Add absoluteInsets size option

Author: wtmoose

SwiftMessages/Layout.swift

@@ -35,6 +35,7 @@ public struct Layout {
         public enum Dimension {
             case absolute(CGFloat)
             case relative(CGFloat, to: Boundary)
+            case absoluteInsets(CGFloat, to: Boundary)
         }
 
         public var width: Dimension?
@@ -81,6 +82,16 @@ extension Layout.Insets.Dimension {
     }
 }
 
+extension Layout.Size.Dimension {
+    var boundary: Layout.Boundary? {
+        switch self {
+        case .absolute(_): return nil
+        case .relative(_, let boundary): return boundary
+        case .absoluteInsets(_, let boundary): return boundary
+        }
+    }
+}
+
 extension Layout.Center.Dimension {
     var boundary: Layout.Boundary {
         switch self {

SwiftMessages/MaskingView.swift

@@ -417,10 +417,8 @@ class MaskingView: PassthroughView, LayoutInstalling {
         for dimension: Layout.Size.Dimension,
         extractor: (CGRect) -> CGFloat
     ) -> CGFloat {
-        switch dimension {
-        case .absolute(let dimension):
-            return dimension
-        case .relative(let percentage, let boundary):
+        let insetBounds: CGRect = {
+            guard let boundary = dimension.boundary else { return .zero }
             let insets: UIEdgeInsets
             switch boundary {
             case .superview: insets = .zero
@@ -432,7 +430,15 @@ class MaskingView: PassthroughView, LayoutInstalling {
                     insets = layoutMargins
                 }
             }
-            return extractor(bounds.inset(by: insets)) * percentage
+            return bounds.inset(by: insets)
+        }()
+        switch dimension {
+        case .absolute(let dimension):
+            return dimension
+        case .relative(let percentage, _):
+            return extractor(insetBounds) * percentage
+        case .absoluteInsets(let dimension, _):
+            return extractor(insetBounds) - dimension * 2
         }
     }