---
title: "rotate(by:)"
framework: coregraphics
role: symbol
role_heading: Instance Method
path: "coregraphics/cgcontext/rotate(by:)"
---

# rotate(by:)

Rotates the user coordinate system in a context.

## Declaration

```swift
func rotate(by angle: CGFloat)
```

## Parameters

- `angle`: The angle, in radians, by which to rotate the coordinate space of the specified context. Positive values rotate counterclockwise and negative values rotate clockwise.)

## Discussion

Discussion The direction that the context is rotated may appear to be altered by the state of the current transformation matrix prior to executing this function. For example, on iOS, a UIView applies a transformation to the graphics context that inverts the Y-axis (by multiplying it by -1). Rotating the user coordinate system on coordinate system that was previously flipped results in a rotation in the opposite direction (that is, positive values appear to rotate the coordinate system in the clockwise direction).

## See Also

### Working with the Current Transformation Matrix

- [ctm](coregraphics/cgcontext/ctm.md)
- [scaleBy(x:y:)](coregraphics/cgcontext/scaleby(x:y:).md)
- [translateBy(x:y:)](coregraphics/cgcontext/translateby(x:y:).md)
- [concatenate(_:)](coregraphics/cgcontext/concatenate(_:).md)