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

# accelerationStructureIndex

The index of an acceleration structure which applies to the next acceleration-structure motion instance you create with the descriptor.

## Declaration

```swift
var accelerationStructureIndex: UInt32
```

## Discussion

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

## See Also

### Related Documentation

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