# WaterWakeFeed

> Talos next · Since next

What a script tells the water effects about its hull ({@link EntityHandle.setWaterWake}).

A field left out is left to the engine.

## Signature

```ts
export interface WaterWakeFeed {
  /** How hard its thrust pushes, 0..1: it churns the trail behind the stern. */
  thrust?: number
  /** How far onto the plane it is, 0..1: it churns the trail, and holds the wake while the hull skips. */
  planing?: number
  /** How much of the hull is in the water, 0..1. */
  immersion?: number
  /** Where its thrust goes into the water, a point on the entity, metres: a jet's plume starts here. */
  thrustAt?: Vec3
  /** Its bow, a point on the entity, metres: the bow's spray starts under it. */
  bow?: Vec3
}
```

Import: `import type { WaterWakeFeed } from "@argus/api"`

## Members

| Member | Signature | Description |
|---|---|---|
| `thrust` | `thrust?: number` | How hard its thrust pushes, 0..1: it churns the trail behind the stern. |
| `planing` | `planing?: number` | How far onto the plane it is, 0..1: it churns the trail, and holds the wake while the hull skips. |
| `immersion` | `immersion?: number` | How much of the hull is in the water, 0..1. |
| `thrustAt` | `thrustAt?: Vec3` | Where its thrust goes into the water, a point on the entity, metres: a jet's plume starts here. |
| `bow` | `bow?: Vec3` | Its bow, a point on the entity, metres: the bow's spray starts under it. |

## Example

The tested fixture `fixtures/host/hover.ts`.

```ts
import type { Behavior, Ctx, Vec3 } from "@argus/api"
// docs/API.md, "Forces, torques and impulses": a body that hovers (thrust = m·g), and the same lift
// as four rotors in the airframe's own frame plus a yaw torque. Typechecked by packages/api's tests.
const HUBS: Vec3[] = [[0.3, 0, 0.3], [-0.3, 0, 0.3], [0.3, 0, -0.3], [-0.3, 0, -0.3]]

function hover(ctx: Ctx) {
  const body = ctx.body
  if (!body) return
  if (ctx.props["rotors"] !== true) {
    body.addForce([0, body.mass * 9.81, 0])
    return
  }
  for (const h of HUBS) body.addForceAtPoint([0, (body.mass * 9.81) / 4, 0], h, "local")
  body.addTorque([0, (ctx.props["yaw"] as number | undefined) ?? 0, 0], "local")
}

export default {
  // The first physics step runs before the first update; this is its thrust.
  init(ctx) { hover(ctx) },
  update(ctx) { hover(ctx) },
} satisfies Behavior
```