---
title: accelerationStructureIndex
framework: metal
role: symbol
role_heading: Instance Property
path: metal/mtlaccelerationstructureuseridinstancedescriptor/accelerationstructureindex
---

# accelerationStructureIndex

The index of the acceleration structure to use for the instance.

## Declaration

```swift
var accelerationStructureIndex: UInt32
```

## Discussion

Discussion This index refers to a bottom-level instance in the instancedAccelerationStructures of the MTLInstanceAccelerationStructureDescriptor that you use to create the new instance acceleration structure.

## See Also

### Related Documentation

- [instancedAccelerationStructures](metal/mtlinstanceaccelerationstructuredescriptor/instancedaccelerationstructures.md)