# `GlyphsCallback processLayer:instance:error:`

*Instance Method*

Is called to process a layer before output

## Declaration

```swift
func processLayer(_ layer: GSLayer, instance: GSInstance) throws
```

```objc
- (BOOL) processLayer:(GSLayer *) layer instance:(GSInstance *) instance error:(NSError **) error;
```

```python
processLayer_instance_error_(layer: GSLayer, instance: GSInstance) -> tuple[bool, NSError]
```

## Parameters

- `layer` — The layer to process
- `instance` — The exported instance
- `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