SwiftUI Shape that will be a capsule up to a maximum corner radius. Useful for capsule UI that should adapt to a rounded rect past a certain scale.

AdaptiveCapsule.swift

//
//  AdaptiveCapsule.swift
//  Design
//
//  Created by Kyle Bashour on 8/21/25.
//

import SwiftUI

/// Will draw as a capsule up to a maximum corner radius, after which it draws as a rounded rect.
public struct AdaptiveCapsule: InsettableShape {
    public var maximumCornerRadius: CGFloat?
    public var style: RoundedCornerStyle

    private var insetAmount: CGFloat = 0

    public init(maximumCornerRadius: CGFloat? = nil, style: RoundedCornerStyle = .continuous) {
        self.maximumCornerRadius = maximumCornerRadius
        self.style = style
    }

    public func path(in rect: CGRect) -> Path {
        let insetRect = rect.insetBy(dx: insetAmount, dy: insetAmount)
        var cornerRadius = min(insetRect.width, insetRect.height) / 2

        if let maximumCornerRadius {
            let insetMaximumCornerRadius = maximumCornerRadius - insetAmount
            cornerRadius = min(insetMaximumCornerRadius, cornerRadius)
        }

        return Path(roundedRect: insetRect, cornerRadius: cornerRadius, style: style)
    }

    public func inset(by amount: CGFloat) -> AdaptiveCapsule {
        var copy = self
        copy.insetAmount += amount
        return copy
    }
}

#Preview {
    VStack {
        ZStack {
            RoundedRectangle(cornerRadius: 40)
            RoundedRectangle(cornerRadius: 40)
                .inset(by: 20)
            Text("RoundedRectangle")
                .foregroundStyle(.black)
        }

        ZStack {
            AdaptiveCapsule(maximumCornerRadius: 40)
            AdaptiveCapsule(maximumCornerRadius: 40)
                .inset(by: 20)
            Text("Matches RoundedRectangle Insetting")
                .foregroundStyle(.black)
        }

        ZStack {
            AdaptiveCapsule(maximumCornerRadius: nil)
            AdaptiveCapsule(maximumCornerRadius: nil)
                .inset(by: 20)
            Text("Capsule Behavior")
                .foregroundStyle(.black)
        }

        VStack {
            HStack {
                AdaptiveCapsule(maximumCornerRadius: nil)
                AdaptiveCapsule(maximumCornerRadius: nil)
                AdaptiveCapsule(maximumCornerRadius: nil)
                AdaptiveCapsule(maximumCornerRadius: nil)
                AdaptiveCapsule(maximumCornerRadius: nil)
            }

            Text("Vertical Capsules")
                .foregroundStyle(.black)
        }
    }
    .padding()
    .foregroundStyle(.blue.opacity(0.5))
}