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# bounds

The bounding box to encompass all of the instances this group part draws.

```
var bounds: BoundingBox?
```

## Discussion

If bounds is `nil`, RealityKit calculates a bounding box for you each time you
update your instances within [`LowLevelInstanceData`](/documentation/RealityKit/LowLevelInstanceData).

Automatic bounds calculation is not supported when [`LowLevelInstanceData`](/documentation/RealityKit/LowLevelInstanceData)
is updated via [`replace(using:)`](/documentation/RealityKit/LowLevelInstanceData/replace(using:)).
Provide a non-nil bounds value when updating instances with Metal.

---

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