Update arc.rs with improved documentation

CHANGELOG.md

@@ -87,6 +87,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `TextInput` pasting text when `Alt` key is pressed. [#2006](https://github.com/iced-rs/iced/pull/2006)
 - Broken link to old `iced_native` crate in `README`. [#2024](https://github.com/iced-rs/iced/pull/2024)
 - `Rectangle::contains` being non-exclusive. [#2017](https://github.com/iced-rs/iced/pull/2017)
+- Documentation for `Arc` and `arc::Elliptical`. [#2008](https://github.com/iced-rs/iced/pull/2008)
 
 Many thanks to...
 
@@ -115,6 +116,7 @@ Many thanks to...
 - @rs017991
 - @tarkah
 - @thunderstorm010
+- @ua-kxie
 - @wash2
 - @wiiznokes
 

graphics/src/geometry/path/arc.rs

@@ -8,9 +8,9 @@ pub struct Arc {
  pub center: Point,
  /// The radius of the arc.
  pub radius: f32,
- /// The start of the segment's angle, clockwise rotation.
+ /// The start of the segment's angle in radians, clockwise rotation from positive x-axis.
  pub start_angle: f32,
- /// The end of the segment's angle, clockwise rotation.
+ /// The end of the segment's angle in radians, clockwise rotation from positive x-axis.
  pub end_angle: f32,
 }
 
@@ -19,13 +19,13 @@ pub struct Arc {
 pub struct Elliptical {
  /// The center of the arc.
  pub center: Point,
- /// The radii of the arc's ellipse, defining its axes.
+ /// The radii of the arc's ellipse. The horizontal and vertical half-dimensions of the ellipse will match the x and y values of the radii vector.
  pub radii: Vector,
- /// The rotation of the arc's ellipse.
+ /// The clockwise rotation of the arc's ellipse.
  pub rotation: f32,
- /// The start of the segment's angle, clockwise rotation.
+ /// The start of the segment's angle in radians, clockwise rotation from positive x-axis.
  pub start_angle: f32,
- /// The end of the segment's angle, clockwise rotation.
+ /// The end of the segment's angle in radians, clockwise rotation from positive x-axis.
  pub end_angle: f32,
 }