# `CGBlendModeFromGSCompositingOperation`

*Function*

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

## Declaration

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

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

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

## See Also

### Compositing

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