example-polygon.swift

import SwiftUI

public struct Polygon: Shape {
    public let sides: Int
    public init(sides: Int) { self.sides = sides }
    public func path(in rect: CGRect) -> Path {
        let diameter = Double(min(rect.size.width, rect.size.height))
        let radius = diameter / 2.0
        let rad = Double.pi / 180.0
        let center = CGPoint(x: rect.size.width / 2.0, y: rect.size.height / 2.0)
        return Path { path in
            for i in 0 ..< sides {
                let angle = Double(i) * (360.0 / Double(sides)) * rad
                let a = center.x + CGFloat(sin(angle) * radius)
                let b = center.y + CGFloat(cos(angle) * radius)
                let point = CGPoint(x: a, y: -b + CGFloat(diameter))
                if i == 0 {
                    path.move(to: point)
                } else {
                    path.addLine(to: point)
                }
            }
            path.closeSubpath()
        }
    }
}

struct ContentView: View {
    @State var sides = 3
    
    var body: some View {
        VStack {
            Spacer()
            
            Polygon(sides: sides)
                .fill(Color.blue)
                .frame(width: 200, height: 200)
            
            Spacer()
            
            Stepper("Sides: \(sides)", value: $sides, in: 3...30)
                .frame(width: 180)
        }
        .padding(50)
    }
}