---
title: "Rope physics: API"
package: "@phaser-ae/physics-rope"
tier: Free
version: 3.0.0-0
released: 2026-10-19
updated: 2026-10-19
description: "Ropes, cords and chains for 2D or 3D games that swing, drape, stretch, snap and get cut, carrying loads and tied to fixed, moving or rigid-body anchors."
url: https://phaser.io/packs/physics-rope/api
site: Phaser - https://phaser.io
---

# Rope physics: API

`@phaser-ae/physics-rope` — Ropes, cords and chains that swing, drape, stretch, snap and get cut, carrying loads and tied to fixed, moving or rigid-body anchors.

## The pack

### `physicsRope`

```ts
function physicsRope(options: PhysicsRopeOptions = {}): Pack<{ ropes: RopeWorld }>
```

The `physics-rope` pack: `game.ropes`, a rope world stepped every fixed step, after `physics-2d`, `physics-box2d`
and `physics-3d` so a rope tied to a body sees where the body went this step. Gravity defaults to 900 units/s² down
in a 2D world and 9.81 m/s² down (y up) in a 3D one.

## Functions

### `createRopeWorld`

```ts
function createRopeWorld(options: RopeWorldOptions = {}): RopeWorld
```

Make a rope world. See {@link RopeWorldOptions}.

### `ropeContact`

```ts
function contact(c: RopeCollider, x: number, y: number, z: number, r: number): Contact | null
```

The overlap of a ball at (x, y, z) of radius `r` with a shape, or null when they do not touch.

### `segmentsCross`

```ts
function segmentsCross(p1x: number, p1y: number, p2x: number, p2y: number, q1x: number, q1y: number, q2x: number, q2y: number): boolean
```

Do the 2D segments p1-p2 and q1-q2 cross? Touching counts.

## Classes

### `RopeWorld`

```ts
class RopeWorld
```

The rope world. Make one with {@link createRopeWorld}, or compose the `physics-rope` pack for `game.ropes`.

- `readonly gravity: { x: number; y: number; z: number }` — Gravity, live: change it whenever.
- `constructor(options: RopeWorldOptions = {})`
- `addLoad(spec: RopeLoadSpec): RopeLoad` — Add a load ropes can carry. Returns its handle.
- `load(id: string): RopeLoad | undefined` — A load by id, or undefined.
- `removeLoad(id: string): void` — Remove a load. Ropes tied to it are cut at that end.
- `addRope(spec: RopeSpec): Rope` — Make a rope between two ends. Returns its handle.
- `rope(id: string): Rope | undefined` — A rope by id, or undefined.
- `ropes(): Rope[]` — Every rope still in the world.
- `removeRope(id: string): void` — Remove a rope. Its loads stay.
- `cutAlong(path: ReadonlyArray<RopeVec>): { rope: string; segment: number }[]` — Cut every rope segment the swipe crosses, this step or the last, so a fast swipe cannot pass between frames of a thin rope. The swipe is a polyline in the xy plane. Returns what was cut.
- `nearest(point: RopeVec, within = Infinity): { rope: string; segment: number; distance: number } | null` — The nearest uncut rope segment to a point, within `within` units, or null.
- `addCollider(c: RopeCollider): string` — Add a static collider. Returns its id.
- `removeCollider(id: string): boolean` — Remove a collider.
- `colliders(): RopeCollider[]` — Every collider.
- `step(dt: number): void` — Advance by `dt` seconds of game time, in fixed steps. Call once per game step.
- `drain(): RopeEvent[]` — What happened since the last drain, oldest first.
- `get dropped(): number` — How many events were dropped because nobody drained them (past `limits.events`).
- `diagnostics(): RopeDiagnostics` — The state of the last step.
- `snapshot(): RopeSnapshot` — The whole world as plain JSON. `follow` and `link` anchors are recorded where they are; re-attach them after `restore`.
- `restore(snap: RopeSnapshot): void` — Return to a snapshot. Throws on anything that is not one, leaving the world as it was.

## Types

### `PhysicsRopeOptions`

```ts
type PhysicsRopeOptions = RopeWorldOptions
```

The `physics-rope` options: the world's, with gravity defaulting to the composed world's convention.

### `Rope`

```ts
interface Rope
```

A rope as the world holds it. Read it freely; change it through its methods.

- `readonly id: string` — Its id.
- `readonly radius: number` — Its thickness, a radius.
- `readonly segments: number` — How many segments it has.
- `readonly length: number` — Its rest length now (after any pay-out or reel), the sum of its segments' rest lengths.
- `readonly cuts: ReadonlyArray<boolean>` — Which segments are cut.
- `readonly removed: boolean` — Has it been removed from the world?
- `tension(segment: number): number` — The pull on each segment in the last step, in force units (mass times length per second squared).
- `points(): number[][]` — The particle positions along it, `[x, y, z]` each, from the first end.
- `runs(): number[][]` — The uncut stretches of it as polylines, `[x0, y0, z0, x1, y1, z1, …]`: what to draw.
- `cut(segment: number): void` — Cut a segment (0 is next to the first end). Its momentum is kept on both sides.
- `payOut(d: number): void` — Let out `d` units of rope (negative reels in), between a fifth and four times the length it was made with.
- `attach(end: 'from' | 'to', to: RopeEnd): void` — Tie an end to something else, or set it free (a point).

### `RopeBodyLink`

```ts
interface RopeBodyLink
```

A rigid body a rope end is tied to, from any physics pack: the rope pulls it and it pulls the rope. Give its mass,
where it is, and how to push it; see the page for `physics-2d`, `physics-box2d` and `physics-3d` adapters.

- `readonly mass: number` — The body's mass, in the same units as rope and load masses.
- `position(): RopeVec` — Where the tie point is now, in world units.
- `push(ix: number, iy: number, iz: number): void` — Apply an impulse (mass times velocity change) at the tie point.

### `RopeCollider`

```ts
type RopeCollider = /** A circle in 2D, a sphere in 3D (give `z`). */ | { kind: 'circle'; id?: string; x: number; y: number; z?: number; radius: number; friction?: number } /** A segment with thickness: a peg, a bar, a branch. */ | { kind: 'capsule'; id?: string; ax: number; ay: number; az?: number; bx: number; by: number; bz?: number; radius: number; friction?: number } /** * A rectangle centred on (x, y), turned by `angle` radians about z. Give `depth` (and `z`) for a box in 3D; * without it the box reaches through every z. */ | { kind: 'box'; id?: string; x: number; y: number; z?: number; width: number; height: number; depth?: number; angle?: number; friction?: number } /** A convex polygon in the xy plane, its points in either winding. */ | { kind: 'polygon'; id?: string; points: ReadonlyArray<readonly [number, number]>; friction?: number } /** Thin walls along a polyline in the xy plane, closed or open, with an optional thickness. */ | { kind: 'chain'; id?: string; points: ReadonlyArray<readonly [number, number]>; closed?: boolean; radius?: number; friction?: number } /** Everything on the far side of a line (2D) or plane (3D): the points where n·p < offset are inside. */ | { kind: 'plane'; id?: string; nx: number; ny: number; nz?: number; offset: number; friction?: number }
```

A static shape ropes and loads collide with. `friction` (default 0.3) slows sliding along it, 0 is ice, 1 grips.

### `RopeContact`

```ts
interface RopeContact
```

Where a ball overlaps a shape: the unit normal out of the shape and how deep it is.

- `nx: number` — The unit normal pointing out of the shape, towards the ball: x.
- `ny: number` — The normal's y.
- `nz: number` — The normal's z (0 in 2D).
- `depth: number` — How far the ball must move along the normal to just touch.

### `RopeDiagnostics`

```ts
interface RopeDiagnostics
```

What the world reports about its last step.

- `time: number` — Simulated seconds so far.
- `substeps: number` — Substeps the last fixed step was split into.
- `saturated: number` — Fixed steps so far that needed more than `maxSubsteps`: fast motion the solver had to run short.
- `maxStretch: number` — The worst stretch of any segment beyond its rest length, as a fraction.
- `maxTension: number` — The largest segment tension.
- `kineticEnergy: number` — Kinetic energy of everything that moves.
- `settled: boolean` — True when nothing moves faster than a tenth of a radius per second.

### `RopeEnd`

```ts
type RopeEnd = /** Hanging free, starting here. */ | RopeVec /** Fixed at a point: a hook, a nail, a ceiling. */ | { fixed: RopeVec } /** Tied to a load made with `addLoad`, which the rope then carries. */ | { load: string } /** Moving with whatever the function says each step: a rotating hook, a sliding rail, a hand. */ | { follow: () => RopeVec } /** Tied to a body of a physics pack, pulling and pulled. */ | { link: RopeBodyLink }
```

What a rope end is tied to.

### `RopeEvent`

```ts
type RopeEvent = | { kind: 'cut'; rope: string; segment: number; cause: 'call' | 'swipe' | 'tear' } | { kind: 'contact'; load: string; collider: string }
```

Something that happened in a step, for a game to react to.

### `RopeLoad`

```ts
interface RopeLoad
```

A load as the world holds it: live position and velocity.

- `readonly id: string` — Its id.
- `readonly x: number` — Where it is, across.
- `readonly y: number` — Where it is, along y.
- `readonly z: number` — Where it is, along z (0 in 2D).
- `readonly vx: number` — How fast it is moving along x, units per second.
- `readonly vy: number` — How fast it is moving along y.
- `readonly vz: number` — How fast it is moving along z.
- `readonly radius: number` — Its radius.
- `gravityScale: number` — Its gravity multiplier; set it to make a bubble rise (negative) or float (0).
- `impulse(ix: number, iy: number, iz?: number): void` — Push it: an impulse, mass times velocity change.
- `place(x: number, y: number, z?: number, vx?: number, vy?: number, vz?: number): void` — Put it somewhere, at rest or with a velocity.

### `RopeLoadSpec`

```ts
interface RopeLoadSpec
```

A load a rope can carry: Cut the Rope's candy, a crate, a hanging lamp.

- `id: string` — A unique id.
- `x: number` — Where it starts, across.
- `y: number` — Where it starts, along y.
- `z?: number` — Where it starts, along z (3D). Default 0.
- `radius: number` — Its radius, for colliders and other loads.
- `mass?: number` — Its mass. Default 10.
- `gravityScale?: number` — Gravity multiplier: 0 floats, negative rises (a bubble). Default 1.
- `vx?: number` — Its starting velocity along x, units per second. Default 0.
- `vy?: number` — Its starting velocity along y. Default 0.
- `vz?: number` — Its starting velocity along z (3D). Default 0.

### `RopeSnapshot`

```ts
interface RopeSnapshot
```

A whole world as plain JSON, from `snapshot`. Functions (`follow`, `link`) are not saved: re-attach them after `restore`.

- `format: 'phaser-ae-rope'` — Always `'phaser-ae-rope'`.
- `version: 1` — The snapshot format's version, 1.
- `time: number` — Seconds simulated.
- `accumulator: number` — Time carried over to the next fixed step, seconds.
- `saturated: number` — How many steps ran short of substeps so far.
- `particles: { x: number[]; y: number[]; z: number[]; vx: number[]; vy: number[]; vz: number[]; inv: number[]; radius: number[]; gravity: number[]; load: (string | null)[] }` — Every particle, as parallel arrays: position, velocity, inverse mass, radius, gravity scale, and its load id.
- `ropes: { id: string; particles: number[]; base: number[]; scale: number; cuts: boolean[]; radius: number; stretch: number; bend: number | null; tear: number | null; removed: boolean }[]` — `tear` is null for a rope that never tears (JSON has no Infinity).
- `anchors: { particle: number; kind: 'fixed' | 'follow' | 'link'; x: number; y: number; z: number }[]` — Every held particle and where it was held (a `follow` or `link` end is restored as fixed there).
- `colliders: RopeCollider[]` — The colliders.
- `nextId: number` — The counter that names ropes made without an id.

### `RopeSpec`

```ts
interface RopeSpec
```

A rope to make.

- `id?: string` — A unique id. Default one is made.
- `from: RopeEnd` — The first end.
- `to: RopeEnd` — The second end.
- `length?: number` — The rope's rest length. Default: the distance between the ends as made, times `1 + slack`, so a rope made between two points hangs from them.
- `slack?: number` — Extra length beyond the distance between the ends, as a fraction. Default 0: taut. Ignored when `length` is given.
- `radius?: number` — The thickness, a radius, in world units. Default 2 (pixel-sized 2D worlds); a 3D game in metres wants about 0.02.
- `segments?: number` — How many segments. Default: enough that each is about two radii long, which keeps colliders from slipping through.
- `mass?: number` — The rope's whole mass. Default 1. Loads are usually much heavier.
- `stretch?: number` — Stretch compliance, 0 inextensible (default 0), larger is elastic: about 1e-4 is a bungee.
- `bend?: number` — Bend compliance: how easily the rope folds. Leave it out for a rope that folds freely, as a rope or a chain does (the default): a slack rope then holds nothing up. Give one for a cord or cable that resists folding: smaller is stiffer, 0 a rod; about 0.02 suits a cord of mass 1, and a lighter rope needs a larger value to be as floppy.
- `tear?: number` — A segment pulled harder than this (force units) snaps. Default Infinity: never.

### `RopeVec`

```ts
interface RopeVec
```

A position. `z` is 0 when left out, which is every 2D game.

- `x: number` — Across.
- `y: number` — Down in a 2D game (y down), up in a 3D one (y up).
- `z?: number` — Depth, 3D only. Default 0.

### `RopeWorldOptions`

```ts
interface RopeWorldOptions
```

How a rope world behaves.

- `gravity?: RopeVec` — Gravity, units per second squared. Default `{ x: 0, y: 900 }`: a 2D world, y down. A 3D world in metres wants `{ x: 0, y: -9.81, z: 0 }`.
- `step?: number` — Fixed step, seconds. Default 1/120.
- `iterations?: number` — Constraint passes per substep. Default 8; more is stiffer and costs more.
- `maxSubsteps?: number` — The most substeps one fixed step may take. Default 16.
- `damping?: number` — Velocity damping per second (air). Default 0.2.
- `ropeContact?: boolean` — Do ropes collide with each other and with loads? Default false (Cut the Rope's ropes pass through each other).
- `flat?: boolean` — Keep everything in the z = 0 plane. Default true unless gravity has a z.
- `limits?: { particles?: number; ropes?: number; colliders?: number; events?: number }` — Resource bounds, so a runaway level fails loudly: particles (default 8192), ropes (512), colliders (1024), events kept (256).

---

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