# `OTCompositeModeFromGSCompositingOperation`

*Function*

Returns `-1` for values not supported by `OTCompositeMode`.

## Declaration

```swift
func OTCompositeModeFromGSCompositingOperation(_ op: GSCompositingOperation!) -> Int32
```

```objc
int32_t OTCompositeModeFromGSCompositingOperation(GSCompositingOperation op);
```

```python
OTCompositeModeFromGSCompositingOperation(op: GSCompositingOperation) -> int
```

## See Also

### Compositing

- [`CGBlendModeFromGSCompositingOperation`](/Core/GlyphsCore/CGBlendModeFromGSCompositingOperation) — Returns `-1` for values not supported by `CGBlendMode`.