---
title: "Vector Hit Tests: API"
package: "@phaser-ae/vector-hit"
tier: Free
version: 3.0.0-3
released: 2026-10-14
updated: 2026-10-20
description: "The collision and picking maths of a line-art game, from point-in-outline and distance to a stroke to swept anti-tunnelling tests and bounce and friction response."
url: https://phaser.io/packs/vector-hit/api
site: Phaser - https://phaser.io
---

# Vector Hit Tests: API

`@phaser-ae/vector-hit` — Did it touch, where, and what happens next: point-in-outline, distance to a stroke, swept tests and surface response.

## The pack

### `vectorHit`

```ts
function vectorHit(): Pack<{ vecHit: VecHitApi }>
```

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

## Helpers

### `arcHit`

```ts
function arcHit( cx: number, cy: number, r: number, from: number, to: number, px: number, py: number, tol = 6, ): boolean
```

Is `(px, py)` ON an arc — within `tol` of the radius AND inside the sweep?

The hit test segmented rings need: a shot only kills the shield section it
actually crossed. Test in the ring's LOCAL space — subtract the centre and
rotate the point by `-ring.rot` first, so a spinning ring needs no
per-section bookkeeping.

### `circleHit`

```ts
function circleHit(aPos: Vec2, aRadius: number, bPos: Vec2, bRadius: number): boolean
```

Cheap bounding-circle overlap — the pragmatic default hit test for vector games.

### `distToPath`

```ts
function distToPath(px: number, py: number, pts: readonly VecPt[], closed = false): number
```

Shortest distance from `(px, py)` to the path — the test a STROKE needs.

An open polyline has no interior, so "did I click the line" is a proximity
question, not a containment one. Closed paths include the closing edge.

Returns `Infinity` for an empty path and 0 for a single point at `(px, py)`.

### `pointInPath`

```ts
function pointInPath(px: number, py: number, pts: readonly VecPt[]): boolean
```

Is `(px, py)` INSIDE the closed path `pts`? Even-odd ray crossing.

Correct for concave outlines and self-intersections, which matters here
because `generatePolygon` produces exactly that — a lumpy asteroid is not
convex and a convex-hull test would grab empty space beside it.

The path is treated as closed whether or not the last point repeats the
first: the `j = i++` walk always includes the closing edge.

### `pointInPolygon`

```ts
function pointInPolygon(point: Vec2, worldPoly: Vec2[]): boolean
```

Ray-casting (even-odd) point-in-polygon test. `worldPoly` MUST be in world
space — call `transformVerts` first. Handles convex AND concave simple
polygons of either winding.

### `polylineSegments`

```ts
function polylineSegments(points: Vec2[]): Segment[]
```

Turn a terrain polyline (or any open path) into wall segments for `sweepVsSegments`.

### `resolveSurface`

```ts
function resolveSurface(vel: Vec2, normal: Vec2, opts: SurfaceResponse = {}): Vec2
```

The general surface-collision response. Splits the velocity into normal and
tangential parts against the outward unit `normal`: the normal part bounces
back scaled by `restitution`; the tangential part is scaled by (1 - `friction`).
`bounceThreshold` suppresses the bounce below a minimum approach speed so a
resting body settles instead of jittering.

### `surfaceFriction`

```ts
function surfaceFriction( vel: Vec2, normal: Vec2, coefficient: number, dt: number, gravityDir: Vec2 = { x: 0, y: 1 }, ): Vec2
```

Continuous ground friction for a grounded body — damps the velocity ALONG the
surface, scaled by how flat it is (≈ cos of the slope): full on flat ground,
less on a steep slope, none on a wall. Call each frame while grounded.

### `sweepVsSegments`

```ts
function sweepVsSegments(prev: Vec2, cur: Vec2, segments: Segment[]): SweepHit | null
```

Sweep a moving point's path (prev → cur) against static wall segments and return
the EARLIEST contact, or null. The core anti-tunnel test for bodies vs line
geometry (terrain, cave walls).

## Functions

### `segmentIntersection`

```ts
function segmentIntersection(p1: Vec2, p2: Vec2, p3: Vec2, p4: Vec2): Vec2 | null
```

Intersection point of segment p1→p2 with segment p3→p4, or null if they don't cross within both spans.

## Types

### `Segment`

```ts
interface Segment
```

A wall segment from `a` to `b` — terrain pieces, cave walls, arena edges.

- `a: Vec2` — The start point of the wall segment.
- `b: Vec2` — The end point of the wall segment.

### `SurfaceResponse`

```ts
interface SurfaceResponse
```

Tuning for `resolveSurface` — how a body bounces, scrubs, and settles on contact.

- `restitution?: number` — 0 = no bounce (pure slide), 1 = full elastic bounce. Default 0.
- `friction?: number` — 0 = frictionless, 1 = grip (kills tangential speed on contact). Default 0.
- `bounceThreshold?: number` — Only bounce if the approach speed exceeds this — below it the body SETTLES. Default 0.

### `SweepHit`

```ts
interface SweepHit
```

The earliest contact a swept point made: where, which segment, how far along the path (0..1).

- `point: Vec2` — The contact point, in world units.
- `index: number` — The index of the segment that was hit.
- `t: number` — How far along the swept path the contact is, 0..1.

### `Vec2`

```ts
interface Vec2
```

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

- `x: number` — Horizontal coordinate in world units; grows to the right.
- `y: number` — Vertical coordinate in world units; grows downwards (the 2D world is Y-down).

### `VecHitApi`

```ts
type VecHitApi = typeof kit
```

`game.vecHit` — 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.

---

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