From e3eb04422eaeb5e7b777f0377448956a70537549 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 16 Feb 2023 12:41:37 +0100
Subject: [PATCH] Ease requirements on `Arc`'s start/end angles

Don't require `start < end`. The rest of the system doesn't need this,
and it makes `Arc` itself simpler.
---
 crates/fj-kernel/src/builder/edge.rs |  8 ++---
 crates/fj-math/src/arc.rs            | 48 +++++++---------------------
 2 files changed, 13 insertions(+), 43 deletions(-)

diff --git a/crates/fj-kernel/src/builder/edge.rs b/crates/fj-kernel/src/builder/edge.rs
index 6ad4a737f..87c4fb2fb 100644
--- a/crates/fj-kernel/src/builder/edge.rs
+++ b/crates/fj-kernel/src/builder/edge.rs
@@ -119,12 +119,8 @@ impl HalfEdgeBuilder for PartialHalfEdge {
             .write()
             .update_as_circle_from_center_and_radius(arc.center, arc.radius);
 
-        let [a_curve, b_curve] = if arc.flipped_construction {
-            [arc.end_angle, arc.start_angle]
-        } else {
-            [arc.start_angle, arc.end_angle]
-        }
-        .map(|coord| Point::from([coord]));
+        let [a_curve, b_curve] =
+            [arc.start_angle, arc.end_angle].map(|coord| Point::from([coord]));
 
         for (vertex, point_curve) in
             self.vertices.each_mut_ext().zip_ext([a_curve, b_curve])
diff --git a/crates/fj-math/src/arc.rs b/crates/fj-math/src/arc.rs
index 0cd991056..b7baee920 100644
--- a/crates/fj-math/src/arc.rs
+++ b/crates/fj-math/src/arc.rs
@@ -19,9 +19,6 @@ pub struct Arc {
     ///
     /// Guaranteed to be greater than `end_angle`.
     pub end_angle: Scalar,
-
-    /// True if `start` and `end` were switched to ensure `end_angle` > `start_angle`
-    pub flipped_construction: bool,
 }
 
 impl Arc {
@@ -46,17 +43,15 @@ impl Arc {
         let flipped_construction = angle_rad <= Scalar::ZERO;
         let angle_rad = angle_rad.abs();
 
-        let [p0, p1] = if flipped_construction {
-            [p1, p0]
-        } else {
-            [p0, p1]
-        };
-
-        let (uv_factor, end_angle_offset) = if angle_rad > Scalar::PI {
+        let (mut uv_factor, end_angle_offset) = if angle_rad > Scalar::PI {
             (Scalar::from_f64(-1.), Scalar::TAU)
         } else {
             (Scalar::ONE, Scalar::ZERO)
         };
+        if flipped_construction {
+            uv_factor *= -1.;
+        }
+
         let unit_vector_p0_to_p1 =
             (p1 - p0) / distance_between_endpoints * uv_factor;
         let unit_vector_midpoint_to_center =
@@ -78,7 +73,6 @@ impl Arc {
             radius,
             start_angle,
             end_angle,
-            flipped_construction,
         }
     }
 }
@@ -143,7 +137,6 @@ mod tests {
 
         dbg!(arc.start_angle);
         dbg!(arc.end_angle);
-        dbg!(arc.flipped_construction);
         assert_abs_diff_eq!(arc.center, center, epsilon = epsilon);
         assert_abs_diff_eq!(
             arc.radius,
@@ -151,30 +144,11 @@ mod tests {
             epsilon = epsilon
         );
 
-        if a0 < a1 {
-            assert!(!arc.flipped_construction);
-            assert_abs_diff_eq!(
-                arc.start_angle,
-                Scalar::from(a0),
-                epsilon = epsilon
-            );
-            assert_abs_diff_eq!(
-                arc.end_angle,
-                Scalar::from(a1),
-                epsilon = epsilon
-            );
-        } else {
-            assert!(arc.flipped_construction);
-            assert_abs_diff_eq!(
-                arc.end_angle,
-                Scalar::from(a0),
-                epsilon = epsilon
-            );
-            assert_abs_diff_eq!(
-                arc.start_angle,
-                Scalar::from(a1),
-                epsilon = epsilon
-            );
-        }
+        assert_abs_diff_eq!(
+            arc.start_angle,
+            Scalar::from(a0),
+            epsilon = epsilon
+        );
+        assert_abs_diff_eq!(arc.end_angle, Scalar::from(a1), epsilon = epsilon);
     }
 }