A CGPath extension for generating squircle (superellipse) paths. Adapted from the PaintCode blog (https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)

CGPath+squircle.swift

//
//  Copyright © 2024 Darren Ford. All rights reserved.
//
//  Adapted from the PaintCode blog: https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles
//
//  MIT license
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
//  documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
//  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
//  permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all copies or substantial
//  portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
//  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
//  OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
//  OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//  PaintCode License: -
//
//  Created by Matej Dunik on 11/12/13.
//  Copyright (c) 2013 PixelCut. All rights reserved except as below:
//  This code is provided as-is, without warranty of any kind. You may use it in your projects as you wish.
//

import Foundation
import CoreGraphics.CGPath

// Source: [PaintCode](https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)

extension CGPath {
   /// Create a superellipse (squircle) within the specified rect with a default corner radius
   /// - Parameters:
   ///   - rect: The superellipse rect
   ///   - cornerRadius: The corner radius
   /// - Returns: A path containing the superellipse
   ///
   /// Source: [PaintCode](https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)
   @inline(__always) static func squircle(in rect: CGRect) -> CGPath {
      Self.superellipse(in: rect, cornerRadius: min(rect.width, rect.height))
   }

   /// Create a superellipse (squircle) within the specified rect with a default corner radius
   /// - Parameters:
   ///   - rect: The superellipse rect
   /// - Returns: A path containing the superellipse
   ///
   /// Source: [PaintCode](https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)
   @inline(__always) static func superellipse(in rect: CGRect) -> CGPath {
      Self.superellipse(in: rect, cornerRadius: min(rect.width, rect.height))
   }

   /// Create a superellipse (squircle) within the specified rect
   /// - Parameters:
   ///   - rect: The squircle rect
   ///   - cornerRadius: The corner radius
   /// - Returns: A path containing the squircle
   ///
   /// Source: [PaintCode](https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)
   @inline(__always) static func squircle(in rect: CGRect, cornerRadius: CGFloat) -> CGPath {
      Self.superellipse(in: rect, cornerRadius: cornerRadius)
   }

   /// Create a superellipse (squircle) within the specified rect
   /// - Parameters:
   ///   - rect: The superellipse rect
   ///   - cornerRadius: The corner radius
   /// - Returns: A path containing the superellipse
   ///
   /// Source: [PaintCode](https://www.paintcodeapp.com/news/code-for-ios-7-rounded-rectangles)
   static func superellipse(in rect: CGRect, cornerRadius: CGFloat) -> CGPath {
      let limit: CGFloat = min(rect.size.width, rect.size.height) / 2 / 1.52866483
      let limitedRadius: CGFloat = min(cornerRadius, limit)

      @inline(__always) func topLeft(_ x: CGFloat, _ y: CGFloat) -> CGPoint {
         CGPoint(
            x: rect.origin.x + x * limitedRadius,
            y: rect.origin.y + y * limitedRadius
         )
      }

      @inline(__always) func topRight(_ x: CGFloat, _ y: CGFloat) -> CGPoint {
         CGPoint(
            x: rect.origin.x + rect.size.width - x * limitedRadius,
            y: rect.origin.y + y * limitedRadius
         )
      }

      @inline(__always) func bottomRight(_ x: CGFloat, _ y: CGFloat) -> CGPoint {
         CGPoint(
            x: rect.origin.x + rect.size.width - x * limitedRadius,
            y: rect.origin.y + rect.size.height - y * limitedRadius
         )
      }

      @inline(__always) func bottomLeft(_ x: CGFloat, _ y: CGFloat) -> CGPoint {
         CGPoint(
            x: rect.origin.x + x * limitedRadius,
            y: rect.origin.y + rect.size.height - y * limitedRadius
         )
      }

      let path = CGMutablePath()
      path.move(to: topLeft(1.52866483, 0.00000000))
      path.addLine(to: topRight(1.52866471, 0.00000000))
      path.addCurve(
         to: topRight(0.66993427, 0.06549600),
         control1: topRight(1.08849323, 0.00000000),
         control2: topRight(0.86840689, 0.00000000)
      )
      path.addLine(to: topRight(0.63149399, 0.07491100))
      path.addCurve(
         to: topRight(0.07491176, 0.63149399),
         control1: topRight(0.37282392, 0.16905899),
         control2: topRight(0.16906013, 0.37282401)
      )
      path.addCurve(
         to: topRight(0.00000000, 1.52866483),
         control1: topRight(0.00000000, 0.86840701),
         control2: topRight(0.00000000, 1.08849299)
      )
      path.addLine(to: bottomRight(0.00000000, 1.52866471))
      path.addCurve(
         to: bottomRight(0.06549569, 0.66993493),
         control1: bottomRight(0.00000000, 1.08849323),
         control2: bottomRight(0.00000000, 0.86840689)
      )
      path.addLine(to: bottomRight(0.07491111, 0.63149399))
      path.addCurve(
         to: bottomRight(0.63149399, 0.07491111),
         control1: bottomRight(0.16905883, 0.37282392),
         control2: bottomRight(0.37282392, 0.16905883)
      )
      path.addCurve(
         to: bottomRight(1.52866471, 0.00000000),
         control1: bottomRight(0.86840689, 0.00000000),
         control2: bottomRight(1.08849323, 0.00000000)
      )
      path.addLine(to: bottomLeft(1.52866483, 0.00000000))
      path.addCurve(
         to: bottomLeft(0.66993397, 0.06549569),
         control1: bottomLeft(1.08849299, 0.00000000),
         control2: bottomLeft(0.86840701, 0.00000000)
      )
      path.addLine(to: bottomLeft(0.63149399, 0.07491111))
      path.addCurve(
         to: bottomLeft(0.07491100, 0.63149399),
         control1: bottomLeft(0.37282401, 0.16905883),
         control2: bottomLeft(0.16906001, 0.37282392)
      )
      path.addCurve(
         to: bottomLeft(0.00000000, 1.52866471),
         control1: bottomLeft(0.00000000, 0.86840689),
         control2: bottomLeft(0.00000000, 1.08849323)
      )
      path.addLine(to: topLeft(0.00000000, 1.52866483))
      path.addCurve(
         to: topLeft(0.06549600, 0.66993397),
         control1: topLeft(0.00000000, 1.08849299),
         control2: topLeft(0.00000000, 0.86840701)
      )
      path.addLine(to: topLeft(0.07491100, 0.63149399))
      path.addCurve(
         to: topLeft(0.63149399, 0.07491100),
         control1: topLeft(0.16906001, 0.37282401),
         control2: topLeft(0.37282401, 0.16906001)
      )
      path.addCurve(
         to: topLeft(1.52866483, 0.00000000),
         control1: topLeft(0.86840701, 0.00000000),
         control2: topLeft(1.08849299, 0.00000000)
      )

      path.closeSubpath()

      return path
   }
}