Add support for Swift Package Manager

Package.swift

@@ -0,0 +1,29 @@
+// swift-tools-version: 5.8
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "YMTreeMap",
+    platforms: [
+        .iOS(.v11),
+        .macOS(.v10_13),
+    ],
+    products: [
+        // Products define the executables and libraries a package produces, making them visible to other packages.
+        .library(
+            name: "YMTreeMap",
+            targets: ["YMTreeMap"]
+        )
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package, defining a module or a test suite.
+        // Targets can depend on other targets in this package and products from dependencies.
+        .target(
+            name: "YMTreeMap",
+            path: "",
+            exclude: ["Example", "Research"],
+            sources: ["YMTreeMap.swift"]
+        )
+    ]
+)

README.md

@@ -12,6 +12,7 @@ The output rectangles can easily be used to render the shapes using whatever ren
  - Using CoreGraphics (in drawRect, etc)
  - Using OpenGL
  - Using a custom UICollectionView layout
+ - Using a SwiftUI view
 
 ## Usage
 
@@ -100,13 +101,17 @@ To run the example project, clone the repo, and run `pod install` from the Examp
 
 ## Installation
 
-YMTreeMap is available through [CocoaPods](http://cocoapods.org). To install
-it, simply add the following line to your Podfile:
+YMTreeMap is available through [CocoaPods](http://cocoapods.org) and [Swift Package Manager](https://www.swift.org/package-manager/).
+To install it, simply add the following line to your Podfile or Package.swift file:
 
 ```ruby
 pod 'YMTreeMap'
 ```
 
+```swift
+.package(name: "YMTreeMap", url: "https://github.com/yahoo/YMTreeMap.git",
+```
+
 ## Further Reading
 
 Various papers on treemapping layout algorithms and usability that helped influence this project. A copy of each paper is in the Research folder.

YMTreeMap.swift

@@ -2,6 +2,7 @@
 //  Copyright 2017 Yahoo Holdings Inc.
 
 import Foundation
+import CoreGraphics
 
 @objc public class YMTreeMap: NSObject {
 
@@ -291,7 +292,7 @@ import Foundation
 
 // MARK: Platform Extensions for NSRect/CGRect
 
-public extension YMTreeMap {
+extension YMTreeMap {
 
     #if os(iOS) || os(tvOS) || os(watchOS)
     public typealias SystemRect = CGRect
@@ -305,13 +306,13 @@ public extension YMTreeMap {
     }
 }
 
-internal extension YMTreeMap.Rect {
+extension YMTreeMap.Rect {
     internal var toSystemRect: YMTreeMap.SystemRect {
         return YMTreeMap.SystemRect(x: x, y: y, width: width, height: height)
     }
 }
 
-internal extension YMTreeMap.SystemRect {
+extension YMTreeMap.SystemRect {
     internal var toYMTreeMapRect: YMTreeMap.Rect {
         return YMTreeMap.Rect(x: Double(minX),
                               y: Double(minY),