# `GlyphsCallback processLayer:supporting:extraHandles:error:`

*Instance Method*

Is called to process the layer preparing it for preview

## Declaration

```swift
func processLayer(_ layer: GSLayer, supporting supportedFeatures: GSDrawStackFeature, extraHandles: NSMutableArray?) throws
```

```objc
- (BOOL) processLayer:(GSLayer *) layer supporting:(GSDrawStackFeature) supportedFeatures extraHandles:(NSMutableArray *) extraHandles error:(NSError **) error;
```

```python
processLayer_supporting_extraHandles_error_(layer: GSLayer, supportedFeatures: GSDrawStackFeature, extraHandles: list) -> tuple[bool, NSError]
```

## Parameters

- `layer` — The layer to process
- `extraHandles` — On return, a list of GSHandle objects that are shown as small black dots in the UI
- `error` — On output, a pointer to an error object that describes why the method failed, or `nil` if no error occurred. If you are not interested in the error information, pass `nil` for this parameter.

## Return Value

NO if there was an error