Rect: add union operation (#533)

Add `Rect.union` and associated tests.

Author: compnerd

Sources/SwiftWin32/CG/Rect.swift

@@ -173,6 +173,19 @@ public struct Rect {
                 height: standardized.size.height)
   }
 
+  /// Returns the smallest rectangle that contains the two source rectangles.
+  public func union(_ rect: Rect) -> Rect {
+    guard !self.isNull else { return rect }
+    guard !rect.isNull else { return self }
+    let lhs: Rect = self.standardized, rhs: Rect = rect.standardized
+
+    let origin: Point = Point(x: min(lhs.minX, rhs.minX),
+                              y: min(lhs.minY, rhs.minY))
+    let size: Size = Size(width: max(lhs.maxX, rhs.maxX) - origin.x,
+                          height: max(lhs.maxY, rhs.maxY) - origin.y)
+    return Rect(origin: origin, size: size)
+  }
+
   /// Returns the intersection of two rectangles.
   public func intersection(_ rect: Rect) -> Rect {
     guard !self.isNull, !rect.isNull else { return .null }

Tests/CoreGraphicsTests/CoreGraphicsTests.swift

@@ -203,6 +203,33 @@ final class CoreGraphicsTests: XCTestCase {
     XCTAssertFalse(r4.intersects(r1))
   }
 
+  func testRectUnion() {
+    let r1: Rect = Rect(x: 0, y: 0, width: 50, height: 50)
+    let r2: Rect = Rect(x: 25, y: 25, width: 50, height: 50)
+    let r3: Rect = Rect(x: 100, y: 100, width: 50, height: 50)
+    let r4: Rect = Rect(x: 75, y: 75, width: -50, height: -50)
+
+    XCTAssertEqual(r1.union(r2), Rect(x: 0, y: 0, width: 75, height: 75))
+    XCTAssertEqual(r2.union(r1), Rect(x: 0, y: 0, width: 75, height: 75))
+
+    XCTAssertEqual(Rect.null.union(r1), Rect(x: 0, y: 0, width: 50, height: 50))
+    XCTAssertEqual(r1.union(Rect.null), Rect(x: 0, y: 0, width: 50, height: 50))
+
+    XCTAssertEqual(r1.union(r3), Rect(x: 0, y: 0, width: 150, height: 150))
+    XCTAssertEqual(r3.union(r1), Rect(x: 0, y: 0, width: 150, height: 150))
+
+    XCTAssertEqual(r1.union(r4), Rect(x: 0, y: 0, width: 75, height: 75))
+    XCTAssertEqual(r4.union(r1), Rect(x: 0, y: 0, width: 75, height: 75))
+
+    XCTAssertEqual(Rect.zero.union(Rect.zero), Rect.zero)
+
+    XCTAssertEqual(Rect.infinite.union(Rect.zero), Rect.infinite)
+    XCTAssertEqual(Rect.zero.union(Rect.infinite), Rect.infinite)
+
+    XCTAssertEqual(Rect.infinite.union(Rect.null), Rect.infinite)
+    XCTAssertEqual(Rect.null.union(Rect.infinite), Rect.infinite)
+  }
+
   func testRectNonstandardEquality() {
     let r1: Rect = Rect(x: 0, y: 0, width: 10, height: 10)
     let r2: Rect = Rect(x: 10, y: 10, width: -10, height: -10)
@@ -229,6 +256,7 @@ final class CoreGraphicsTests: XCTestCase {
     ("testRectInsetBy", testRectInsetBy),
     ("testRectIntersection", testRectIntersection),
     ("testRectIntersects", testRectIntersects),
+    ("testRectUnion", testRectUnion),
     ("testRectNonstandardEquality", testRectNonstandardEquality),
   ]
 }