---
title: "Underwater: API"
package: "@phaser-ae/underwater-3d"
tier: Pro
version: 3.0.0-2
released: 2026-10-14
updated: 2026-10-19
description: "The view from below the surface of a 3D sea, with colour lost to distance, a clean waterline, caustics on the seabed, shafts of sunlight and the water's own fog."
url: https://phaser.io/packs/underwater-3d/api
site: Phaser - https://phaser.io
---

# Underwater: API

`@phaser-ae/underwater-3d` — Being under the water: per-channel extinction against the scene depth, four named waters, a ray-based waterline, caustics, light shafts and fog.

## The pack

### `underwater3d`

```ts
function underwater3d(opts: Underwater3dOptions = {}): Pack<{ underwater: Underwater3dApi }>
```

The `underwater-3d` pack: a full-screen pass that runs only while the eye is below the surface.
Requires a 3D world, `render-3d` (its scene depth and lighting record) and a WebGPU or WebGL2 backend; pair it
with `water-3d` so waves overhead decide where the waterline actually is. Throws on an unknown `preset` or a
`waterColor` that is not a css colour.

## Helpers

### `absorb`

```ts
function absorb(sigma: readonly [number, number, number], dist: number): Sigma
```

Per-channel Beer–Lambert transmittance, `exp(−σ · distance)` — the CPU twin of the shader's law.

### `bakeCausticField`

```ts
function bakeCausticField(size = 256, t = 1.0): Float32Array
```

One Hoskins caustic field, `size`×`size` texels over one tile, row-major. Values are the raw pattern —
mostly 0..1 with sparkle peaks above 1. Pure and deterministic; `t` picks the phase slice to bake.

### `submersionState`

```ts
function submersionState(prev: boolean, camY: number, surfY: number, hysteresis: number): { submerged: boolean; depth: number }
```

The submersion decision, with HYSTERESIS: the camera has to cross `hysteresis` BEYOND the surface line to
flip state, so a hull bobbing exactly at the waterline never strobes the whole effect on and off. `depth` is
how far the camera sits below the surface, and 0 above it.

### `UNDERWATER_PRESETS`

```ts
const UNDERWATER_PRESETS: Record<string, UnderwaterPreset>
```

The named waters. These are BRIGHT BY DEFAULT on purpose: triplets taken from physical tables kill red in
about five metres, which is correct and reads as instant murk in a game — the stylised reef shots everyone
pictures have almost no view extinction at all. `murk` is the one that keeps the heavy physical feel.

### `underwaterFog`

```ts
function underwaterFog( opts: { waterColor: string; sunSigma: Sigma; sigma: Sigma; maxView: number }, depth: number, storm = 0, ): { color: string; near: number; far: number }
```

The gentle base tint every OTHER 3D shader gets for free: the water colour, darkened with depth by the
downwelling law and desaturated toward grey-green by storm, over a fog band that closes in with σ.

The composite owns the per-channel extinction; this only has to make the murk, the translucents, the beams
and the particles agree with the underwater look — otherwise they float in front of it as if dry.

## Functions

### `createCausticTexture`

```ts
function createCausticTexture(device: GPUDevice, size = 256): GPUTexture
```

Bake the field into an `rg8unorm` texture with a full 2×2-box mip chain. TWO INDEPENDENT PHASES, one
per channel: the surface shader min-blends a tap of R with a tap of G, so no repeating motif can line
up with itself — two taps of ONE field at related scales tile visibly. The texel stores value/2 so the
above-1 sparkle peaks survive quantisation, and the shader multiplies the tap by 2 to undo it.

## Types

### `Sigma`

```ts
type Sigma = [number, number, number]
```

A per-channel extinction triplet, in inverse world units.

### `Underwater3dApi`

```ts
interface Underwater3dApi
```

`game.underwater`.

- `diagnostics(): { active: boolean; submerged: boolean; depth: number; fullUnder: number; shallowK: number; surfaceY: number; sigma: Sigma; viewSigma: Sigma; sunSigma: Sigma; waterColor: string; maxView: number; fog: { color: string; near: number; far: number }; rayStrength: number }` — Optical values used by the composite at the current camera position, suitable for CPU ray diagnostics.
- `rayStrength: number` — Additional shaft brightness multiplier, independent of the on/off ray control. Default 1.
- `sigma: Sigma` — Per-channel view extinction. Replace the tuple to retune absorption live.
- `grade: number` — Underwater colour grading strength, 0..1.
- `causticTile: number` — World units per caustic tile.
- `causticSpeed: number` — Caustic animation speed.
- `rayBand: number` — Clearance below the surface at which light shafts begin.
- `rayGap: number` — Arc spacing between light shafts, world units.
- `level: number` — Sea level.
- `clarity: number` — Master clarity, 0..1.
- `caustics: number` — Caustic brightness.
- `wobble: number` — Screen wobble.
- `vignette: number` — Soft screen vignette.
- `storm: number` — Storm dial, 0..1.
- `enabled: boolean` — Turn it off entirely.
- `rays: number` — The bars of sunlight hanging under the surface, 0 for none. Default 1.
- `rayFlicker: number` — How deeply each beam dips as it flickers, 0 for steady. Default 1.
- `rayNear: number` — How far the wall of beams stands from the camera, world units. Default 14.
- `groundAt(fn: ((x: number, z: number) => number) | null): void` — Give the beams a seabed so each is capped above it and shortens smoothly in the shallows.
- `setPreset(name: string): void` — Swap the water live: `'reef'`, `'ocean'`, `'pool'`, `'murk'`. Throws on any other name.
- `shaftMod(): { atten: number; tint: [number, number, number] } | null` — How the SURFACE god rays should be modulated while the eye is under: the downwelling transmittance to this depth, and the water's own hue. Null when dry, or when rays are off. `god-rays-3d` reads it, so shafts from the sun die with depth and go green rather than hanging in the water at full brightness.
- `readonly submerged: boolean` — Is the camera under the surface right now? Hysteresis keeps this from flickering at the line.
- `readonly depth: number` — How deep the camera is, or 0 above.
- `surfaceAt(fn: ((x: number, z: number) => number) | null): void` — Give it a moving surface — `water-3d`'s `heightAt` — so waves overhead decide where the line is.

### `Underwater3dOptions`

```ts
interface Underwater3dOptions
```

How the water looks from inside it. Anything left unset comes from the preset.

- `preset?: string` — `'reef'` (the default), `'ocean'`, `'pool'` or `'murk'`; any other name throws.
- `level?: number` — Sea level; the effect is on below it. Default 0.
- `sigma?: Sigma` — Per-channel view extinction — how fast the murk closes in.
- `sunSigma?: Sigma` — Per-channel downwelling extinction — how fast light from above dies with depth.
- `waterColor?: string` — The in-scatter murk colour: any css colour the kernel reads (`#2f9fc4`, `rgb(47, 159, 196)`, `cyan`); anything else throws.
- `maxView?: number` — Roughly how far you can see, world units.
- `clarity?: number` — Master CLARITY, 0..1: 1 is the water as authored, 0 is crystal clear. Default 1.
- `caustics?: number` — Caustic brightness, 0..1.
- `causticTile?: number` — World units per caustic tile. Default 6.
- `causticFade?: number` — Receiver depth at which caustics fade to nothing. Default 20.
- `causticSpeed?: number` — How fast caustics crawl. Default 1.
- `wobble?: number` — Screen wobble in uv; kept small on purpose. Default 0.002.
- `vignette?: number` — Soft screen vignette, 0..1.
- `meniscus?: number` — How bright the meniscus band at the crossing is. Default 0.35.
- `hysteresis?: number` — How far the camera must cross the line to flip state — this is what stops it strobing. Default 0.06.
- `storm?: number` — Storm dial 0..1: desaturates the murk toward grey-green and closes it in. Default 0.
- `rays?: number` — The bars of sunlight hanging under the surface, 0 for none. Default 1.
- `rayFlicker?: number` — How deeply each beam dips as it flickers, 0 for steady. Default 1.
- `rayNear?: number` — How far the wall of beams stands from the camera. Default 14.
- `rayBand?: number` — How far below the flat surface a beam starts, clearing the ripples. Default 1.2.
- `rayGap?: number` — Arc gap between beams; smaller is a denser wall. Default 12.
- `driveFog?: boolean` — Drive the scene's fog from the water while submerged. Default true.
- `enabled?: boolean` — Whether the pass runs at all. Default true.

### `UnderwaterPreset`

```ts
interface UnderwaterPreset
```

One named water: how fast each channel dies, what colour the murk is, and how the screen is graded.

- `sigma: Sigma` — View extinction — how fast the murk closes in on what you are looking at.
- `sunSigma: Sigma` — Downwelling extinction — how fast the light from above dies with depth.
- `waterColor: string` — The in-scatter murk colour, css.
- `maxView: number` — Roughly how far you can see, world units.
- `caustics: number` — Caustic brightness for this water.
- `vignette: number` — The soft screen vignette, 0..1.
- `grade: number` — The depth grade, 0..1.

---

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