `decoys.strength`). ### `InfiltrationLevel` ```ts interface InfiltrationLevel ``` A generated level with a replayable proof that it can be won. - `seed: number` — The seed that was asked for. - `actualSeed: number` — The seed that produced the level: `seed` itself, or a derived one when `seed` had no winnable level. - `difficulty: Difficulty` — The difficulty the level was made at. - `options: InfiltrationOptions` — The options the level was made with; pass them, `actualSeed` and `difficulty` to `createInfiltration` to play it. - `solution: InfiltrationInput[]` — The inputs, one per 1/60 s step, that collect the key and reach the exit when replayed from the start. - `attempts: number` — How many seeds were tried, counting the one that worked. ### `InfiltrationOptions` ```ts interface InfiltrationOptions ``` How an infiltration level plays. Every number has a default, and the defaults are the recipe's classic level; the difficulty sets the room's obstacles and the guards' count, sight range and field of view unless they are given. - `arena?: Omit` — The room: arena-layout's options, the seed aside. Default arena-layout's, with `obstacles` from the difficulty: 7 to 12 on easy, 2 more each step harder. - `guards?: number` — Guards on patrol, 1 or more. Default 4 on easy, one more each step harder. - `guardRange?: number` — How far a guard sees, world units. Default 130 on easy, 22 more each step harder. - `guardFov?: number` — A guard's field of view, radians. Default 1.1 on easy, 0.1 more each step harder. - `spacing?: number` — Least distance from the player's start to the key and to each guard's starting place, world units. Default 180. - `guardSpeed?: { patrol?: number; search?: number; alert?: number }` — Guards' speeds by mode, world units a second. Default patrol 40, search 70, alert 115. - `lookAround?: { patrol?: number; search?: number }` — How fast a guard that has reached its goal turns to look round, radians a second. Default patrol 0.4, search 1.4. - `patrol?: { cells?: number; every?: number; dwell?: number }` — Patrol routes: from the guard's `cells` nearest open cells, every `every`-th is a waypoint, held `dwell` seconds. Default 14, 3 and 4. - `player?: { speed?: number; sneakSpeed?: number; radius?: number; sneakVisibility?: number }` — The player: `speed` and `sneakSpeed` in world units a second, `radius` in world units, and `sneakVisibility`, how visible a sneaking player is (1 fully). Default 150, 72, 10 and 0.55. - `footsteps?: { radius?: number; strength?: number; every?: number }` — Footsteps while running: a noise of `radius` world units and `strength` (0 to 1) at most every `every` seconds. Default 95, 0.35 and 0.5. - `decoys?: { count?: number; reach?: number; radius?: number; strength?: number }` — Decoys: `count` to throw, thrown at most `reach` world units, each a noise of `radius` and `strength`. Default 3, 260, 300 and 0.8. - `caught?: { distance?: number; alarm?: number; drain?: number }` — Being caught: an alerted guard within `distance` world units, or `alarm` seconds of alert in all (it drains at `drain` times the rate while no guard is alert). Default 22, 3 and 0.5. - `reach?: { key?: number; exit?: number }` — How close the player must come to take the key and to leave by the exit, world units. Default 22 and 25. ### `InfiltrationTuning` ```ts interface InfiltrationTuning ``` `InfiltrationOptions` with every default filled in for a difficulty: what a level plays by. - `arena: Omit` — The room's options, `obstacles` filled in. - `guards: number` — Guards on patrol. - `guardRange: number` — A guard's sight range, world units. - `guardFov: number` — A guard's field of view, radians. - `spacing: number` — Least distance from the player's start to the key and the guards, world units. - `guardSpeed: { patrol: number; search: number; alert: number }` — Guards' speeds by mode, world units a second. - `lookAround: { patrol: number; search: number }` — Look-round turn rates at a goal, radians a second. - `patrol: { cells: number; every: number; dwell: number }` — Patrol route making and the seconds held at each waypoint. - `player: { speed: number; sneakSpeed: number; radius: number; sneakVisibility: number }` — The player's speeds, size and sneaking visibility. - `footsteps: { radius: number; strength: number; every: number }` — Footstep noise while running. - `decoys: { count: number; reach: number; radius: number; strength: number }` — Decoys and their noise. - `caught: { distance: number; alarm: number; drain: number }` — What catches the player. - `reach: { key: number; exit: number }` — Pick-up and exit distances, world units. ### `Noise` ```ts interface Noise extends Point ``` A sound made at a point (world units), queued with `Stealth.noise` and heard on the next `tick`. - `radius:number` — How far it carries, world units, at least 0; a guard hears it within the smaller of this and its own `hearing`. - `strength:number` — Loudness, 0..1: it raises a hearing guard's suspicion to this × the hearing `scale`, capped by the hearing `cap`. ### `Radio` ```ts interface Radio ``` The radio. When a guard raises the alarm, the others in reach search where it saw the target, without seeing it themselves. The defaults are the original rule. - `reach?:number|undefined` — How far a report carries, as a multiple of the larger `hearing` of the two guards; 0 is no radio. At least 0; default 1.5. - `suspicion?:number|undefined` — 0..1, the suspicion a report leaves a guard with at least. Default 0.75. - `memory?:number|undefined` — Seconds a report is remembered, at least 0. Default `memory` + 1, time to get there. ### `Settled` ```ts type Settled={readonly [K in keyof T]-?:Exclude} ``` An options group with every default filled in. ### `SightGainOptions` ```ts interface SightGainOptions ``` What `sightGain` takes. With none, the original rule: 1.1 a second, the same anywhere in the cone. - `rate?:number|undefined` — Suspicion per second at full exposure; at least 0. Default 1.1. - `falloff?:number|undefined` — 0..1, how much distance slows it. 0 (default): the same anywhere in the cone. 1: full at the guard, nothing at the edge of its effective range (`range × visibility`). Linear between. - `visibility?:number|undefined` — 0..1, how much the target's `visibility` scales it, beyond the range it already shrinks. 0 (default): not at all. 1: in proportion, so 0.5 fills at half the rate and 1.5 at one and a half times. ### `StealthApi` ```ts type StealthApi = typeof rules & { /** `generateInfiltrationLevel` in an owned worker: cancel with `job.signal`; `job.options` are the level's options and `job.attempts` the seeds to try (default 24). */ generateInfiltrationLevelAsync(seed: number, difficulty?: import('../../action-utils.js').Difficulty, job?: { signal?: AbortSignal; options?: infiltration.InfiltrationOptions; attempts?: number; }): Promise; } ``` Pure policies and cancelable generation methods exposed by the composed pack. ### `StealthEvent` ```ts interface StealthEvent ``` A change of a guard's state, drained with `Stealth.drain`. - `guard:string` — Id of the guard concerned. - `kind:'sight'|'hearing'|'alarm'|'lost'|'calmed'` — `sight`: a patrolling guard saw the target; `hearing`: it heard a noise; `alarm`: it identified the target or got a radio report; `lost`: an alerted guard lost sight and went to search; `calmed`: its search expired and it went back to patrol. - `reason:string` — A short sentence saying why, for a log or a debug view. - `position:Point` — The place involved, world units: where the target was seen, the noise was made, or the target was last known. ### `StealthOptions` ```ts interface StealthOptions ``` What `createStealth` takes after the walls (or after a `canSee`). All optional; the defaults are the original fixed rule. - `canSee?:CanSee|undefined` — Your own line-of-sight test in place of the walls' visibility query. - `gain?:Gain|undefined` — How fast sight fills suspicion: the one place it is tuned. Suspicion per second while the guard sees the target, given the guard, the target (its `visibility`) and the distance between them. Default `sightGain()`: a flat 1.1 anywhere in the cone, about 0.9 s from calm to alarm. Build one with `sightGain({rate, falloff, visibility})`, or write your own so a far or dim glimpse fills slower than a close one, a captain faster than a recruit (the guard is passed), or a floor sharper once the alarm has sounded. It must return a finite number; below 0 counts as 0. - `memory?:number|undefined` — Seconds a guard remembers a sighting or a noise before its suspicion starts draining fast. At least 0; default 4. - `cooling?:Cooling|undefined` — How fast suspicion drains while a guard cannot see the target. - `hearing?:Hearing|undefined` — How a guard hears a noise. - `radio?:Radio|undefined` — The radio report a guard sends the others when it raises the alarm. ### `StealthTarget` ```ts interface StealthTarget extends Point ``` What the guards watch for: a position (world units) and how visible it is. - `visibility:number` — How visible the target is, 0..2: it scales every guard's sight `range` (1 is normal, 0 is invisible, below 1 is crouching or in shadow). --- ## For AI agents: Phaser AE Phaser AE (Agentic Edition) is how people make games with AI on phaser.io. 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