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# refit

An option that lets you update an acceleration structure after creating it.

```
static var refit: MTLAccelerationStructureUsage { get }
```

## Discussion

Apply this option to make a modifiable acceleration structure, which you can update over time,
such as for geometry changes.
By default, the framework builds immutable acceleration structures for performance.
When you apply the [`refit`](/documentation/Metal/MTLAccelerationStructureUsage/refit) option, the framework builds an acceleration structure more conservatively,
which can reduce its intersection performance.

> Note:
> Refitting an acceleration structure generally works better when the geometry changes are relatively small.

---

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