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How to use UIBezierPath and CGPath in SwiftUI

Paul Hudson    @twostraws   

Fully updated for Xcode 11.1

If you have existing paths made using UIBezierPath or CGPath it’s trivial to convert them for use in SwiftUI because the Path struct has an initializer directly from CGPath.

Note: UIBezierPath is not available in macOS, so if you’re trying to keep your SwiftUI code cross platform you should migrate to CGPath instead.

As an example, here’s a UIBezierPath extension I made to store the logo for an app I built, called Unwrap:

extension UIBezierPath {
    /// The Unwrap logo as a Bezier path.
    static var logo: UIBezierPath {
        let path = UIBezierPath()
        path.move(to: CGPoint(x: 0.534, y: 0.5816))
        path.addCurve(to: CGPoint(x: 0.1877, y: 0.088), controlPoint1: CGPoint(x: 0.534, y: 0.5816), controlPoint2: CGPoint(x: 0.2529, y: 0.4205))
        path.addCurve(to: CGPoint(x: 0.9728, y: 0.8259), controlPoint1: CGPoint(x: 0.4922, y: 0.4949), controlPoint2: CGPoint(x: 1.0968, y: 0.4148))
        path.addCurve(to: CGPoint(x: 0.0397, y: 0.5431), controlPoint1: CGPoint(x: 0.7118, y: 0.5248), controlPoint2: CGPoint(x: 0.3329, y: 0.7442))
        path.addCurve(to: CGPoint(x: 0.6211, y: 0.0279), controlPoint1: CGPoint(x: 0.508, y: 1.1956), controlPoint2: CGPoint(x: 1.3042, y: 0.5345))
        path.addCurve(to: CGPoint(x: 0.6904, y: 0.3615), controlPoint1: CGPoint(x: 0.7282, y: 0.2481), controlPoint2: CGPoint(x: 0.6904, y: 0.3615))
        return path
    }
}

That uses control points that are normalized to the range of 0 through 1, so that I can render it inside any kind of container and just scale it up to fit the available space.

In SwiftUI that would mean creating a transform that scales the Bezier path up by the minimum of either the width or the height, then applying that to a path, like this:

struct ScaledBezier: Shape {
    let bezierPath: UIBezierPath

    func path(in rect: CGRect) -> Path {
        let path = Path(bezierPath.cgPath)

        // Figure out how much bigger we need to make our path in order for it to fill the available space without clipping.
        let multiplier = min(rect.width, rect.height)

        // Create an affine transform that uses the multiplier for both dimensions equally.
        let transform = CGAffineTransform(scaleX: multiplier, y: multiplier)

        // Apply that scale and send back the result.
        return path.applying(transform)
    }
}

With all that in place, we can now render any kind of Bezier path we want:

struct ContentView: View {
    var body: some View {
        ScaledBezier(bezierPath: .logo)
            .stroke(lineWidth: 2)
            .frame(width: 200, height: 200)
    }
}

If you’re starting with a CGPath rather than a UIBezierPath, things are even easier. This line:

let path = Path(bezierPath.cgPath)

Becomes this:

let path = Path(yourCGPath)

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