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# startOfVertexSampleIndex

The index the Metal device object should use to store GPU counters when starting the render pass’s vertex stage.

```
var startOfVertexSampleIndex: Int { get set }
```

## Discussion

Specify [`MTLCounterDontSample`](/documentation/Metal/MTLCounterDontSample) if you don’t want to sample GPU counters at the start of the vertex stage. Otherwise, specify an index within the sample buffer where you want the GPU to write the sample data.

On devices that don’t support [`MTLCounterSamplingPoint.atStageBoundary`](/documentation/Metal/MTLCounterSamplingPoint/atStageBoundary) you need to set the value to [`MTLCounterDontSample`](/documentation/Metal/MTLCounterDontSample).

---

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