# BusCollision

> Talos next · Since 0.6

Payload of the engine-published `"collision"` bus event.

Both sides are named rather than `other`, because {@link Behavior.onCollision} is called once per participant and its `other` is an answer only a participant can give. A subscriber to this is neither of them, so it gets `a` and `b` with their scene ids and decides for itself which one it cares about.

## Signature

```ts
export interface BusCollision {
  a: EntityHandle
  aId: string
  b: EntityHandle
  bId: string
  point: Vec3
  normal: Vec3
  impulse: number
}
```

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

## Members

| Member | Signature | Description |
|---|---|---|
| `a` | `a: EntityHandle` |  |
| `aId` | `aId: string` |  |
| `b` | `b: EntityHandle` |  |
| `bId` | `bId: string` |  |
| `point` | `point: Vec3` |  |
| `normal` | `normal: Vec3` |  |
| `impulse` | `impulse: number` |  |

## Example

The tested fixture `fixtures/app/agent.ts`.

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

// Sends a nav agent to `props.target` once, then reports arrival through ctx.state so the
// test can read it without polling the crowd directly.
export default {
  init(ctx) {
    ctx.state.arrived = false
    ctx.nav?.goTo(ctx.props.target as [number, number, number])
  },
  update(ctx) {
    if (ctx.nav?.arrived) ctx.state.arrived = true
  },
} satisfies Behavior
```