Add support for centering a view along an arc

README.md

@@ -35,7 +35,7 @@ Run `carthage update` to build the framework and drag the built `Framezilla.fram
 - [x] Edges with superview
 - [x] Width / Height
 - [x] Top / Left / Bottom / Right 
-- [x] CenterX / CenterY / Center (between views)
+- [x] CenterX / CenterY / Center between views / Center on arc
 - [x] SizeToFit / SizeThatFits / WidthToFit / HeightToFit
 - [x] Container
 - [x] Stack
@@ -181,6 +181,18 @@ view.configureFrame { maker in
 }
 ```
 
+### Center on arc
+
+![](img/centeredArc.png)
+
+If you need to do something like this, you can do:
+```swift
+view.configureFrame { maker in
+    maker.centerX(to: view1, radius: 0.5 * view1.bounds.width, angle: -.pi / 4.0)
+    maker.size(width: 30, height: 30)
+}
+```
+
 ## SizeToFit and SizeThatFits
 
 Very often you should configure labels, so there are some methods for comfortable work with them.

Sources/Maker.swift

@@ -795,6 +795,23 @@ public final class Maker {
                 .centerY(to: RelationView<VerticalRelation>(view: view, relation: .centerY))
     }
 
+    /// Creates center relation rotated around center of a specified view.
+    ///
+    /// Use this method when you want to center view by both axis relativity another view.
+    ///
+    /// - parameter view: The view on which you set center relation.
+    /// - parameter radius: Radius of the arc on which center point would be placed.
+    /// - parameter angle: Angle at which center point will be placed.
+    ///
+    /// - returns: `Maker` instance for chaining relations.
+
+    @discardableResult public func center(to view: UIView, radius: CGFloat, angle: CGFloat) -> Maker {
+        let offsetX = -radius * cos(-angle)
+        let offsetY = radius * sin(-angle)
+        return centerX(to: RelationView<HorizontalRelation>(view: view, relation: .centerX), offset: offsetX)
+                .centerY(to: RelationView<VerticalRelation>(view: view, relation: .centerY), offset: offsetY)
+    }
+
     /// Creates centerY relation.
     ///
     /// Use this method when you want to join centerY of current view with centerY of superview.

Tests/MakerCenterTests.swift

@@ -337,4 +337,26 @@ class MakerCenterTests: BaseTest {
         }
         XCTAssertEqual(testingView.frame, CGRect(x: 225, y: 225, width: 50, height: 50))
     }
+
+    func testThatCorrectlyConfiguresCenterToAnotherViewWithArc() {
+        testingView.configureFrame { maker in
+            maker.center(to: nestedView2, radius: 20.0, angle: 0.0)
+        }
+        XCTAssertEqual(testingView.frame, CGRect(x: 245, y: 225, width: 50, height: 50))
+
+        testingView.configureFrame { maker in
+            maker.center(to: nestedView2, radius: 20.0, angle: 0.5 * .pi)
+        }
+        XCTAssertEqual(testingView.frame, CGRect(x: 225, y: 245, width: 50, height: 50))
+
+        testingView.configureFrame { maker in
+            maker.center(to: nestedView2, radius: 20.0, angle: .pi)
+        }
+        XCTAssertEqual(testingView.frame, CGRect(x: 205, y: 225, width: 50, height: 50))
+
+        testingView.configureFrame { maker in
+            maker.center(to: nestedView2, radius: 20.0, angle: 1.5 * .pi)
+        }
+        XCTAssertEqual(testingView.frame, CGRect(x: 225, y: 205, width: 50, height: 50))
+    }
 }