# RoadBarrier

> Talos next · Since 0.6

A road's wall as its file asked for it: `RoadLine.barrier`.

## Signature

```ts
export interface RoadBarrier {
  /** Which sides have a wall. */
  readonly sides: "left" | "right" | "both"
  /** Wall height above the road surface (along the banked up axis), metres. */
  readonly heightM: number
  /** Wall thickness, metres. */
  readonly thicknessM: number
  /** Gap between the kerb's outer edge and the wall's inner face, metres (floored over, so it is an apron a car can drive on). */
  readonly offsetM: number
  /** Ranges of distance `[from, to]` along the road with no wall. */
  readonly gapsAt: readonly (readonly [number, number])[]
}
```

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

## Members

| Member | Signature | Description |
|---|---|---|
| `sides` | `readonly sides: "left" \| "right" \| "both"` | Which sides have a wall. |
| `heightM` | `readonly heightM: number` | Wall height above the road surface (along the banked up axis), metres. |
| `thicknessM` | `readonly thicknessM: number` | Wall thickness, metres. |
| `offsetM` | `readonly offsetM: number` | Gap between the kerb's outer edge and the wall's inner face, metres (floored over, so it is an apron a car can drive on). |
| `gapsAt` | `readonly gapsAt: readonly (readonly [number, number])[]` | Ranges of distance `[from, to]` along the road with no wall. |

## Example

The tested fixture `fixtures/host/road-edges.ts`.

```ts
// A behavior that keeps a car inside the road's wall: what `ctx.world.road(id).edge(s)` is for.
import type { Behavior } from "@argus/api"

export default {
  update(ctx) {
    const road = ctx.world.road("track")
    if (road === null) return
    const here = road.closest(ctx.entity.position)
    const edge = road.edge(here.s)
    // Keep the car's centre a radius inside the wall's inner face, or the kerb's edge when there is no wall.
    const limit = (edge.barrier?.inner ?? edge.kerbOuter) - 0.8
    const over: number = Math.abs(here.offset) - limit
    const wallHeight: number | undefined = road.barrier?.heightM
    const sides: "left" | "right" | "both" | undefined = road.barrier?.sides
    const kerb: number = road.kerbWidth + road.kerbHeight
    ctx.state.over = [over, wallHeight, sides, kerb, edge.halfWidth, edge.barrier?.left, edge.barrier?.right, edge.barrier?.outer, edge.barrier?.height]
  },
} satisfies Behavior
```