# `GlyphsCallback processFont:instance:supporting:error:`

*Instance Method*

Is called to process a font before output

## Declaration

```swift
func processFont(_ font: GSFont, instance: GSInstance, supporting supportedFeatures: GSDrawStackFeature) throws
```

```objc
- (BOOL) processFont:(GSFont *) font instance:(GSInstance *) instance supporting:(GSDrawStackFeature) supportedFeatures error:(NSError **) error;
```

```python
processFont_instance_supporting_error_(font: GSFont, instance: GSInstance, supportedFeatures: GSDrawStackFeature) -> tuple[bool, NSError]
```

## Parameters

- `font` — The glyph 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