SwiftUIで一部角丸の枠線を引く

MaskedCornerRoundedRectangle.swift

import SwiftUI

struct MaskedCornerRoundedRectangle: Shape {
    let topLeadingRadius: CGFloat
    let bottomLeadingRadius: CGFloat
    let bottomTrailingRadius: CGFloat
    let topTrailingRadius: CGFloat

    init(topLeadingRadius: CGFloat = 0, bottomLeadingRadius: CGFloat = 0, bottomTrailingRadius: CGFloat = 0, topTrailingRadius: CGFloat = 0) {
        self.topLeadingRadius = topLeadingRadius
        self.bottomLeadingRadius = bottomLeadingRadius
        self.bottomTrailingRadius = bottomTrailingRadius
        self.topTrailingRadius = topTrailingRadius
    }

    func path(in rect: CGRect) -> Path {
        Path { path in
            if topLeadingRadius > 0 {
                path.addArc(
                    center: CGPoint(x: rect.minX + topLeadingRadius, y: rect.minY + topLeadingRadius),
                    radius: topLeadingRadius,
                    startAngle: .degrees(180),
                    endAngle: .degrees(-90),
                    clockwise: false
                )
            } else {
                path.move(to: CGPoint(x: rect.minX, y: rect.minY))
            }

            if topTrailingRadius > 0 {
                path.addLine(to: CGPoint(x: rect.maxX - topTrailingRadius, y: rect.minY))
                path.addArc(
                    center: CGPoint(x: rect.maxX - topTrailingRadius, y: rect.minY + topTrailingRadius),
                    radius: topTrailingRadius,
                    startAngle: .degrees(-90),
                    endAngle: .degrees(0),
                    clockwise: false
                )
            } else {
                path.addLine(to: CGPoint(x: rect.maxX, y: rect.minY))
            }

            if bottomTrailingRadius > 0 {
                path.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY - bottomTrailingRadius))
                path.addArc(
                    center: CGPoint(x: rect.maxX - bottomTrailingRadius, y: rect.maxY - bottomTrailingRadius),
                    radius: bottomTrailingRadius,
                    startAngle: .degrees(0),
                    endAngle: .degrees(90),
                    clockwise: false
                )
            } else {
                path.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY))
            }

            if bottomLeadingRadius > 0 {
                path.addLine(to: CGPoint(x: rect.minX + bottomLeadingRadius, y: rect.maxY))
                path.addArc(
                    center: CGPoint(x: rect.minX + bottomLeadingRadius, y: rect.maxY - bottomLeadingRadius),
                    radius: bottomLeadingRadius,
                    startAngle: .degrees(90),
                    endAngle: .degrees(180),
                    clockwise: false
                )
            } else {
                path.addLine(to: CGPoint(x: rect.minX, y: rect.maxY))
            }

            path.closeSubpath()
        }
    }
}

Usage.swift

Color.red
	.overlay {
		MaskedCornerRoundedRectangle(topLeadingRadius: 8)
			.stroke(Color.blue, lineWidth: 1)
	}