---
title: motionTransformsStartIndex
framework: metal
role: symbol
role_heading: Instance Property
path: metal/mtlaccelerationstructuremotioninstancedescriptor/motiontransformsstartindex
---

# motionTransformsStartIndex

The index of motion data that represents the first key-frame motion data, which applies to the next acceleration-structure motion instance you create with the descriptor.

## Declaration

```swift
var motionTransformsStartIndex: UInt32
```

## Discussion

Discussion The index points to an entry in an MTLInstanceAccelerationStructureDescriptor instance’s transform data, which it stores in its motionTransformBuffer property.

## See Also

### Specifying motion data

- [motionStartTime](metal/mtlaccelerationstructuremotioninstancedescriptor/motionstarttime.md)
- [motionEndTime](metal/mtlaccelerationstructuremotioninstancedescriptor/motionendtime.md)
- [motionStartBorderMode](metal/mtlaccelerationstructuremotioninstancedescriptor/motionstartbordermode.md)
- [motionEndBorderMode](metal/mtlaccelerationstructuremotioninstancedescriptor/motionendbordermode.md)
- [motionTransformsCount](metal/mtlaccelerationstructuremotioninstancedescriptor/motiontransformscount.md)