---
title: motionStartBorderMode
framework: metal
role: symbol
role_heading: Instance Property
path: metal/mtl4primitiveaccelerationstructuredescriptor/motionstartbordermode
---

# motionStartBorderMode

Configures the behavior when the ray-tracing system samples the acceleration structure before the motion start time.

## Declaration

```swift
var motionStartBorderMode: MTLMotionBorderMode { get set }
```

## Discussion

Discussion Use this property to control the behavior when the ray-tracing system samples the acceleration structure at a time prior to the one you set for motionStartTime. The default value of this property is MTLMotionBorderModeClamp.