From 94a0cdef77cba80badc4d11f17c9596029f05194 Mon Sep 17 00:00:00 2001
From: bherbruck <brennen.herbruck@gmail.com>
Date: Thu, 8 Oct 2026 03:34:01 +0000
Subject: [PATCH] Ellipse dimensions: major radius (type major: centre to axis
 end) and minor radius (a radius dimension on the ellipse)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL
---
 crates/engine/src/cmd/sketch.rs              | 12 ++++++++++++
 crates/engine/src/cmd/sketch_modify_tests.rs | 10 ++++++++++
 crates/sketch/src/model.rs                   |  2 ++
 crates/sketch/src/solver.rs                  | 14 ++++++++++++--
 4 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/cmd/sketch.rs b/crates/engine/src/cmd/sketch.rs
index d1ac4bab..7b020715 100644
--- a/crates/engine/src/cmd/sketch.rs
+++ b/crates/engine/src/cmd/sketch.rs
@@ -1060,6 +1060,18 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
                 let len = arc_len(sk, c).ok_or_else(|| bad(cmd, "arc length needs an arc"))?;
                 (ConstraintKind::ArcLength { c, value: len }, len)
             }
+            ((None, Some(c)), None) if matches!(sk.curves.get(c).map(|x| &x.kind), Some(CurveKind::Ellipse { .. })) => {
+                // Ellipse: the major radius is the centre–axis-end distance, the minor its own.
+                let Some(CurveKind::Ellipse { c: cp, m, r }) = sk.curves.get(c).map(|x| x.kind.clone()) else {
+                    return Err(bad(cmd, "ellipse"));
+                };
+                if ty == "major" {
+                    let d = sk.point(cp).zip(sk.point(m)).map(|(a, b)| a.dist(b)).unwrap_or(0.0);
+                    (ConstraintKind::Distance { p: cp, q: m, value: d }, d)
+                } else {
+                    (ConstraintKind::Radius { c, value: r }, r)
+                }
+            }
             ((None, Some(c)), None) => {
                 let r = sk.radius(c).ok_or_else(|| bad(cmd, "cannot dimension that curve"))?;
                 let diameter = ty == "diameter" || (ty != "radius" && is_circle(c));
diff --git a/crates/engine/src/cmd/sketch_modify_tests.rs b/crates/engine/src/cmd/sketch_modify_tests.rs
index b52481ec..e0bc7a66 100644
--- a/crates/engine/src/cmd/sketch_modify_tests.rs
+++ b/crates/engine/src/cmd/sketch_modify_tests.rs
@@ -382,3 +382,13 @@ fn trim_and_break_free_form_curves_exactly() {
         assert!(d < 0.05, "{q:?} {d}");
     }
 }
+
+#[test]
+fn ellipse_radii_dimensions() {
+    let mut s = new_sketch();
+    let e = ids(&run(&mut s, "CircleElipse", json!({"center": [0, 0], "major": [10, 0], "minor_radius": 4}))["curves"])[0].clone();
+    run(&mut s, "SketchDimension", json!({"entities": [e], "type": "major", "value": 12}));
+    run(&mut s, "SketchDimension", json!({"entities": [e], "value": 5}));
+    let a = profiles(&s)[0];
+    assert!((a - std::f64::consts::PI * 60.0).abs() < 1e-6, "{a}");
+}
diff --git a/crates/sketch/src/model.rs b/crates/sketch/src/model.rs
index a96e8d5f..4aa71ea2 100644
--- a/crates/sketch/src/model.rs
+++ b/crates/sketch/src/model.rs
@@ -647,6 +647,8 @@ impl Sketch {
                 need_line(a)?;
                 need_line(b)?;
             }
+            // On an ellipse, a radius dimension holds its minor radius.
+            Radius { c, .. } if matches!(self.curves.get(c).map(|x| &x.kind), Some(CurveKind::Ellipse { .. })) => {}
             Radius { c, .. } | Diameter { c, .. } => need_round(c)?,
             Concentric { a, b } => {
                 need_round(a)?;
diff --git a/crates/sketch/src/solver.rs b/crates/sketch/src/solver.rs
index 620e0359..87890ef2 100644
--- a/crates/sketch/src/solver.rs
+++ b/crates/sketch/src/solver.rs
@@ -157,6 +157,16 @@ impl State<'_> {
             _ => Vec::new(),
         }
     }
+    /// Radius of a circle or arc; an ellipse's minor radius.
+    fn radius_of(&self, c: usize) -> f64 {
+        match self.sk.curves.get(c).map(|x| &x.kind) {
+            Some(CurveKind::Ellipse { r, .. }) => match self.lay.rvar.get(c).copied().flatten() {
+                Some(v) => self.x.get(v).copied().unwrap_or(*r),
+                None => *r,
+            },
+            _ => self.round(c).1,
+        }
+    }
     fn ends(&self, c: usize) -> Option<(usize, usize)> {
         self.sk.curves.get(c)?.kind.ends()
     }
@@ -358,7 +368,7 @@ fn residuals(s: &State, k: &ConstraintKind, out: &mut Vec<f64>) {
             let (a, b) = s.line(l);
             out.push(a.dist(b) - value);
         }
-        Radius { c, value } => out.push(s.round(c).1 - value),
+        Radius { c, value } => out.push(s.radius_of(c) - value),
         Diameter { c, value } => out.push(2.0 * s.round(c).1 - value),
         Angle { a, b, value, flip } => {
             let (a0, a1) = s.line(a);
@@ -408,7 +418,7 @@ fn measure(s: &State, k: &ConstraintKind) -> Option<f64> {
             let (a, b) = s.line(l);
             a.dist(b)
         }
-        Radius { c, .. } => s.round(c).1,
+        Radius { c, .. } => s.radius_of(c),
         Diameter { c, .. } => 2.0 * s.round(c).1,
         Angle { a, b, flip, .. } => {
             let (a0, a1) = s.line(a);