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# MTLStepFunction

The frequency and locations at which a function fetches attribute data.

```
enum MTLStepFunction
```

## Topics

### Step options

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

The function fetches attribute data once.

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

The function fetches data based on the instance index.

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

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

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

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

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

The vertex function fetches data for every vertex.

[`MTLStepFunction.threadPositionInGridX`](/documentation/Metal/MTLStepFunction/threadPositionInGridX)

The compute function fetches data based on the thread’s `x` coordinate.

[`MTLStepFunction.threadPositionInGridY`](/documentation/Metal/MTLStepFunction/threadPositionInGridY)

The compute function fetches data based on the thread’s `y` coordinate.

[`MTLStepFunction.threadPositionInGridXIndexed`](/documentation/Metal/MTLStepFunction/threadPositionInGridXIndexed)

The compute function fetches data by using the thread’s `x` coordinate to look up a value in the index buffer.

[`MTLStepFunction.threadPositionInGridYIndexed`](/documentation/Metal/MTLStepFunction/threadPositionInGridYIndexed)

The compute function fetches data by using the thread’s `y` coordinate to look up a value in the index buffer.


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