---
title: indexBuffer
framework: metal
role: symbol
role_heading: Instance Property
path: metal/mtl4accelerationstructuremotioncurvegeometrydescriptor/indexbuffer
---

# indexBuffer

Assigns an optional index buffer containing references to control points in the control point buffers.

## Declaration

```swift
var indexBuffer: MTL4BufferRange { get set }
```

## Discussion

Discussion All keyframes share the same index buffer, with each index representing the first control point of a curve segment. You are responsible for ensuring the buffer address of the range is not zero.