---
title: "Stack timing: API"
package: "@phaser-ae/stack-timing"
tier: Pro
version: 3.0.0-3
released: 2026-10-14
updated: 2026-10-19
description: "One-tap tower-stacking rules, where a slab sweeps over the tower, the overhang is trimmed away and perfect drops snap on and build a streak."
url: https://phaser.io/packs/stack-timing/api
site: Phaser - https://phaser.io
---

# Stack timing: API

`@phaser-ae/stack-timing` — Tap timing for tower stacking: a slab sweeps over the tower, the overhang is cut away, perfect drops snap on and build a streak, as in Stack.

## The pack

### `stackTiming`

```ts
function stackTiming():Pack<{stackTiming:typeof kit}>
```

Install the public rules and seeded generator, independently of rendering.

## Helpers

### `createStackTiming`

```ts
const createStackTiming = (config: StackConfig)=> …
```

Create a round from `config`, the same as `new StackTiming(config)`.

### `generateStackTiming`

```ts
function generateStackTiming(options: StackOptions = {}): StackLevel
```

Generate a tower from `options` and prove it can be built by playing it through the rules. Throws on floors, speed
or tolerance outside their bounds, an unknown difficulty or pattern, a regrow or scoring value out of range, or a
seed outside 0 to 4294967295, and if the replay does not finish the tower.

## Classes

### `StackTiming`

```ts
class StackTiming
```

A stacking round: slabs sweep across and are dropped onto the tower, trimmed to what overlaps.

- `readonly config: StackConfig` — The tower it was created with (an owned copy).
- `constructor(c: StackConfig)`
- `get state()` — A fresh copy of the state.
- `get solved()` — Whether every course has been placed.
- `get lost()` — Whether a drop missed the stack and ended the round.
- `target(): StackSlab | null` — Intended landing footprint; inset courses remain inside the preceding slab.
- `moving(): StackSlab | null` — The sweeping slab now: the target footprint shifted along the stage's axis. Null once the round is solved or lost.
- `step(dt: number)` — Advance the clock by `dt` seconds, moving the slab (it holds still once the round is over). Throws unless `dt` is from 0 to 0.1, so split longer frames.
- `drop()` — Drop the moving slab. Returns `{ valid, reason }`: invalid with 'Round finished' when the round is over, otherwise valid with `reason` `perfect`, `trimmed` or `miss`. A trimmed slab keeps only its overlap; a miss (overlap of 0.035 or less) ends the round.
- `hint()` — `{ wait }`: the seconds from now until the moving slab next crosses its target, where a drop is perfect; null once the round is over. It reads the current state and moves nothing, so stepping exactly `wait` and dropping replays a perfect drop.
- `undo()` — Take back the last drop; false when there is nothing to undo.
- `redo()` — Replay a drop that `undo` took back; false when there is none.
- `reset()` — Rebuild the round from its tower: only the base slab, no score, history cleared.
- `addStages(stages: readonly StackStage[]): number` — Append courses on top of the tower's list, for an endless tower: add more before the player reaches the last. A solved round becomes live again with the next appended course moving. Returns the new number of courses. Throws on a stage value out of range or more than 10000 courses in all.

## Types

### `StackConfig`

```ts
interface StackConfig
```

A whole tower: the base slab, the slab thickness, the perfect window and every course.

- `width: number` — Width (x) of the base slab, world units from 0.5 to 20; each course is cut from the one below.
- `depth: number` — Depth (z) of the base slab, world units from 0.5 to 20.
- `height: number` — Thickness of every slab, world units from 0.1 to 2.
- `perfectTolerance: number` — How far, in world units from 0.001 to 0.5, a drop may be from the target and still count as perfect and snap onto it.
- `stages: StackStage[]` — The courses to place, from the bottom up: from 1 to 10000, a bound that keeps state copies and undo snapshots small. `addStages` appends more during play, for an endless tower.
- `regrow?: StackRegrow` — Regrow the slab after a perfect streak, as in Stack; omit (the default) for no regrowth.
- `scoring?: StackScoring` — Points per drop; omitted fields score as before: perfect 10 plus 2 per streak, trimmed 5.

### `StackLevel`

```ts
interface StackLevel
```

A generated tower and the proof that it can be built.

- `seed: number` — The seed used.
- `difficulty: Difficulty` — The difficulty used.
- `config: StackConfig` — The tower to play: pass it to `createStackTiming`.
- `parameters: Required<StackOptions>` — The options with every default filled in; pass them back to `generateStackTiming` to get the same level.
- `solution: { /** Seconds to step from the moment the course starts moving before dropping it. */ wait: number; }[]` — A winning performance: for each course in turn, the seconds to step before dropping. Replay by stepping exactly that long, then calling `drop`.
- `metrics: { /** The tower family the level was built from, such as 'spiral'. */ family: string; /** Number of courses. */ floors: number; /** The shortest time, in seconds, the moving slab spends inside the perfect window on any course. */ minimumPerfectWindow: number; /** Courses whose sweep axis differs from the one below. */ axisChanges: number; /** JSON fingerprint of the footprint and each course's axis, motion, coarse speed and target, to tell towers apart. */ structure: string; }` — Measurements of the level.

### `StackOptions`

```ts
interface StackOptions
```

Controls for `generateStackTiming`; every one is optional and checked against its bounds.

- `seed?: number` — Unsigned 32-bit seed, 0 to 4294967295. Default 1.
- `difficulty?: Difficulty` — `easy`, `medium`, `hard` or `very-hard`. Default `medium`.
- `floors?: number` — Courses to place, a whole number from 2 to 60. Default 8, 12, 18 or 24 by difficulty, plus 0 to 2 from the seed.
- `speed?: number` — Base sweep rate, world units a second, from 0.5 to 8. Default 1.8, 2.6, 3.5 or 4.5 by difficulty.
- `perfectTolerance?: number` — The perfect window, world units from 0.01 to 0.3. Default 0.18, 0.12, 0.075 or 0.045 by difficulty.
- `pattern?: 'auto' | 'alternating' | 'runs' | 'mixed' | 'terraces' | 'spiral' | 'needle' | 'bridge'` — The tower family: `auto` (default) picks one from the seed. Others are alternating, runs, mixed, terraces, spiral, needle and bridge.
- `regrow?: StackRegrow | null` — Copied into the generated tower's `StackConfig.regrow`; default null, no regrowth.
- `scoring?: StackScoring | null` — Copied into the generated tower's `StackConfig.scoring`; default null, the standard scores.

### `StackRegrow`

```ts
interface StackRegrow
```

The Stack-style regrowth reward: after a run of perfect drops each further perfect drop widens the placed slab along
the axis it swept, never past the base slab's size on that axis.

- `after: number` — Perfect drops in a row, a whole number from 1 to 100, before a perfect drop starts to regrow the slab.
- `by: number` — World units, 0.01 to 5, added to the slab's size on the swept axis by each regrowing perfect drop.

### `StackScoring`

```ts
interface StackScoring
```

Points per drop; every field is optional and defaults as described.

- `perfect?: number` — Points for a perfect drop before the streak bonus, 0 to 1000; default 10.
- `streakBonus?: number` — Extra points per drop of the current perfect streak (counting this drop), added to a perfect drop, 0 to 1000; default 2.
- `trimmed?: number` — Points for a trimmed drop, 0 to 1000; default 5.

### `StackSlab`

```ts
interface StackSlab
```

A placed or moving slab: its centre and size in world units.

- `x: number` — Centre across the width, world units.
- `y: number` — Height in world units: the base slab is 0 and each course sits `config.height` above the one below.
- `z: number` — Centre across the depth, world units.
- `width: number` — Size along x, world units.
- `depth: number` — Size along z, world units.

### `StackStage`

```ts
interface StackStage
```

One course of the tower: how its moving slab sweeps back and forth until the player drops it.

- `axis: 'x' | 'z'` — The axis the moving slab sweeps along: `x` (its width) or `z` (its depth).
- `speed: number` — Sweep rate in world units a second, from 0.1 to 20: the `sine` motion peaks at this speed and the `linear` one moves at 2/π of it.
- `travel: number` — Half the sweep range, world units from 1 to 30: the slab swings between -travel and +travel either side of the target.
- `phase: number` — Starting phase of the sweep in radians, from -100 to 100; the slab begins at the offset `sin(phase) * travel`.
- `motion: 'linear' | 'sine'` — `sine` slows towards each end; `linear` keeps a constant speed and turns sharply.
- `target?: { x: number; z: number; scaleX: number; scaleZ: number; }` — Where this course should land, as an inset of the slab below. Default the whole slab below. `scaleX` and `scaleZ` (0.5 to 1) scale its width and depth, and `x` and `z` (-1 to 1) slide the smaller footprint within the old one, -1 and 1 being flush with its edges.

### `StackState`

```ts
interface StackState
```

The round's state, an owned copy; `StackTiming.state` makes a fresh one each read.

- `time: number` — Seconds stepped since the round started or was reset.
- `stageTime: number` — Seconds since the current slab started to move; back to 0 at every drop.
- `placed: StackSlab[]` — The slabs set so far, the base first; the next course to place is `config.stages[placed.length - 1]`.
- `offcuts: (StackSlab & { born: number; vx: number; vz: number; })[]` — The trimmed overhangs, for the renderer: each carries `born`, the `time` it was cut, and a sideways drift velocity (`vx`, `vz`). They never affect later contacts.
- `streak: number` — Consecutive perfect drops now; a trimmed drop or a miss resets it to 0.
- `bestStreak: number` — The longest streak this round.
- `score: number` — Points: by default a perfect drop scores 10 plus twice the streak so far (counting that drop), a trimmed one 5, a miss 0; `StackConfig.scoring` changes the amounts.
- `lost: boolean` — Whether a drop missed the stack and ended the round.
- `last: 'ready' | 'perfect' | 'trimmed' | 'miss'` — How the last drop went: `ready` before the first, then `perfect`, `trimmed` or `miss`.

### `StackTimingApi`

```ts
type StackTimingApi=typeof kit
```

Public generator and rule constructors exposed on composed games.

---

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