---
title: "Vector Motion: API"
package: "@phaser-ae/vector-motion"
tier: Free
version: 3.0.0-3
released: 2026-10-14
updated: 2026-10-20
description: "Moves a 2D body one frame and keeps it on screen, with thrust, drag and a speed cap, point gravity, path prediction and wrap-around screen edges."
url: https://phaser.io/packs/vector-motion/api
site: Phaser - https://phaser.io
---

# Vector Motion: API

`@phaser-ae/vector-motion` — Advance a body one frame and keep it on screen: integration, point gravity, path prediction and screen wrap.

## The pack

### `vectorMotion`

```ts
function vectorMotion(): Pack<{ vecMotion: VecMotionApi }>
```

The `vector-motion` pack. Pure maths, so it needs no backend and runs headless.

## Helpers

### `integrateMotion`

```ts
function integrateMotion(body: Body, opts: MotionOptions): void
```

Advance a bare body one frame, in place — semi-implicit Euler (velocity before
position; stable under gravity and frame-rate independent) with a
terminal-speed clamp.

### `wrapPositions`

```ts
function wrapPositions(position: Vec2, radius: number, width: number, height: number): Vec2[]
```

Return every screen position at which a wrapping sprite should be drawn this
frame — the real position plus mirrors for each edge the sprite straddles
(corners yield the diagonal mirror too, so up to 4 positions).

## Functions

### `gravityAccel`

```ts
function gravityAccel(pos: Vec2, sources: GravitySource[], opts: GravityOptions = {}): Vec2
```

The summed inverse-square gravitational acceleration on a body at `pos` from
all `sources` (softened — no singularity at the centre). Add it to the body's
accel before `integrateMotion`; apply to ships AND bullets so shots curve too.

### `predictPath`

```ts
function predictPath( body: Body, accelFn: (state: Body) => Vec2, steps: number, dt: number, opts: { maxSpeed?: number; drag?: number } = {}, ): Vec2[]
```

Forward-simulate a body under an acceleration function, returning sampled
positions (steps + 1, starting at the current position) — aim arcs, shot
previews. Pass the SAME acceleration the physics uses so the prediction matches.

### `wrapPosition`

```ts
function wrapPosition(position: Vec2, width: number, height: number): void
```

Wrap a position back into `[0, width) × [0, height)` after integrating
movement. Mutates `position` in place. Call once per frame.

## Types

### `Body`

```ts
interface Body
```

A bare point body for `integrateMotion`/`predictPath`.

- `x: number` — The world x position of the body.
- `y: number` — The world y position of the body.
- `vx: number` — The horizontal speed, in world units each second.
- `vy: number` — The vertical speed, in world units each second. Positive is down.

### `GravityOptions`

```ts
interface GravityOptions
```

Tuning for `gravityAccel`.

- `G?: number` — Gravitational constant — scales how deep every well feels. Default 1.
- `minR2?: number` — Softening floor on r² (> 0) so the pull never blows up at a well's centre. Default 1.

### `GravitySource`

```ts
interface GravitySource
```

A point mass that pulls on bodies: where it is and how heavy (see `gravityAccel`).

- `x: number` — The world x position of the source.
- `y: number` — The world y position of the source.
- `mass: number` — The mass of the source. Scales the pull.

### `MotionOptions`

```ts
interface MotionOptions
```

Per-frame inputs to `integrateMotion`.

- `delta: number` — Frame time in seconds.
- `accel?: Vec2` — Summed acceleration this frame (thrust + any extra pulls).
- `gravity?: Vec2` — Optional constant gravity vector (added to accel).
- `drag?: number` — Per-second linear drag coefficient (0/undefined = none).
- `maxSpeed?: number` — Terminal-speed clamp (undefined = uncapped).

### `Vec2`

```ts
interface Vec2
```

A 2D point or vector. Plain data, so anything can produce one.

- `x: number` — Horizontal position or component, in world units; +x is right.
- `y: number` — Vertical position or component, in world units; +y is down.

### `VecMotionApi`

```ts
type VecMotionApi = typeof kit
```

`game.vecMotion` — every function this pack carries, as one namespace.

### `VecPt`

```ts
type VecPt = Vec2
```

A point on a path — the same shape, named for what it is used as.

---

## For AI agents: Phaser AE

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