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# MTLVertexStepFunction

The frequency with which the vertex function or post-tessellation vertex function fetches attribute data.

```
enum MTLVertexStepFunction
```

## Topics

### Step functions

[`MTLVertexStepFunction.constant`](/documentation/Metal/MTLVertexStepFunction/constant)

The vertex function fetches attribute data once and uses that data for every vertex.

[`MTLVertexStepFunction.perVertex`](/documentation/Metal/MTLVertexStepFunction/perVertex)

The vertex function fetches and uses new attribute data for every vertex.

[`MTLVertexStepFunction.perInstance`](/documentation/Metal/MTLVertexStepFunction/perInstance)

The vertex function regularly fetches new attribute data for a number of instances that is determined by `stepRate`.

[`MTLVertexStepFunction.perPatch`](/documentation/Metal/MTLVertexStepFunction/perPatch)

The post-tessellation vertex function fetches data based on the patch index of the patch.

[`MTLVertexStepFunction.perPatchControlPoint`](/documentation/Metal/MTLVertexStepFunction/perPatchControlPoint)

The post-tessellation vertex function fetches data based on the control-point indices associated with the patch.


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