Add support for slicing from directional edges

Paralayout/GeometryAdditions.swift

@@ -91,6 +91,13 @@ extension CGSize {
 
 // MARK: -
 
+public enum DirectionalEdge {
+ case top
+ case bottom
+ case leading
+ case trailing
+}
+
 extension CGRect {
 
  /// Initialize a CGRect with bounding coordinates (always with non-negative size).
@@ -141,10 +148,35 @@ extension CGRect {
  public func offset(by offset: UIOffset) -> CGRect {
  return CGRect(origin: origin.offset(by: offset), size: size)
  }
-
+
+ /// Divides the receiver in two.
+ ///
+ /// - parameter edge: The edge from which the amount is interpreted.
+ /// - parameter amount: The size of the slice (absolute).
+ /// - returns: A tuple (slice: A rect with a width/height of the `amount`, remainder: A rect with a width/height of
+ /// the receiver reduced by `amount`).
+ public func slice(
+ from edge: DirectionalEdge,
+ amount: CGFloat,
+ in layoutDirectionProvider: LayoutDirectionProviding
+ ) -> (slice: CGRect, remainder: CGRect) {
+ switch (edge, layoutDirectionProvider.effectiveUserInterfaceLayoutDirection) {
+ case (.top, _):
+ slice(from: .minYEdge, amount: amount)
+ case (.bottom, _):
+ slice(from: .maxYEdge, amount: amount)
+ case (.leading, .leftToRight), (.trailing, .rightToLeft):
+ slice(from: .minXEdge, amount: amount)
+ case (.trailing, .leftToRight), (.leading, .rightToLeft):
+ slice(from: .maxXEdge, amount: amount)
+ @unknown default:
+ fatalError("Unknown user interface layout direction")
+ }
+ }
+
  /// Divides the receiver in two.
  ///
- /// - parameter from: The edge from which the amount is interpreted.
+ /// - parameter edge: The edge from which the amount is interpreted.
  /// - parameter amount: The size of the slice (absolute).
  /// - returns: A tuple (slice: A rect with a width/height of the `amount`, remainder: A rect with a width/height of
  /// the receiver reduced by `amount`).