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How to draw a custom path

Paul Hudson    @twostraws   

Fully updated for Xcode 11.1

SwiftUI lets us draw custom paths by conforming to the Path protocol, so we can create our own shapes that work the same as Rectangle, Capsule, and Circle. Conforming to this protocol isn’t hard, because all you need to do is support a path(in:) method that accepts a CGRect and returns a Path. Even better, you can use any paths you’ve previously built using CGPathorUIBezierPath`, then convert the result to a SwiftUI path.

Note: The code below uses SwiftUI’s native path drawing API, but this is broken in beta 5 – your code will compile but crash at runtime. Apple has said this ought to be fixed in beta 6.

If you want to use SwiftUI’s native Path type, create a variable instance of it then add as many points as you need. Don’t think about colors, fills, or stroke widths – you’re focusing on the raw shape here, and those kinds of settings are provided when your custom path is used.

For example, we could make a creative effect by drawing a series of rotated squares with something like this:

struct SpiroSquare: Shape {
    func path(in rect: CGRect) -> Path {
        var path = Path()

        let rotations = 5
        let amount = .pi / CGFloat(rotations)
        let transform = CGAffineTransform(rotationAngle: amount)

        for _ in 0 ..< rotations {
            path = path.applying(transform)

            path.addRect(CGRect(x: -rect.width / 2, y: -rect.height / 2, width: rect.width, height: rect.height))
        }

        return path
    }
}

You could then use it inside a view like this:

struct ContentView: View {
    var body: some View {
        SpiroSquare()
            .stroke()
            .frame(width: 200, height: 200)
    }
}

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