# BusUiFocused

> Talos next · Since 0.7

Payload of the engine-published `"ui-focused"` event: focus moved on a screen — the arrow keys or the pad, Tab, a click on a focusable node, or the first focus a screen takes when it comes up.

Once per move, never for a frame where focus stayed put. Raised with `"ui-activated"` (same tick, same rules, `by` null), so it reaches {@link Behavior.onEvent} too. What a menu turns into a hover sound, a description panel or a preview, without polling: `ts ctx.events.on("ui-focused", (ev) => { if (ev.data.screen === "garage" && ev.data.id) ctx.ui.set("blurb", "text-key", `kart.${ev.data.id}`) }) ` {@link Ui.focused} answers the same question at any moment.

## Signature

```ts
export interface BusUiFocused {
  /** The qualified id `GET /ui` reports: `"garage:karts/swift"`. Null when focus left every node of the screen. */
  node: string | null
  /** The screen focus moved on: `"garage"`. */
  screen: string
  /** The author's own id: `"swift"`. Null with `node`. Match on this and `screen`. */
  id: string | null
}
```

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

## Members

| Member | Signature | Description |
|---|---|---|
| `node` | `node: string \| null` | The qualified id `GET /ui` reports: `"garage:karts/swift"`. Null when focus left every node of the screen. |
| `screen` | `screen: string` | The screen focus moved on: `"garage"`. |
| `id` | `id: string \| null` | The author's own id: `"swift"`. Null with `node`. Match on this and `screen`. |

## Example

The tested fixture `fixtures/recipes/jump-pad-and-elevator/scenes/behaviors/camera-zone.ts`.

```ts
import type { Behavior } from "@argus/api"

/**
 * A trigger volume that retunes the camera while the player is inside it.
 *
 * The engine has no camera-zone concept and needs none: a volume, a `trigger` component and this.
 * Here the player's behaviour owns the camera (it re-sends its params when the view is turned), so
 * the zone tells it what to change rather than calling `ctx.camera.set` itself. In a scene where
 * nothing else writes the camera, the zone can call `ctx.camera.set(kind, params)` directly.
 */
interface Props {
  /** `ctx.camera.set` params to merge in on the way in, and on the way out. */
  inside?: Record<string, unknown>
  outside?: Record<string, unknown>
}

export default {
  onTrigger(ctx, trigger) {
    const params = trigger.entering ? ctx.props.inside : ctx.props.outside
    if (params) ctx.events.emit("camera-zone", { target: trigger.other.id, params })
  },
} satisfies Behavior<Record<string, never>, Props>
```