Fix arc on WinUIBackend

Author: bbrk24

Examples/Sources/PathsExample/PathsApp.swift

@@ -12,13 +12,10 @@ struct ArcShape: StyledShape {
     let strokeStyle: StrokeStyle? = StrokeStyle(width: 5.0)
 
     func path(in bounds: Path.Rect) -> Path {
-        let radius = min(bounds.width, bounds.height) / 2.0 - 2.5
-
-        return Path()
-            .move(to: bounds.center + radius * SIMD2(x: cos(startAngle), y: sin(startAngle)))
+        Path()
             .addArc(
                 center: bounds.center,
-                radius: radius,
+                radius: min(bounds.width, bounds.height) / 2.0 - 2.5,
                 startAngle: startAngle,
                 endAngle: endAngle,
                 clockwise: clockwise

Sources/SwiftCrossUI/Path.swift

@@ -267,13 +267,6 @@ public struct Path {
     }
 
     /// Add an arc segment to the path.
-    ///
-    /// The behavior is not defined if the starting point is not what is implied by `center`,
-    /// `radius`, and `startAngle`. Some backends (such as UIKit) will add a line segment
-    /// to connect the arc to the starting point, while others (such as WinUI) will move the
-    /// arc in unintuitive ways. If this arc is the first segment of the current path, or
-    /// the previous segment was a rectangle or circle, be sure to call ``move(to:)`` before
-    /// this.
     /// - Parameters:
     ///   - center: The location of the center of the circle.
     ///   - radius: The radius of the circle.

Sources/WinUIBackend/WinUIBackend.swift

@@ -1293,6 +1293,10 @@ public final class WinUIBackend: AppBackend {
                     let endAngle,
                     let clockwise
                 ):
+                    let startPoint = Point(
+                        x: Float(center.x + radius * cos(startAngle)),
+                        y: Float(center.y + radius * sin(startAngle))
+                    )
                     let endPoint = Point(
                         x: Float(center.x + radius * cos(endAngle)),
                         y: Float(center.y + radius * sin(endAngle))
@@ -1301,6 +1305,16 @@ public final class WinUIBackend: AppBackend {
 
                     let figure = requirePathFigure(geometry, lastPoint: lastPoint)
 
+                    if startPoint != lastPoint {
+                        if figure.segments.size > 0 {
+                            let connector = LineSegment()
+                            connector.point = startPoint
+                            figure.segments.append(connector)
+                        } else {
+                            figure.startPoint = startPoint
+                        }
+                    }
+
                     let segment = ArcSegment()
 
                     if clockwise {