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# stencilCompareFunction

The comparison that is performed between the masked reference value and a masked value in the stencil attachment.

```
var stencilCompareFunction: MTLCompareFunction { get set }
```

## Discussion

For example, if `stencilCompareFunction` is [`MTLCompareFunction.less`](/documentation/Metal/MTLCompareFunction/less), then the stencil test passes if the masked reference value is less than the masked stored stencil value. The default value is [`MTLCompareFunction.always`](/documentation/Metal/MTLCompareFunction/always), which indicates that the stencil test always passes.

The stored stencil value and the reference value are both *masked* by performing a logical AND operation with the [`readMask`](/documentation/Metal/MTLStencilDescriptor/readMask) value before the comparison takes place. For more information on possible values, see [`MTLCompareFunction`](/documentation/Metal/MTLCompareFunction).

## See Also

[`setStencilReferenceValue(_:)`](/documentation/Metal/MTLRenderCommandEncoder/setStencilReferenceValue(_:))

Configures the same comparison value for front- and back-facing primitives.


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