Align arc creation and editing behavior

src/modules/draw/modify/lengthen.rs

@@ -213,33 +213,20 @@ fn lengthen_line(line: &LineEnt, pick_pt: Vec3, mode: &LenMode) -> Option<Entity
 }
 
 fn lengthen_arc(arc: &ArcEnt, pick_pt: Vec3, mode: &LenMode) -> Option<EntityType> {
-    let cx = arc.center.x as f32;
-    let cy = arc.center.y as f32;
-
     // Current arc span
     let span = arc_span_rad(arc.start_angle, arc.end_angle);
     let current_arc_len = arc.radius * span;
 
     let new_arc_len = apply_mode(current_arc_len, mode)?;
-    if new_arc_len < 1e-10 {
+    if new_arc_len < 1e-10 || new_arc_len >= std::f64::consts::TAU * arc.radius - 1.0e-9 {
         return None;
     }
     let new_span = new_arc_len / arc.radius;
 
     // Which end (start or end angle) is closer to pick?
-    let start_rad = arc.start_angle;
-    let end_rad = arc.end_angle;
-
-    let start_pt = Vec3::new(
-        cx + arc.radius as f32 * start_rad.cos() as f32,
-        pick_pt.y,
-        cy + arc.radius as f32 * start_rad.sin() as f32,
-    );
-    let end_pt = Vec3::new(
-        cx + arc.radius as f32 * end_rad.cos() as f32,
-        pick_pt.y,
-        cy + arc.radius as f32 * end_rad.sin() as f32,
-    );
+    let curve = crate::entities::curve::arc_curve(arc);
+    let start_pt = Vec3::from_array(curve.point_at(0.0).map(|value| value as f32));
+    let end_pt = Vec3::from_array(curve.point_at(1.0).map(|value| value as f32));
     let dist_start = (pick_pt - start_pt).length();
     let dist_end = (pick_pt - end_pt).length();