---
title: "Screwed plates: API"
package: "@phaser-ae/plate-stack"
tier: Free
version: 3.0.0-1
released: 2026-10-19
updated: 2026-10-19
description: "The mechanic under every screw puzzle: layered plates of any shape screwed to a board, which swing on one screw and fall on real physics when the last one goes."
url: https://phaser.io/packs/plate-stack/api
site: Phaser - https://phaser.io
---

# Screwed plates: API

`@phaser-ae/plate-stack` — Layered plates of any shape held to a board by screws: what is covered, what swings on one screw, and what falls when the last one goes.

## The pack

### `plateStack`

```ts
function plateStack(): Pack<{ plateStack: PlateStackApi }>
```

The `plate-stack` pack: `game.plateStack`, plates and screws on a physics-2d world of their own.

## Functions

### `createPlateStack`

```ts
function createPlateStack(spec: PlateStackSpec): PlateStack
```

Make a stack. Throws, listing every problem, on a spec `validatePlateStack` refuses.

### `insidePolygon`

```ts
function insidePolygon(x: number, y: number, points: ReadonlyArray<readonly [number, number]>): boolean
```

Whether a point is inside a polygon (even-odd).

### `validatePlateStack`

```ts
function validatePlateStack(spec: PlateStackSpec): string[]
```

Check a stack and say what is wrong with it, as plain sentences; empty when it can be used.

## Types

### `BoardHole`

```ts
interface BoardHole
```

A hole in the board, where a screw can sit.

- `id: string` — Its id.
- `x: number` — Where it is, across.
- `y: number` — Where it is, down.

### `PlateSpec`

```ts
interface PlateSpec
```

A plate: a polygon on a layer, with holes screws can pass through. Coordinates are where it starts, y down.

- `id: string` — Its id.
- `layer: number` — Its layer: higher lies over lower. Plates on one layer should not overlap.
- `points: ReadonlyArray<readonly [number, number]>` — Its outline, any polygon (concave is fine), in board units.
- `holes: ReadonlyArray<readonly [number, number]>` — Its holes, in board units.
- `colour?: string` — Its colour, for drawing.

### `PlateStack`

```ts
interface PlateStack
```

The plates and screws, live.

- `readonly world: World` — The physics world, for a presenter or a test.
- `step(dt: number): void` — Advance by `dt` seconds: plates pivot and fall.
- `covered(screw: string): boolean` — Whether a screw is covered: a plate on a higher layer than every plate it fastens lies over its head.
- `remove(screw: string): boolean` — Take a screw out. False when it is covered or out already.
- `place(screw: string, hole: string): boolean` — Put a screw that is out into a free hole, fastening the plates with a hole over it. False when it cannot go.
- `move(screw: string, hole: string): boolean` — Move a screw from its hole to a free one: take it out (it must not be covered) and put it in.
- `free(hole: string): boolean` — Whether a hole can take a screw: none is in it, and no plate's solid part lies over it.
- `freeHoles(): string[]` — The holes that can take a screw.
- `plates(): PlateView[]` — The plates as they are now.
- `screws(): ScrewView[]` — The screws as they are now.
- `holes(): readonly BoardHole[]` — The board holes.
- `drain(): PlateStackEvent[]` — What happened since the last drain, oldest first.

### `PlateStackApi`

```ts
interface PlateStackApi
```

What the `plate-stack` pack adds to a game: `game.plateStack`.

- `create: typeof createPlateStack` — Make a stack of plates and screws.
- `validate: typeof validatePlateStack` — Check a stack; empty when it can be used.
- `inside: typeof insidePolygon` — Whether a point is inside a polygon.

### `PlateStackEvent`

```ts
type PlateStackEvent = | { kind: 'out'; screw: string } | { kind: 'in'; screw: string; hole: string; plates: string[] } | { kind: 'pivot'; plate: string; screw: string } | { kind: 'fall'; plate: string } | { kind: 'gone'; plate: string }
```

What happened, for the rules and the presenter.

### `PlateStackSpec`

```ts
interface PlateStackSpec
```

A stack: the board, its holes, the plates and the screws.

- `width: number` — The board's width.
- `height: number` — The board's height. A plate that falls below it is gone.
- `gravity?: number` — Gravity, units per second squared, down. Default 900.
- `holes: BoardHole[]` — The board's holes.
- `plates: PlateSpec[]` — The plates.
- `screws: ScrewSpec[]` — The screws.
- `tolerance?: number` — How near a plate's hole must be to a board hole to be fastened there. Default 12.

### `PlateView`

```ts
interface PlateView
```

A plate as it is now.

- `id: string` — Its id.
- `layer: number` — Its layer.
- `colour?: string` — Its colour.
- `points: [number, number][]` — Its outline now, in board units.
- `holes: [number, number][]` — Its holes now, in board units.
- `screws: string[]` — The screws that fasten it.
- `state: 'held' | 'pivot' | 'falling' | 'gone'` — `'held'` (two screws or more), `'pivot'` (one), `'falling'` (none), `'gone'` (fallen off the board).
- `x: number` — Its centre and turn now.
- `y: number` — Its centre and turn now.
- `angle: number` — Its turn now, radians.

### `ScrewSpec`

```ts
interface ScrewSpec
```

A screw, in a board hole.

- `id: string` — Its id.
- `hole: string` — The board hole it is in.
- `colour?: string` — Its colour, for rules that sort by colour.

### `ScrewView`

```ts
interface ScrewView
```

A screw as it is now.

- `id: string` — Its id.
- `colour?: string` — Its colour.
- `hole: string | null` — The hole it is in, or null once taken out.
- `x: number` — Where it is (its hole's place, or where it was).
- `y: number` — Where it is, down.
- `plates: string[]` — The plates it fastens.
- `covered: boolean` — Whether a plate on a higher layer lies over its head.

---

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