Sketch constraints and dimensions: Curvature (G2, ConstraintSmooth) and Polygon constraints; redundant constraints and dimensions are refused as over-constraining (Fusion behaviour), with driven (reference) dimensions that measure instead; arc length and linear diameter (about a centerline) dimensions; sketch.glyphs (constraint glyph anchors, conflicts) and sketch.snap (coincident/midpoint/on-curve/horizontal/vertical inference); solver damping floor keeps weakly seen variables from flying off

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/cmd/mod.rs

@@ -10,6 +10,7 @@ pub use features::auto_operation;
 mod file;
 mod inspect;
 mod sketch;
+mod sketch_constraints;
 mod sketch_create;
 mod sketch_modify;
 mod sketch_project;
@@ -110,6 +111,7 @@ pub fn command_specs() -> Vec<&'static CommandSpec> {
     let mut v: Vec<&'static CommandSpec> = Vec::new();
     v.extend(sketch::COMMANDS.iter());
     v.extend(sketch_create::COMMANDS.iter());
+    v.extend(sketch_constraints::COMMANDS.iter());
     v.extend(sketch_modify::COMMANDS.iter());
     v.extend(sketch_project::COMMANDS.iter());
     v.extend(features::COMMANDS.iter());

crates/engine/src/cmd/sketch.rs

@@ -786,13 +786,33 @@ fn draw_point(s: &mut Session, p: &Value) -> Result<Value> {
 // Constraints
 
 fn constrain(s: &mut Session, p: &Value, cmd: &str, f: impl FnOnce(&Sketch) -> Result<ConstraintKind>) -> Result<Value> {
+    let mut before = None;
     let (id, info) = edit(s, p, cmd, true, |sk, _| {
         let k = f(sk)?;
+        before = Some(dof_now(sk));
         add_c(sk, k)
     })?;
+    reject_redundant(before, &info, cmd)?;
     Ok(json!({"constraint": id, "sketch": info}))
 }
 
+/// Degrees of freedom of a sketch as it is.
+pub(super) fn dof_now(sk: &Sketch) -> usize {
+    solve(&mut sk.clone()).dof
+}
+
+/// A constraint that removes no degree of freedom over-constrains the sketch (Fusion refuses
+/// it); the caller's edit is rolled back by returning the error.
+pub(super) fn reject_redundant(before: Option<usize>, info: &Value, cmd: &str) -> Result<()> {
+    let after = info.get("dof").and_then(Value::as_u64).map(|d| d as usize);
+    if let (Some(b), Some(a)) = (before, after)
+        && a >= b
+    {
+        return Err(bad(cmd, "that would over-constrain the sketch (it is already determined by other constraints)"));
+    }
+    Ok(())
+}
+
 fn c_horizontal_vertical(s: &mut Session, p: &Value) -> Result<Value> {
     let cmd = "ConstraintHorizontalVertical";
     let mode = str_(p, "mode").map(str::to_ascii_lowercase);
@@ -962,7 +982,10 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
     };
     let value = expr(p, "value");
     let text_at = p.get("text_at").and_then(vec2);
+    let driven = bool_(p, "driven").unwrap_or(false);
+    let mut before = None;
     let ((param, kind_name, current), info) = edit(s, p, cmd, true, |sk, doc| {
+        before = Some(dof_now(sk));
         let ent = |r: &str| -> Result<(Option<usize>, Option<usize>)> {
             if let Some(c) = sk.curve_index(r) {
                 return Ok((None, Some(c)));
@@ -992,8 +1015,12 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
                     _ => (ConstraintKind::Length { l: c, value: a.dist(b) }, a.dist(b)),
                 }
             }
+            ((None, Some(c)), None) if ty == "arc_length" || ty == "arclength" => {
+                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) => {
-                let r = sk.radius(c).unwrap_or(1.0);
+                let r = sk.radius(c).ok_or_else(|| bad(cmd, "cannot dimension that curve"))?;
                 let diameter = ty == "diameter" || (ty != "radius" && is_circle(c));
                 if diameter { (ConstraintKind::Diameter { c, value: 2.0 * r }, 2.0 * r) } else { (ConstraintKind::Radius { c, value: r }, r) }
             }
@@ -1009,17 +1036,27 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
                 let (a, b) = line_pts(sk, l).unwrap_or_default();
                 let pq = sk.point(q).unwrap_or_default();
                 let d = (b - a).normalized().map(|d| d.cross(pq - a).abs()).unwrap_or(0.0);
-                (ConstraintKind::PointLineDistance { p: q, l, value: d }, d)
+                if diameter_about(sk, l, &ty) {
+                    (ConstraintKind::LinearDiameter { p: q, l, value: 2.0 * d }, 2.0 * d)
+                } else {
+                    (ConstraintKind::PointLineDistance { p: q, l, value: d }, d)
+                }
             }
             ((None, Some(a)), Some((None, Some(b)))) if is_line(a) && is_line(b) => {
                 let (a0, a1) = line_pts(sk, a).unwrap_or_default();
                 let (b0, b1) = line_pts(sk, b).unwrap_or_default();
                 let (da, db) = (a1 - a0, b1 - b0);
                 if da.cross(db).abs() < 1e-9 * da.len() * db.len() && ty != "angle" {
-                    // Parallel lines: distance between them.
+                    // Parallel lines: distance between them (a diameter about a centerline).
+                    let (a, b, b0) = if sk.curves.get(a).is_some_and(|c| c.centerline) { (a, b, b0) } else { (b, a, a0) };
                     let (bq, _) = line_ends(sk, b);
-                    let d = da.normalized().map(|d| d.cross(b0 - a0).abs()).unwrap_or(0.0);
-                    (ConstraintKind::PointLineDistance { p: bq, l: a, value: d }, d)
+                    let (a0, a1) = line_pts(sk, a).unwrap_or_default();
+                    let d = (a1 - a0).normalized().map(|d| d.cross(b0 - a0).abs()).unwrap_or(0.0);
+                    if diameter_about(sk, a, &ty) {
+                        (ConstraintKind::LinearDiameter { p: bq, l: a, value: 2.0 * d }, 2.0 * d)
+                    } else {
+                        (ConstraintKind::PointLineDistance { p: bq, l: a, value: d }, d)
+                    }
                 } else {
                     match text_at {
                         Some(t) => angle_by_sector(a, b, (a0, a1), (b0, b1), t).ok_or_else(|| bad(cmd, "cannot place that angle"))?,
@@ -1038,6 +1075,16 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
             _ => return Err(bad(cmd, "cannot dimension that combination of entities")),
         };
         let is_angle = k.is_angle();
+        if driven {
+            // A reference dimension: measures, no parameter.
+            let name = k.name();
+            let id = sk.add_constraint(k, None)?;
+            if let Some(c) = sk.constraints.iter_mut().find(|c| c.id == id) {
+                c.driven = true;
+            }
+            before = None;
+            return Ok((String::new(), name, cur));
+        }
         let (unit, default_expr) =
             if is_angle { ("deg", format!("{} deg", round6(cur.to_degrees()))) } else { ("mm", format!("{} mm", round6(cur))) };
         let e = value.clone().unwrap_or(default_expr);
@@ -1052,10 +1099,29 @@ fn dimension(s: &mut Session, p: &Value) -> Result<Value> {
         sk.add_constraint(k, Some(pname.clone()))?;
         Ok((pname, name, cur))
     })?;
+    if driven {
+        return Ok(json!({"param": Value::Null, "driven": true, "type": kind_name, "measured": current, "sketch": info}));
+    }
+    if reject_redundant(before, &info, cmd).is_err() {
+        return Err(bad(cmd, "that dimension would over-constrain the sketch; add it as a driven (reference) dimension with driven: true"));
+    }
     let v = s.doc.param(&param).map(|p| p.expr.clone()).unwrap_or_default();
     Ok(json!({"param": param, "type": kind_name, "expression": v, "measured": current, "sketch": info}))
 }
 
+/// Dimension a point (or a parallel line) to line `l` as a diameter: when `l` is a centerline
+/// (unless a plain distance was asked for) or when a diameter was asked for.
+fn diameter_about(sk: &Sketch, l: usize, ty: &str) -> bool {
+    ty == "diameter" || (ty == "auto" && sk.curves.get(l).is_some_and(|c| c.centerline))
+}
+
+fn arc_len(sk: &Sketch, c: usize) -> Option<f64> {
+    match sk.segs(c).first()? {
+        solvecraft_geom::Seg2::Arc { radius, sweep, .. } if matches!(sk.curves.get(c)?.kind, CurveKind::Arc { .. }) => Some(radius * sweep),
+        _ => None,
+    }
+}
+
 /// The angle dimension between two lines whose sector contains `t` (the text position): returns
 /// the constraint and the current value of that sector angle.
 fn angle_by_sector(a: usize, b: usize, (a0, a1): (Vec2, Vec2), (b0, b1): (Vec2, Vec2), t: Vec2) -> Option<(ConstraintKind, f64)> {

crates/engine/src/cmd/sketch_constraints.rs

@@ -0,0 +1,209 @@
+//! More sketch constraints (curvature, polygon), constraint glyph anchors and snapping
+//! inference for interactive tools.
+
+use serde_json::{Value, json};
+use solvecraft_geom::Vec2;
+use solvecraft_sketch::{ConstraintKind, CurveKind, Sketch};
+
+use super::sketch::{add_c, dof_now, edit, reject_redundant};
+use super::{CommandSpec, in_sketch};
+use crate::params::{bad, num, req_vec2, string_list, vec2};
+use crate::{EngineError, Result, Session};
+
+pub static COMMANDS: &[CommandSpec] = &[
+    CommandSpec::new("ConstraintSmooth", "Curvature", c_smooth)
+        .at("SKETCH", "CONSTRAINTS")
+        .icon("c_smooth")
+        .enabled(in_sketch)
+        .params("a, b: two curves sharing an end point (curvature continuous, G2)"),
+    CommandSpec::new("SketchPolygonConstraintCmd", "Polygon", c_polygon)
+        .at("SKETCH", "CONSTRAINTS")
+        .icon("c_polygon")
+        .enabled(in_sketch)
+        .params("lines: [line ids] of a closed chain: equal sides with every corner on one circle (a regular polygon)"),
+    CommandSpec::new("sketch.glyphs", "Constraint Glyphs", glyphs)
+        .enabled(in_sketch)
+        .noundo()
+        .params("sketch?: id|name: every constraint with where to draw its glyph (sketch coordinates)"),
+    CommandSpec::new("sketch.snap", "Snap Inference", snap)
+        .enabled(in_sketch)
+        .noundo()
+        .params("at: [x,y], from?: [x,y] (previous click), radius?: mm (snap distance, default 1): what a click there would snap to and infer"),
+];
+
+fn c_smooth(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "ConstraintSmooth";
+    let mut before = None;
+    let (id, info) = edit(s, p, cmd, true, |sk, _| {
+        let a = curve(sk, p.get("a"), cmd)?;
+        let b = curve(sk, p.get("b"), cmd)?;
+        before = Some(dof_now(sk));
+        add_c(sk, ConstraintKind::Smooth { a, b })
+    })?;
+    reject_redundant(before, &info, cmd)?;
+    Ok(json!({"constraint": id, "sketch": info}))
+}
+
+fn curve(sk: &Sketch, v: Option<&Value>, cmd: &str) -> Result<usize> {
+    let id = v.and_then(Value::as_str).ok_or_else(|| bad(cmd, "expected a curve id"))?;
+    sk.curve_index(id).ok_or_else(|| bad(cmd, format!("unknown curve `{id}`")))
+}
+
+fn c_polygon(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "SketchPolygonConstraintCmd";
+    let ids = string_list(p, "lines");
+    if ids.len() < 3 || ids.len() > 200 {
+        return Err(bad(cmd, "`lines` must list 3 to 200 lines of a closed chain"));
+    }
+    let (out, info) = edit(s, p, cmd, true, |sk, _| {
+        let ls: Vec<usize> = ids.iter().map(|i| sk.curve_index(i).ok_or_else(|| bad(cmd, format!("unknown curve `{i}`")))).collect::<Result<_>>()?;
+        let mut corners: Vec<usize> = Vec::new();
+        for l in &ls {
+            match sk.curves.get(*l).map(|c| &c.kind) {
+                Some(CurveKind::Line { a, b }) => {
+                    for q in [*a, *b] {
+                        if !corners.contains(&q) {
+                            corners.push(q);
+                        }
+                    }
+                }
+                _ => return Err(bad(cmd, "the polygon must be made of lines")),
+            }
+        }
+        if corners.len() != ls.len() {
+            return Err(bad(cmd, "the lines must form one closed chain"));
+        }
+        let pts: Vec<Vec2> = corners.iter().filter_map(|q| sk.point(*q)).collect();
+        let c = pts.iter().fold(Vec2::ZERO, |a, q| a + *q) / pts.len() as f64;
+        let r = pts.iter().map(|q| q.dist(c)).sum::<f64>() / pts.len() as f64;
+        let circ = sk.add_circle(c, r.max(1e-6), None, None)?;
+        if let Some(cu) = sk.curves.get_mut(circ) {
+            cu.construction = true;
+        }
+        let mut cons = Vec::new();
+        for w in ls.windows(2) {
+            cons.push(add_c(sk, ConstraintKind::Equal { a: w[0], b: w[1] })?);
+        }
+        for q in corners {
+            cons.push(add_c(sk, ConstraintKind::PointOnCurve { p: q, c: circ })?);
+        }
+        Ok(cons)
+    })?;
+    Ok(json!({"constraints": out, "sketch": info}))
+}
+
+/// Where a constraint's glyph goes (sketch coordinates): beside the middle of its first curve,
+/// or at its point.
+fn anchor(sk: &Sketch, k: &ConstraintKind) -> Option<Vec2> {
+    use ConstraintKind::*;
+    let mid = |c: usize| -> Option<Vec2> {
+        let poly = sk.polyline(c);
+        poly.get(poly.len() / 2).copied()
+    };
+    let pt = |p: usize| sk.point(p);
+    match *k {
+        Coincident { p, .. } | Fix { p } | Midpoint { p, .. } => pt(p),
+        PointOnCurve { p, .. } => pt(p),
+        HorizontalPoints { p, q } | VerticalPoints { p, q } | Symmetric { p, q, .. } => Some((pt(p)? + pt(q)?) * 0.5),
+        Horizontal { l } | Vertical { l } => mid(l),
+        Parallel { a, .. } | Perpendicular { a, .. } | Collinear { a, .. } | Equal { a, .. } | Concentric { a, .. } | Angle { a, .. } => mid(a),
+        Tangent { a, b } | Smooth { a, b } => {
+            // At the shared end when there is one.
+            let ends = |c: usize| sk.curves.get(c).and_then(|c| c.kind.ends());
+            match (ends(a), ends(b)) {
+                (Some((a0, a1)), Some((b0, b1))) => [a0, a1].into_iter().find(|x| *x == b0 || *x == b1).and_then(pt).or_else(|| mid(a)),
+                _ => mid(a),
+            }
+        }
+        Distance { p, q, .. } | DistanceX { p, q, .. } | DistanceY { p, q, .. } => Some((pt(p)? + pt(q)?) * 0.5),
+        PointLineDistance { p, .. } | LinearDiameter { p, .. } => pt(p),
+        Length { l, .. } => mid(l),
+        Radius { c, .. } | Diameter { c, .. } | ArcLength { c, .. } => mid(c),
+    }
+}
+
+fn glyphs(s: &mut Session, p: &Value) -> Result<Value> {
+    let id = match p.get("sketch") {
+        Some(Value::Number(n)) => n.as_u64(),
+        Some(Value::String(x)) => s.doc.find_feature(x).map(|f| f.id),
+        _ => s.active_sketch,
+    }
+    .ok_or_else(|| bad("sketch.glyphs", "no such sketch"))?;
+    let st = s.model.state();
+    let ss = st.sketch(id).ok_or_else(|| EngineError::Other("that sketch is not evaluated".into()))?;
+    let failing = &ss.report.failing;
+    let list: Vec<Value> = ss
+        .sketch
+        .constraints
+        .iter()
+        .map(|c| {
+            json!({
+                "id": c.id,
+                "name": c.kind.name(),
+                "dimension": c.kind.is_dimension(),
+                "driven": c.driven,
+                "value": c.kind.value(),
+                "param": c.param,
+                "at": anchor(&ss.sketch, &c.kind),
+                "failing": failing.contains(&c.id),
+            })
+        })
+        .collect();
+    Ok(json!({"sketch": id, "glyphs": list, "dof": ss.report.dof, "fully_constrained": ss.report.fully_constrained(), "conflicts": failing}))
+}
+
+/// Snap inference for a click at `at`: the nearest sketch point (coincident), the midpoint of a
+/// line, a point on a curve, and horizontal/vertical alignment with `from` or with other
+/// points. Results are ordered by priority; the first one is what a click would use.
+fn snap(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "sketch.snap";
+    let at = req_vec2(cmd, p, "at")?;
+    let from = p.get("from").and_then(vec2);
+    let r = num(p, "radius").filter(|r| *r > 0.0).unwrap_or(1.0);
+    let id = s.active_sketch.ok_or_else(|| bad(cmd, "no sketch is being edited"))?;
+    let st = s.model.state();
+    let ss = st.sketch(id).ok_or_else(|| EngineError::Other("the sketch is not evaluated".into()))?;
+    let sk = &ss.sketch;
+    let mut out: Vec<(f64, Value)> = Vec::new();
+    // Points (end points, centres, the origin).
+    for q in &sk.points {
+        let d = q.pos.dist(at);
+        if d <= r {
+            out.push((d * 0.5, json!({"type": "coincident", "point": q.id, "at": q.pos})));
+        }
+    }
+    for (i, c) in sk.curves.iter().enumerate() {
+        if let CurveKind::Line { a, b } = c.kind
+            && let (Some(pa), Some(pb)) = (sk.point(a), sk.point(b))
+        {
+            let m = (pa + pb) * 0.5;
+            let d = m.dist(at);
+            if d <= r {
+                out.push((d * 0.6, json!({"type": "midpoint", "curve": c.id, "at": m})));
+            }
+        }
+        if let Some(sh) = sk.shape(i) {
+            let q = sh.project(at);
+            if sh.dist(at) <= r && q.dist(at) <= r {
+                out.push((sh.dist(at) + r * 0.5, json!({"type": "on_curve", "curve": c.id, "at": q})));
+            }
+        }
+    }
+    // Alignment with the previous click.
+    if let Some(f) = from {
+        let d = at - f;
+        if d.y.abs() <= r && d.x.abs() > r {
+            out.push((d.y.abs() + r, json!({"type": "horizontal", "at": [at.x, f.y]})));
+        }
+        if d.x.abs() <= r && d.y.abs() > r {
+            out.push((d.x.abs() + r, json!({"type": "vertical", "at": [f.x, at.y]})));
+        }
+    }
+    out.sort_by(|a, b| a.0.total_cmp(&b.0));
+    let list: Vec<Value> = out.into_iter().take(8).map(|x| x.1).collect();
+    Ok(json!({"snaps": list}))
+}
+
+#[cfg(test)]
+#[path = "sketch_constraints_tests.rs"]
+mod tests;

crates/engine/src/cmd/sketch_constraints_tests.rs

@@ -0,0 +1,113 @@
+use serde_json::{Value, json};
+use solvecraft_geom::Vec2;
+
+use crate::Session;
+
+fn run(s: &mut Session, id: &str, p: Value) -> Value {
+    match s.execute(id, &p) {
+        Ok(v) => v,
+        Err(e) => panic!("{id} {p}: {e}"),
+    }
+}
+
+fn ids(v: &Value) -> Vec<String> {
+    v.as_array().map(|a| a.iter().filter_map(|x| x.as_str().map(str::to_string)).collect()).unwrap_or_default()
+}
+
+fn new_sketch() -> Session {
+    let mut s = Session::default();
+    run(&mut s, "SketchCreate", json!({"plane": "XY"}));
+    s
+}
+
+fn sketch(s: &Session) -> solvecraft_sketch::Sketch {
+    s.model.state().sketch(s.active_sketch.unwrap()).unwrap().sketch.clone()
+}
+
+#[test]
+fn redundant_constraints_and_dimensions_are_refused_driven_ones_measure() {
+    let mut s = new_sketch();
+    let l = ids(&run(&mut s, "DrawPolyline", json!({"points": [[0, 0], [10, 0]], "infer": true}))["curves"])[0].clone();
+    // Already horizontal (inferred).
+    let e = s.execute("ConstraintHorizontalVertical", &json!({"line": l})).unwrap_err().to_string();
+    assert!(e.contains("over-constrain"), "{e}");
+    run(&mut s, "ConstraintCoincident", json!({"a": format!("{l}.start"), "b": "origin"}));
+    run(&mut s, "SketchDimension", json!({"entities": [l], "value": 10}));
+    let si = run(&mut s, "sketch.inspect", json!({}));
+    assert_eq!(si["dof"], 0, "{si}");
+    // A second length on it over-constrains: refused, unless driven.
+    assert!(s.execute("SketchDimension", &json!({"entities": [format!("{l}.start"), format!("{l}.end")]})).is_err());
+    let d = run(&mut s, "SketchDimension", json!({"entities": [format!("{l}.start"), format!("{l}.end")], "driven": true}));
+    assert_eq!(d["driven"], true);
+    // The driven dimension follows the driving one.
+    let pname = si["constraints"].as_array().unwrap().iter().find_map(|c| c["param"].as_str().map(str::to_string)).unwrap();
+    run(&mut s, "ChangeParameterCommand", json!({"name": pname, "expression": "25 mm"}));
+    let g = run(&mut s, "sketch.glyphs", json!({}));
+    let driven = g["glyphs"].as_array().unwrap().iter().find(|x| x["driven"] == true).unwrap().clone();
+    assert!((driven["value"].as_f64().unwrap() - 25.0).abs() < 1e-7, "{driven}");
+    assert_eq!(g["fully_constrained"], true);
+}
+
+#[test]
+fn curvature_polygon_arc_length_linear_diameter() {
+    let mut s = new_sketch();
+    // A horizontal line ending where a control-point spline starts: G2 keeps the spline's
+    // start straight (zero curvature) and tangent.
+    let l = ids(&run(&mut s, "DrawPolyline", json!({"points": [[-10, 0], [0, 0]], "infer": true}))["curves"])[0].clone();
+    let sp = ids(&run(&mut s, "DrawCVMSpline3D", json!({"points": [format!("{l}.end"), [5, 2], [10, 6], [15, 15]]}))["curves"])[0].clone();
+    run(&mut s, "ConstraintSmooth", json!({"a": l, "b": sp}));
+    let sk = sketch(&s);
+    let pts: Vec<Vec2> = sk.curves[sk.curve_index(&sp).unwrap()].kind.point_ids().iter().map(|i| sk.point(*i).unwrap()).collect();
+    // Tangent: first leg along +x; zero curvature: the second leg too (collinear first three).
+    assert!((pts[1] - pts[0]).y.abs() < 1e-5, "{pts:?}");
+    assert!((pts[2] - pts[1]).cross(pts[1] - pts[0]).abs() < 1e-3, "{pts:?}");
+
+    // Polygon constraint on a rough quadrilateral: becomes a square-ish regular polygon.
+    let q = run(&mut s, "DrawPolyline", json!({"points": [[100, 0], [111, 1], [110, 9], [99, 10]], "closed": true}));
+    let ql = ids(&q["curves"]);
+    run(&mut s, "SketchPolygonConstraintCmd", json!({"lines": ql}));
+    let sk = sketch(&s);
+    let lens: Vec<f64> = ql.iter().map(|i| sk.polyline(sk.curve_index(i).unwrap())).map(|p| p[0].dist(p[p.len() - 1])).collect();
+    assert!(lens.iter().all(|x| (x - lens[0]).abs() < 1e-6), "{lens:?}");
+
+    // Arc length.
+    let a = ids(&run(&mut s, "ArcCenterTwoPoint", json!({"center": [0, 50], "start": [10, 50], "end": [0, 60]}))["curves"])[0].clone();
+    run(&mut s, "SketchDimension", json!({"entities": [a], "type": "arc_length", "value": 20}));
+    let sk = sketch(&s);
+    let ai = sk.curve_index(&a).unwrap();
+    let len = match sk.segs(ai)[0] {
+        solvecraft_geom::Seg2::Arc { radius, sweep, .. } => radius * sweep,
+        _ => 0.0,
+    };
+    assert!((len - 20.0).abs() < 1e-6, "{len}");
+
+    // Linear diameter about a centerline.
+    let cl = ids(&run(&mut s, "DrawPolyline", json!({"points": [[200, 0], [200, 50]]}))["curves"])[0].clone();
+    run(&mut s, "sketch.centerline", json!({"curves": [cl]}));
+    run(&mut s, "DrawPoint", json!({"point": [207, 10], "id": "rim"}));
+    let d = run(&mut s, "SketchDimension", json!({"entities": ["rim", cl], "value": 30}));
+    assert_eq!(d["type"], "LinearDiameterDimension", "{d}");
+    let sk = sketch(&s);
+    let rim = sk.point(sk.point_index("rim").unwrap()).unwrap();
+    let line = sk.polyline(sk.curve_index(&cl).unwrap());
+    let (a, b) = (line[0], line[line.len() - 1]);
+    let dist = (b - a).normalized().unwrap().cross(rim - a).abs();
+    assert!((dist - 15.0).abs() < 1e-6, "{rim:?} {dist}");
+}
+
+#[test]
+fn glyphs_and_snaps() {
+    let mut s = new_sketch();
+    let r = run(&mut s, "ShapeRectangleTwoPoint", json!({"p0": [0, 0], "p1": [20, 10]}));
+    let l = ids(&r["curves"]);
+    let g = run(&mut s, "sketch.glyphs", json!({}));
+    assert_eq!(g["glyphs"].as_array().unwrap().len(), 4);
+    assert!(g["glyphs"][0]["at"].is_array());
+    let sn = run(&mut s, "sketch.snap", json!({"at": [20.3, 0.2], "radius": 1}));
+    assert_eq!(sn["snaps"][0]["type"], "coincident", "{sn}");
+    let sn = run(&mut s, "sketch.snap", json!({"at": [10.2, 0.3], "radius": 1}));
+    assert_eq!(sn["snaps"][0]["type"], "midpoint", "{sn}");
+    assert_eq!(sn["snaps"][0]["curve"], json!(l[0]));
+    let sn = run(&mut s, "sketch.snap", json!({"at": [40, 10.4], "from": [30, 10], "radius": 1}));
+    assert!(sn["snaps"].as_array().unwrap().iter().any(|x| x["type"] == "horizontal"), "{sn}");
+}

crates/engine/src/tests.rs

@@ -282,6 +282,9 @@ fn hostile_params_never_panic() {
         "apex",
         "rho",
         "text",
+        "lines",
+        "driven",
+        "from",
     ];
     let mut internal = Vec::new();
     for spec in command_specs() {

crates/sketch/src/curves.rs

@@ -94,38 +94,73 @@ fn hermite(p0: Vec2, p1: Vec2, t0: Vec2, t1: Vec2, s: f64) -> Vec2 {
     p0 * (2.0 * s3 - 3.0 * s2 + 1.0) + t0 * (s3 - 2.0 * s2 + s) + p1 * (-2.0 * s3 + 3.0 * s2) + t1 * (s3 - s2)
 }
 
-/// Clamped uniform B-spline of `degree` over control points `p`, sampled.
-fn bspline_polyline(p: &[Vec2], degree: usize) -> Vec<Vec2> {
+/// Clamped uniform B-spline of `degree` over control points `p` at `t` in [0, 1] (de Boor).
+fn bspline_at(p: &[Vec2], degree: usize, t: f64) -> Vec2 {
     let n = p.len();
     let k = degree.min(n.saturating_sub(1)).max(1);
-    // Knots: k+1 zeros, uniform interior, k+1 ones.
     let spans = n - k;
     let mut knots = vec![0.0; k + 1];
     for i in 1..spans {
         knots.push(i as f64 / spans as f64);
     }
     knots.extend(std::iter::repeat_n(1.0, k + 1));
-    let total = SPAN_SAMPLES * spans;
-    (0..=total)
-        .map(|i| {
-            let t = i as f64 / total as f64;
-            // De Boor.
-            let mut s = k;
-            while s + 1 < n && knots.get(s + 1).is_some_and(|x| *x <= t) {
-                s += 1;
-            }
-            let mut d: Vec<Vec2> = (0..=k).map(|j| p.get(j + s - k).copied().unwrap_or_default()).collect();
-            for r in 1..=k {
-                for j in (r..=k).rev() {
-                    let i0 = j + s - k;
-                    let (lo, hi) = (knots.get(i0).copied().unwrap_or(0.0), knots.get(i0 + k + 1 - r).copied().unwrap_or(1.0));
-                    let a = if hi - lo > 1e-15 { (t - lo) / (hi - lo) } else { 0.0 };
-                    d[j] = d[j - 1] * (1.0 - a) + d[j] * a;
-                }
-            }
-            d[k]
-        })
-        .collect()
+    let mut s = k;
+    while s + 1 < n && knots.get(s + 1).is_some_and(|x| *x <= t) {
+        s += 1;
+    }
+    let mut d: Vec<Vec2> = (0..=k).map(|j| p.get(j + s - k).copied().unwrap_or_default()).collect();
+    for r in 1..=k {
+        for j in (r..=k).rev() {
+            let i0 = j + s - k;
+            let (lo, hi) = (knots.get(i0).copied().unwrap_or(0.0), knots.get(i0 + k + 1 - r).copied().unwrap_or(1.0));
+            let a = if hi - lo > 1e-15 { (t - lo) / (hi - lo) } else { 0.0 };
+            d[j] = d[j - 1] * (1.0 - a) + d[j] * a;
+        }
+    }
+    d[k]
+}
+
+/// Clamped uniform B-spline of `degree` over control points `p`, sampled.
+fn bspline_polyline(p: &[Vec2], degree: usize) -> Vec<Vec2> {
+    let n = p.len();
+    let k = degree.min(n.saturating_sub(1)).max(1);
+    let total = SPAN_SAMPLES * (n - k);
+    (0..=total).map(|i| bspline_at(p, degree, i as f64 / total as f64)).collect()
+}
+
+/// Point of a spline at global parameter `t` in [0, 1].
+pub fn spline_point(p: &[Vec2], control: bool, degree: u8, t: f64) -> Vec2 {
+    let t = t.clamp(0.0, 1.0);
+    if p.len() < 2 {
+        return p.first().copied().unwrap_or_default();
+    }
+    if control {
+        return bspline_at(p, degree.clamp(1, 7) as usize, t);
+    }
+    let spans = fit_spans(p);
+    let n = spans.len().max(1);
+    let x = t * n as f64;
+    let i = (x.floor() as usize).min(n - 1);
+    match spans.get(i) {
+        Some((p0, p1, t0, t1)) => hermite(*p0, *p1, *t0, *t1, x - i as f64),
+        None => p[0],
+    }
+}
+
+/// Curvature vector (towards the centre of curvature, magnitude 1/radius) of a parametric
+/// curve at an end (`at_end`), by one-sided second-order differences.
+pub fn end_curvature(f: &dyn Fn(f64) -> Vec2, at_end: bool) -> Vec2 {
+    let h = 1e-3;
+    let (t0, sgn) = if at_end { (1.0, -1.0) } else { (0.0, 1.0) };
+    let (f0, f1, f2, f3) = (f(t0), f(t0 + sgn * h), f(t0 + sgn * 2.0 * h), f(t0 + sgn * 3.0 * h));
+    let d1 = (f0 * -3.0 + f1 * 4.0 - f2) / (2.0 * h) * sgn;
+    let d2 = (f0 * 2.0 - f1 * 5.0 + f2 * 4.0 - f3) / (h * h);
+    let l2 = d1.len2();
+    if l2 < 1e-24 {
+        return Vec2::ZERO;
+    }
+    let t = d1 / l2.sqrt();
+    (d2 - t * t.dot(d2)) / l2
 }
 
 /// Polyline of a spline through (`control == false`) or over (`control`) the points.
@@ -161,20 +196,20 @@ pub fn spline_end_tangent(p: &[Vec2], control: bool, at_end: bool) -> Option<Vec
     if at_end { spans.last().and_then(|s| s.3.normalized()) } else { spans.first().and_then(|s| s.2.normalized()) }
 }
 
-/// Distance from `q` to a polyline.
-pub fn polyline_dist(poly: &[Vec2], q: Vec2) -> f64 {
-    let mut best = f64::INFINITY;
+/// Signed distance from `q` to a polyline (positive on the left of the nearest segment).
+pub fn polyline_signed_dist(poly: &[Vec2], q: Vec2) -> f64 {
+    let mut best = (f64::INFINITY, 1.0);
     for w in poly.windows(2) {
         let (a, b) = (w[0], w[1]);
         let d = b - a;
         let l2 = d.len2();
         let t = if l2 > 0.0 { ((q - a).dot(d) / l2).clamp(0.0, 1.0) } else { 0.0 };
-        best = best.min(q.dist(a + d * t));
+        let dist = q.dist(a + d * t);
+        if dist < best.0 {
+            best = (dist, if d.cross(q - a) >= 0.0 { 1.0 } else { -1.0 });
+        }
     }
-    if poly.len() == 1 {
-        best = poly[0].dist(q);
-    }
-    best
+    best.0 * best.1
 }
 
 #[cfg(test)]
@@ -195,6 +230,20 @@ mod tests {
         assert!((t.x - t.y).abs() < 1e-9);
     }
 
+    #[test]
+    fn end_curvature_of_a_circle_quarter() {
+        let w = std::f64::consts::FRAC_1_SQRT_2;
+        let rho = w / (1.0 + w);
+        let (a, x, b) = (Vec2::new(10.0, 0.0), Vec2::new(10.0, 10.0), Vec2::new(0.0, 10.0));
+        let k = end_curvature(&|t| conic_point(a, x, b, rho, t), false);
+        assert!(k.dist(Vec2::new(-0.1, 0.0)) < 1e-5, "{k:?}");
+        let k1 = end_curvature(&|t| conic_point(a, x, b, rho, t), true);
+        assert!(k1.dist(Vec2::new(0.0, -0.1)) < 1e-5, "{k1:?}");
+        // Fit splines have natural (straight) ends.
+        let p = [Vec2::new(0.0, 0.0), Vec2::new(10.0, 5.0), Vec2::new(20.0, 0.0)];
+        assert!(end_curvature(&|t| spline_point(&p, false, 3, t), false).len() < 1e-3);
+    }
+
     #[test]
     fn control_spline_is_clamped_and_conic_hits_its_ends() {
         let p = [Vec2::new(0.0, 0.0), Vec2::new(0.0, 10.0), Vec2::new(10.0, 10.0), Vec2::new(10.0, 0.0)];

crates/sketch/src/lib.rs

@@ -17,7 +17,7 @@ mod shape;
 mod solver;
 mod text;
 
-pub use curves::{MAX_SPLINE_POINTS, conic_point, ellipse_point, spline_end_tangent, spline_polyline};
+pub use curves::{MAX_SPLINE_POINTS, conic_point, ellipse_point, end_curvature, spline_end_tangent, spline_point, spline_polyline};
 pub use link::{Link, LinkGeom, LinkKind, LinkSource, MAX_LINK_ENTITIES};
 pub use model::{Constraint, ConstraintKind, Curve, CurveKind, SPoint, Sketch, SketchError};
 pub use profiles::{Profile, find_drawn_profiles, find_profiles, merge_regions};

crates/sketch/src/model.rs

@@ -248,6 +248,23 @@ pub enum ConstraintKind {
         #[serde(default, skip_serializing_if = "std::ops::Not::not")]
         flip: bool,
     },
+    /// Curvature continuity (G2) where curves `a` and `b` share an end point: tangent and
+    /// equal curvature.
+    Smooth {
+        a: usize,
+        b: usize,
+    },
+    /// Length along an arc.
+    ArcLength {
+        c: usize,
+        value: f64,
+    },
+    /// Twice the distance from point `p` to line `l` (a diameter about a centerline).
+    LinearDiameter {
+        p: usize,
+        l: usize,
+        value: f64,
+    },
 }
 
 impl ConstraintKind {
@@ -264,6 +281,8 @@ impl ConstraintKind {
             | Length { value, .. }
             | Radius { value, .. }
             | Diameter { value, .. }
+            | ArcLength { value, .. }
+            | LinearDiameter { value, .. }
             | Angle { value, .. } => Some(value),
             _ => None,
         }
@@ -278,6 +297,8 @@ impl ConstraintKind {
             | Length { value, .. }
             | Radius { value, .. }
             | Diameter { value, .. }
+            | ArcLength { value, .. }
+            | LinearDiameter { value, .. }
             | Angle { value, .. } => *value = v,
             _ => {}
         }
@@ -305,6 +326,9 @@ impl ConstraintKind {
             Radius { .. } => "RadialDimension",
             Diameter { .. } => "DiameterDimension",
             Angle { .. } => "AngularDimension",
+            Smooth { .. } => "Smooth",
+            ArcLength { .. } => "ArcLengthDimension",
+            LinearDiameter { .. } => "LinearDiameterDimension",
         }
     }
     fn indices(&self) -> (Vec<usize>, Vec<usize>) {
@@ -322,6 +346,9 @@ impl ConstraintKind {
             Midpoint { p, l } | PointLineDistance { p, l, .. } => (vec![p], vec![l]),
             Symmetric { p, q, l } => (vec![p, q], vec![l]),
             Fix { p } => (vec![p], vec![]),
+            Smooth { a, b } => (vec![], vec![a, b]),
+            ArcLength { c, .. } => (vec![], vec![c]),
+            LinearDiameter { p, l, .. } => (vec![p], vec![l]),
         }
     }
     fn remap(&mut self, pmap: &dyn Fn(usize) -> Option<usize>, cmap: &dyn Fn(usize) -> Option<usize>) -> bool {
@@ -369,6 +396,15 @@ impl ConstraintKind {
                 fc(l);
             }
             Fix { p } => fp(p),
+            Smooth { a, b } => {
+                fc(a);
+                fc(b);
+            }
+            ArcLength { c, .. } => fc(c),
+            LinearDiameter { p, l, .. } => {
+                fp(p);
+                fc(l);
+            }
         }
         ok && ok2
     }
@@ -382,6 +418,9 @@ pub struct Constraint {
     /// For dimensions: the model parameter that drives the value (e.g. `d1`).
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub param: Option<String>,
+    /// A driven (reference) dimension: it measures, it does not constrain.
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub driven: bool,
 }
 
 /// A 2D sketch. Point 0 is always the fixed sketch origin (id `origin`).
@@ -553,7 +592,7 @@ impl Sketch {
         }
         self.validate(&kind)?;
         let id = self.fresh("k");
-        self.constraints.push(Constraint { id: id.clone(), kind, param });
+        self.constraints.push(Constraint { id: id.clone(), kind, param, driven: false });
         Ok(id)
     }
 
@@ -577,8 +616,27 @@ impl Sketch {
         let need_line = |i: usize| if is_line(i) { Ok(()) } else { Err(SketchError::WrongKind(name(i), "needs a line".into())) };
         let need_round = |i: usize| if is_round(i) { Ok(()) } else { Err(SketchError::WrongKind(name(i), "needs a circle or arc".into())) };
         match *k {
-            Horizontal { l } | Vertical { l } | Length { l, .. } | Midpoint { l, .. } | Symmetric { l, .. } | PointLineDistance { l, .. } => {
-                need_line(l)?
+            Horizontal { l }
+            | Vertical { l }
+            | Length { l, .. }
+            | Midpoint { l, .. }
+            | Symmetric { l, .. }
+            | PointLineDistance { l, .. }
+            | LinearDiameter { l, .. } => need_line(l)?,
+            ArcLength { c, .. } => {
+                if !matches!(self.curves.get(c).map(|c| &c.kind), Some(CurveKind::Arc { .. })) {
+                    return Err(SketchError::WrongKind(name(c), "arc length needs an arc".into()));
+                }
+            }
+            Smooth { a, b } => {
+                let ends = |i: usize| self.curves.get(i).and_then(|c| c.kind.ends());
+                let shared = match (ends(a), ends(b)) {
+                    (Some((a0, a1)), Some((b0, b1))) => a0 == b0 || a0 == b1 || a1 == b0 || a1 == b1,
+                    _ => false,
+                };
+                if !shared || a == b {
+                    return Err(SketchError::Invalid("curvature continuity needs two curves sharing an end point".into()));
+                }
             }
             Parallel { a, b } | Perpendicular { a, b } | Collinear { a, b } | Angle { a, b, .. } => {
                 need_line(a)?;

crates/sketch/src/solver.rs

@@ -157,6 +157,43 @@ impl State<'_> {
             _ => Vec::new(),
         }
     }
+    fn ends(&self, c: usize) -> Option<(usize, usize)> {
+        self.sk.curves.get(c)?.kind.ends()
+    }
+    /// Length along an arc (counter-clockwise from its start).
+    fn arc_length(&self, c: usize) -> f64 {
+        match self.sk.curves.get(c).map(|c| &c.kind) {
+            Some(CurveKind::Arc { c: ci, a, b }) => {
+                let (cc, pa, pb) = (self.p(*ci), self.p(*a), self.p(*b));
+                let mut sw = (pb - cc).angle() - (pa - cc).angle();
+                while sw <= 1e-12 {
+                    sw += std::f64::consts::TAU;
+                }
+                cc.dist(pa) * sw
+            }
+            _ => 0.0,
+        }
+    }
+    /// Curvature vector of a curve at its point `p` (towards the centre of curvature).
+    fn curvature_at(&self, c: usize, p: usize) -> Vec2 {
+        let Some(kind) = self.sk.curves.get(c).map(|c| &c.kind) else { return Vec2::ZERO };
+        match kind {
+            CurveKind::Line { .. } | CurveKind::Ellipse { .. } => Vec2::ZERO,
+            CurveKind::Circle { .. } | CurveKind::Arc { .. } => {
+                let (cc, r) = self.round(c);
+                (cc - self.p(p)) / (r * r).max(1e-24)
+            }
+            CurveKind::Spline { pts, control, degree } => {
+                let q: Vec<Vec2> = pts.iter().map(|i| self.p(*i)).collect();
+                let at_end = pts.last() == Some(&p) && pts.first() != Some(&p);
+                crate::curves::end_curvature(&|t| crate::curves::spline_point(&q, *control, *degree, t), at_end)
+            }
+            CurveKind::Conic { a, b, apex, rho } => {
+                let (pa, pb, px) = (self.p(*a), self.p(*b), self.p(*apex));
+                crate::curves::end_curvature(&|t| crate::curves::conic_point(pa, px, pb, *rho, t), p == *b)
+            }
+        }
+    }
     /// Unit tangent of any curve at its point `p` (an end point for open free-form curves).
     fn tangent_at(&self, c: usize, p: usize) -> Option<Vec2> {
         match self.sk.curves.get(c).map(|c| &c.kind)? {
@@ -214,7 +251,7 @@ fn residuals(s: &State, k: &ConstraintKind, out: &mut Vec<f64>) {
         PointOnCurve { p, c } => {
             let pp = s.p(p);
             if s.is_freeform(c) {
-                out.push(crate::curves::polyline_dist(&s.poly(c), pp));
+                out.push(crate::curves::polyline_signed_dist(&s.poly(c), pp));
             } else if s.is_line(c) {
                 let (a, b) = s.line(c);
                 out.push(line_dist(pp, a, b));
@@ -253,15 +290,17 @@ fn residuals(s: &State, k: &ConstraintKind, out: &mut Vec<f64>) {
                 // Without a shared end point: the curves touch (closest approach zero).
                 let (f, o) = if s.is_freeform(a) { (a, b) } else { (b, a) };
                 let poly = s.poly(f);
+                // Signed gap at the closest approach (smooth through zero, unlike its size).
+                let closest = |v: &mut dyn Iterator<Item = f64>| v.fold(f64::INFINITY, |m: f64, x| if x.abs() < m.abs() { x } else { m });
                 let d = if s.is_line(o) {
                     let (p0, p1) = s.line(o);
-                    poly.iter().map(|q| line_dist(*q, p0, p1).abs()).fold(f64::INFINITY, f64::min)
+                    closest(&mut poly.iter().map(|q| line_dist(*q, p0, p1)))
                 } else if s.is_freeform(o) {
                     let other = s.poly(o);
-                    poly.iter().map(|q| crate::curves::polyline_dist(&other, *q)).fold(f64::INFINITY, f64::min)
+                    closest(&mut poly.iter().map(|q| crate::curves::polyline_signed_dist(&other, *q)))
                 } else {
                     let (cc, r) = s.round(o);
-                    poly.iter().map(|q| (q.dist(cc) - r).abs()).fold(f64::INFINITY, f64::min)
+                    closest(&mut poly.iter().map(|q| q.dist(cc) - r))
                 };
                 out.push(if d.is_finite() { d } else { 0.0 });
             } else if la || lb {
@@ -327,9 +366,63 @@ fn residuals(s: &State, k: &ConstraintKind, out: &mut Vec<f64>) {
             let target = if flip { value + std::f64::consts::PI } else { value };
             out.push(wrap_angle(ang - target) * scale.max(1e-6));
         }
+        Smooth { a, b } => {
+            let shared = match (s.ends(a), s.ends(b)) {
+                (Some((a0, a1)), Some((b0, b1))) => [a0, a1].into_iter().find(|x| *x == b0 || *x == b1),
+                _ => None,
+            };
+            let Some(p) = shared else {
+                out.extend([0.0, 0.0, 0.0]);
+                return;
+            };
+            match (s.tangent_at(a, p), s.tangent_at(b, p)) {
+                (Some(u), Some(v)) => out.push(u.cross(v) * 10.0),
+                _ => out.push(0.0),
+            }
+            let k = s.curvature_at(a, p) - s.curvature_at(b, p);
+            out.extend([k.x * 100.0, k.y * 100.0]);
+        }
+        ArcLength { c, value } => out.push(s.arc_length(c) - value),
+        LinearDiameter { p, l, value } => {
+            let (a, b) = s.line(l);
+            out.push(2.0 * line_dist(s.p(p), a, b).abs() - value);
+        }
     }
 }
 
+/// Measured value of a dimension (for driven dimensions).
+fn measure(s: &State, k: &ConstraintKind) -> Option<f64> {
+    use ConstraintKind::*;
+    Some(match *k {
+        Distance { p, q, .. } => s.p(p).dist(s.p(q)),
+        DistanceX { p, q, .. } => (s.p(q).x - s.p(p).x).abs(),
+        DistanceY { p, q, .. } => (s.p(q).y - s.p(p).y).abs(),
+        PointLineDistance { p, l, .. } => {
+            let (a, b) = s.line(l);
+            line_dist(s.p(p), a, b).abs()
+        }
+        Length { l, .. } => {
+            let (a, b) = s.line(l);
+            a.dist(b)
+        }
+        Radius { c, .. } => s.round(c).1,
+        Diameter { c, .. } => 2.0 * s.round(c).1,
+        Angle { a, b, flip, .. } => {
+            let (a0, a1) = s.line(a);
+            let (b0, b1) = s.line(b);
+            let (da, db) = (a1 - a0, b1 - b0);
+            let ang = da.cross(db).atan2(da.dot(db)) - if flip { std::f64::consts::PI } else { 0.0 };
+            ang.rem_euclid(std::f64::consts::TAU)
+        }
+        ArcLength { c, .. } => s.arc_length(c),
+        LinearDiameter { p, l, .. } => {
+            let (a, b) = s.line(l);
+            2.0 * line_dist(s.p(p), a, b).abs()
+        }
+        _ => return None,
+    })
+}
+
 /// One residual block: implicit arc radius equality, a user constraint, or a tangency at a known
 /// touch point (better conditioned than the distance form when an end point is on the curve).
 enum Block<'a> {
@@ -445,6 +538,15 @@ fn block_vars(sk: &Sketch, lay: &Layout, b: &Block) -> Vec<usize> {
                 curve(&mut v, l);
             }
             Fix { .. } => {}
+            Smooth { a, b } => {
+                curve(&mut v, a);
+                curve(&mut v, b);
+            }
+            ArcLength { c, .. } => curve(&mut v, c),
+            LinearDiameter { p, l, .. } => {
+                pt(&mut v, p);
+                curve(&mut v, l);
+            }
         },
         Block::TangentAt(_, k, p) => {
             pt(&mut v, *p);
@@ -553,11 +655,13 @@ fn lm(sk: &Sketch, lay: &Layout, blocks: &[(Block, Vec<usize>)], vars: &[usize],
             }
         }
         let mut improved = false;
+        // Damping floor: variables the residuals barely see must not take huge steps.
+        let floor = (0..n).map(|i| a.get(i, i)).fold(0.0_f64, f64::max) * 1e-4;
         for _ in 0..30 {
             let mut m = a.clone();
             for i in 0..n {
                 let d = a.get(i, i);
-                m.add(i, i, lambda * (d + 1e-9) + 1e-12);
+                m.add(i, i, lambda * (d.max(floor) + 1e-9) + 1e-12);
             }
             let rhs: Vec<f64> = g.iter().map(|v| -v).collect();
             let Some(step) = lin_solve(m, rhs) else {
@@ -625,6 +729,9 @@ pub fn solve(sk: &mut Sketch) -> SolveReport {
         }
     }
     for (i, c) in sk.constraints.iter().enumerate() {
+        if c.driven {
+            continue;
+        }
         let bl = match touch_point(sk, &c.kind) {
             Some(p) => Block::TangentAt(i, &c.kind, p),
             None => Block::User(i, &c.kind),
@@ -725,6 +832,17 @@ pub fn solve(sk: &mut Sketch) -> SolveReport {
         Some(v) => vdet(Some(v)) && vdet(Some(v + 1)),
         None => true,
     };
+    // Driven dimensions measure the solved geometry.
+    let fixed_lay = Layout { pvar: vec![None; sk.points.len()], rvar: vec![None; sk.curves.len()], n: 0 };
+    let measured: Vec<Option<f64>> =
+        sk.constraints.iter().map(|c| if c.driven { measure(&State { sk, lay: &fixed_lay, x: &[] }, &c.kind) } else { None }).collect();
+    for (c, m) in sk.constraints.iter_mut().zip(measured) {
+        if let Some(v) = m
+            && v.is_finite()
+        {
+            c.kind.set_value(v);
+        }
+    }
     let point_determined: Vec<bool> = (0..sk.points.len()).map(pdet).collect();
     let curve_determined =
         sk.curves.iter().enumerate().map(|(i, c)| c.kind.point_ids().into_iter().all(pdet) && vdet(lay.rvar.get(i).copied().flatten())).collect();

docs/parity.md

@@ -2,7 +2,7 @@
 
 Generated by `cargo xtask parity` from `xtask/data/fusion-catalog.tsv` (the toolbar commands of Fusion's Design workspace, ids and names only) and the live command registry (`solvecraft-cli commands`). A command counts as live when SolveCraft registers the same command id. This measures breadth, not depth; see ROADMAP.md and docs/oracle.md for depth.
 
-**SOLID + SKETCH: 91 / 291 commands live (31%).** All Design tabs: 184 / 1175 (16%). Registered commands: 119.
+**SOLID + SKETCH: 93 / 291 commands live (32%).** All Design tabs: 186 / 1175 (16%). Registered commands: 123.
 
 | Tab | Panel | Live | Total | % |
 |---|---|---:|---:|---:|
@@ -17,7 +17,7 @@ Generated by `cargo xtask parity` from `xtask/data/fusion-catalog.tsv` (the tool
 | SOLID | POSITION | 0 | 2 | 0% |
 | SKETCH | CREATE | 35 | 41 | 85% |
 | SKETCH | MODIFY | 12 | 12 | 100% |
-| SKETCH | CONSTRAINTS | 11 | 15 | 73% |
+| SKETCH | CONSTRAINTS | 13 | 15 | 87% |
 | SKETCH | CONFIGURE | 0 | 3 | 0% |
 | SKETCH | INSPECT | 1 | 25 | 4% |
 | SKETCH | INSERT | 2 | 13 | 15% |
@@ -189,6 +189,8 @@ Generated by `cargo xtask parity` from `xtask/data/fusion-catalog.tsv` (the tool
 - SKETCH › CONSTRAINTS › Concentric (`ConstraintConcentric`)
 - SKETCH › CONSTRAINTS › Collinear (`ConstraintCollinear`)
 - SKETCH › CONSTRAINTS › Symmetry (`ConstraintSymmetry`)
+- SKETCH › CONSTRAINTS › Curvature (`ConstraintSmooth`)
+- SKETCH › CONSTRAINTS › Polygon (`SketchPolygonConstraintCmd`)
 - SKETCH › INSPECT › Measure (`MeasureCommand`)
 - SKETCH › INSERT › Insert Mesh (`ParaMeshInsertAlignCommand`)
 - SKETCH › INSERT › Insert Component (`FusionImportCommandFromToolbar`)
@@ -339,8 +341,6 @@ Generated by `cargo xtask parity` from `xtask/data/fusion-catalog.tsv` (the tool
 - SKETCH › CREATE › Isoparametric Curve (`SketchIsoparametricCurve`)
 - SKETCH › CONSTRAINTS › AutoConstrain (`SketchAutoConstraintAndDimCmd`)
 - SKETCH › CONSTRAINTS › AutoConstrain from datum (`SketchAutoConstraintAndDimFromDatumCmd`)
-- SKETCH › CONSTRAINTS › Curvature (`ConstraintSmooth`)
-- SKETCH › CONSTRAINTS › Polygon (`SketchPolygonConstraintCmd`)
 - SKETCH › CONFIGURE › Configure (`FusionStartDesignConfigModeCmd`)
 - SKETCH › CONFIGURE › Display Configuration Table (`FusionShowDesignConfigPanelCmd`)
 - SKETCH › CONFIGURE › Create Configuration Rules (`FusionConfigurationRulesCmd`)