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# motionStartBorderMode

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

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

## 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`](/documentation/Metal/MTL4PrimitiveAccelerationStructureDescriptor/motionStartTime).

The default value of this property is `MTLMotionBorderModeClamp`.

---

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