Ruled Surface: strips off an edge chain, exact where possible (#762) (#1151)

Ruled Surface: strips off an edge chain in normal, tangent, angle or direction mode, exact planes/cylinders/cones where possible, mitred or round corners, stitched into one surface body. SurfaceRuled is noted under format 21. Closes #762.

assets/locales/de.json

@@ -851,5 +851,10 @@
   "In place (surfaces)": "An Ort und Stelle (Flächen)",
   "None": "Keine",
   "Picked": "Ausgewählte",
-  "Restore outer boundary": "Äußere Begrenzung wiederherstellen"
+  "Restore outer boundary": "Äußere Begrenzung wiederherstellen",
+  "RULED SURFACE": "REGELFLÄCHE",
+  "Mitre": "Gehrung",
+  "Reference face": "Referenzfläche",
+  "Round": "Rund",
+  "Type": "Typ"
 }

assets/locales/en.json

@@ -1109,5 +1109,9 @@
   "In place (surfaces)": "In place (surfaces)",
   "None": "None",
   "Picked": "Picked",
-  "Restore outer boundary": "Restore outer boundary"
+  "Restore outer boundary": "Restore outer boundary",
+  "RULED SURFACE": "RULED SURFACE",
+  "Mitre": "Mitre",
+  "Reference face": "Reference face",
+  "Round": "Round"
 }

assets/locales/ja.json

@@ -1109,5 +1109,9 @@
   "In place (surfaces)": "その場で（サーフェス）",
   "None": "なし",
   "Picked": "選択したもの",
-  "Restore outer boundary": "外側の境界を復元"
+  "Restore outer boundary": "外側の境界を復元",
+  "RULED SURFACE": "ルールドサーフェス",
+  "Mitre": "留め継ぎ",
+  "Reference face": "参照面",
+  "Round": "丸め"
 }

assets/locales/ko.json

@@ -851,5 +851,10 @@
   "In place (surfaces)": "제자리에서 (서피스)",
   "None": "없음",
   "Picked": "선택한 항목",
-  "Restore outer boundary": "외부 경계 복원"
+  "Restore outer boundary": "외부 경계 복원",
+  "RULED SURFACE": "룰드 서피스",
+  "Mitre": "연귀",
+  "Reference face": "참조 면",
+  "Round": "둥글게",
+  "Type": "유형"
 }

assets/locales/zh.json

@@ -1109,5 +1109,9 @@
   "In place (surfaces)": "原位（曲面）",
   "None": "无",
   "Picked": "所选",
-  "Restore outer boundary": "恢复外边界"
+  "Restore outer boundary": "恢复外边界",
+  "RULED SURFACE": "直纹曲面",
+  "Mitre": "斜接",
+  "Reference face": "参考面",
+  "Round": "圆角"
 }

crates/doc/src/document.rs

@@ -138,6 +138,44 @@ pub enum Direction {
     Symmetric,
 }
 
+/// The direction a ruled surface leaves its edges (`surface.ruled`).
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Default, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum RuledMode {
+    /// Along the normal of the face beside each edge.
+    #[default]
+    Normal,
+    /// Continuing the face beside each edge.
+    Tangent,
+    /// At an angle from a reference direction (the face's normal unless one is given).
+    Angle,
+    /// Along a fixed direction.
+    Direction,
+}
+
+impl RuledMode {
+    fn is_normal(&self) -> bool {
+        *self == RuledMode::Normal
+    }
+}
+
+/// How a ruled surface's strips meet at sharp corners of its edge chain.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Default, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum RuledCorners {
+    /// Extended or cut back until they meet.
+    #[default]
+    Mitre,
+    /// Joined by a sector (inside corners are cut back).
+    Round,
+}
+
+impl RuledCorners {
+    fn is_mitre(&self) -> bool {
+        *self == RuledCorners::Mitre
+    }
+}
+
 /// Angular starts in older designs used the raw axis sign. New revolves measure starts
 /// along the same sketch-normal sweep direction as the kernel.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Default, Serialize, Deserialize)]
@@ -1078,6 +1116,27 @@ pub enum FeatureKind {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         tolerance: Option<String>,
     },
+    /// A strip of ruled surface `distance` wide hanging off the chain of `body`'s edges through
+    /// `edges`, as a new surface body: along `mode` (`angle` from `direction`, or from the
+    /// face's normal; along `direction`), from the face at `face` where it borders the chain;
+    /// `flip` puts it on the other side; sharp corners as `corners` says.
+    SurfaceRuled {
+        body: String,
+        edges: Vec<Vec3>,
+        distance: String,
+        #[serde(default, skip_serializing_if = "RuledMode::is_normal")]
+        mode: RuledMode,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        angle: Option<String>,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        direction: Option<Vec3>,
+        #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+        flip: bool,
+        #[serde(default, skip_serializing_if = "RuledCorners::is_mitre")]
+        corners: RuledCorners,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        face: Option<Vec3>,
+    },
     /// A planar surface body extended outward by `distance` past the edges through `edges`.
     SurfaceExtend {
         body: String,
@@ -1455,6 +1514,7 @@ impl FeatureKind {
             FeatureKind::Thicken { .. } => "ThickenFeature",
             FeatureKind::SurfaceTrim { .. } => "TrimFeature",
             FeatureKind::SurfaceExtend { .. } => "ExtendFeature",
+            FeatureKind::SurfaceRuled { .. } => "RuledSurfaceFeature",
             FeatureKind::Unstitch { .. } => "UnstitchFeature",
             FeatureKind::ReverseNormal { .. } => "ReverseNormalFeature",
             FeatureKind::SurfaceUntrim { .. } => "UntrimFeature",
@@ -1530,6 +1590,7 @@ impl FeatureKind {
             FeatureKind::Thicken { .. } => "Thicken",
             FeatureKind::SurfaceTrim { .. } => "Trim",
             FeatureKind::SurfaceExtend { .. } => "Extend",
+            FeatureKind::SurfaceRuled { .. } => "RuledSurface",
             FeatureKind::Unstitch { .. } => "Unstitch",
             FeatureKind::ReverseNormal { .. } => "ReverseNormal",
             FeatureKind::SurfaceUntrim { .. } => "Untrim",

crates/doc/src/eval.rs

@@ -3926,6 +3926,7 @@ fn eval_feature(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st:
         | FeatureKind::SurfaceSweep { .. }
         | FeatureKind::SurfaceLoft { .. }
         | FeatureKind::SurfaceOffset { .. }
+        | FeatureKind::SurfaceRuled { .. }
         | FeatureKind::SurfaceUntrim { .. } => surface::eval(doc, vals, f, st),
         FeatureKind::Emboss { .. }
         | FeatureKind::Rib { .. }

crates/doc/src/eval_surface.rs

@@ -1,8 +1,9 @@
 //! Evaluation of the surface features: Patch, Stitch, Thicken, Trim, Extend, Surface Extrude,
-//! Revolve, Sweep and Loft, Offset, Untrim, Unstitch and Reverse Normal (kernel `surfaces`,
+//! Revolve, Sweep and Loft, Offset, Ruled, Untrim, Unstitch and Reverse Normal (kernel `surfaces`,
-//! `surface_offset`, `surface_untrim`).
+//! `surface_offset`, `surface_ruled`, `surface_untrim`).
 
 use super::*;
+use crate::{RuledCorners, RuledMode};
 use solidcraft_geom::Seg2;
 
 pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st: &mut ModelState) -> Result<()> {
@@ -234,6 +235,30 @@ pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature,
             st.bodies.push(ModelBody::traced_new(name, made, f.id));
             Ok(())
         }
+        FeatureKind::SurfaceRuled { body, edges, distance, mode, angle, direction, flip, corners, face } => {
+            let d = val(vals, distance, Kind::Length)?;
+            let mode = match mode {
+                RuledMode::Normal => kernel::RuledMode::Normal,
+                RuledMode::Tangent => kernel::RuledMode::Tangent,
+                RuledMode::Angle => {
+                    let a = angle.as_ref().ok_or_else(|| DocError::Invalid("a ruled surface at an angle needs `angle`".into()))?;
+                    kernel::RuledMode::Angle { angle: val(vals, a, Kind::Angle)?, reference: *direction }
+                }
+                RuledMode::Direction => kernel::RuledMode::Direction(
+                    direction.ok_or_else(|| DocError::Invalid("a ruled surface along a direction needs `direction`".into()))?,
+                ),
+            };
+            let corners = match corners {
+                RuledCorners::Mitre => kernel::RuledCorners::Mitre,
+                RuledCorners::Round => kernel::RuledCorners::Round,
+            };
+            let mb = st.body(body).cloned().ok_or_else(|| DocError::Unknown(format!("body `{body}`")))?;
+            let r = kernel::Ruled { distance: d, mode, flip: *flip, corners, face: *face };
+            let made = Traced::step(kernel::ruled_surface(&mb.body, edges, &r)?, &[&mb.traced()]);
+            let name = new_name(st, f, 0);
+            st.bodies.push(ModelBody::traced_new(name, made, f.id));
+            Ok(())
+        }
         FeatureKind::SurfaceUntrim { face, holes, outer, in_place } => {
             let i = st.bodies.iter().position(|b| b.name == face.body).ok_or_else(|| DocError::Unknown(format!("body `{}`", face.body)))?;
             let Some(mb) = st.bodies.get(i).cloned() else { return Err(DocError::Invalid("body".into())) };

crates/doc/src/feature_geometry.rs

@@ -152,6 +152,17 @@ macro_rules! geometry_walk {
                         f(Pick(p));
                     }
                 }
+                FeatureKind::SurfaceRuled { edges, direction, face, .. } => {
+                    for e in edges {
+                        f(Pos(e));
+                    }
+                    if let Some(d) = direction {
+                        f(Dir(d));
+                    }
+                    if let Some(p) = face {
+                        f(Pick(p));
+                    }
+                }
                 FeatureKind::Unstitch { faces, .. } | FeatureKind::ReverseNormal { faces, .. } => {
                     for p in faces {
                         f(Pos(p));

crates/doc/src/feature_refs.rs

@@ -177,6 +177,7 @@ macro_rules! feature_walk {
                 FeatureKind::SurfaceUntrim { face, .. } => f(B(& $($m)? face.body)),
                 FeatureKind::SheetConvert { body, .. }
                 | FeatureKind::SurfaceExtend { body, .. }
+                | FeatureKind::SurfaceRuled { body, .. }
                 | FeatureKind::Unstitch { body, .. }
                 | FeatureKind::ReverseNormal { body, .. }
                 | FeatureKind::MeshConvert { body, .. } => f(B(body)),

crates/doc/src/feature_walk_tests/fixtures.rs

@@ -153,6 +153,11 @@ pub(super) fn fixtures() -> Vec<(&'static str, Value)> {
         ("reverse_normal", json!({"type": "reverse_normal", "body": "B"})),
         ("surface_untrim", json!({"type": "surface_untrim", "face": {"body": "B", "point": o}, "holes": [o], "outer": true})),
         ("surface_extend", json!({"type": "surface_extend", "body": "B", "edges": [o], "distance": "extend.distance"})),
+        (
+            "surface_ruled",
+            json!({"type": "surface_ruled", "body": "B", "edges": [o], "distance": "ruled.distance", "mode": "angle", "angle": "ruled.angle",
+                "direction": [0, 0, 1], "face": [1, 0, 0]}),
+        ),
         ("surface_trim", json!({"type": "surface_trim", "body": "B", "plane": plane("trim"), "keep": o})),
         ("move", json!({"type": "move", "bodies": ["B"], "translate": ["move.x", "move.y", "move.z"], "angle": "move.angle"})),
         ("import", json!({"type": "import", "file": "a.step", "step": ""})),

crates/doc/src/feature_walk_tests/golden_exprs.txt

@@ -330,6 +330,11 @@ surface_extend
   inputs:
     Distance = extend.distance (Length)
   expressions: extend.distance
+surface_ruled
+  inputs:
+    Distance = ruled.distance (Length)
+    Angle = ruled.angle (Angle)
+  expressions: ruled.distance, ruled.angle
 surface_trim
   inputs:
     Angle = trim.angle (Angle)

crates/doc/src/feature_walk_tests/golden_geometry.txt

@@ -155,6 +155,9 @@ surface_untrim
   face points: [0, 0, 0]
 surface_extend
   moves: edges[0][0], edges[0][1], edges[0][2]
+surface_ruled
+  moves: direction[0], direction[2], edges[0][0], edges[0][1], edges[0][2], face[1], face[2]
+  face points: [1, 0, 0]
 surface_trim
   moves: keep[0], keep[1], keep[2], plane.axis_dir[0], plane.axis_dir[1], plane.axis_origin[0], plane.axis_origin[1], plane.axis_origin[2], tool.point[0], tool.point[1], tool.point[2]
 move

crates/doc/src/feature_walk_tests/golden_refs.txt

@@ -172,6 +172,8 @@ surface_untrim
   remap_bodies: face.body
 surface_extend
   remap_bodies: body
+surface_ruled
+  remap_bodies: body
 surface_trim
   remap_refs: plane.base.base.name
   remap_bodies: body, tool.body

crates/doc/src/format.rs

@@ -170,6 +170,9 @@
 //!   A `SurfaceUntrim` feature (Untrim: a `face` as `body` and `point`, optional `holes`
 //!   points, `outer` and `in_place`) is also first saved in 21; 0.11.0 asks for an update
 //!   instead of meeting a feature it can't read.
+//!   A `SurfaceRuled` feature (Ruled Surface: `body`, `edges` points, `distance`, optional
+//!   `mode`, `angle`, `direction`, `flip`, `corners` and `face`) is also first saved in 21;
+//!   0.11.0 asks for an update instead of meeting a feature it can't read.
 
 use serde_json::Value;
 

crates/doc/src/params.rs

@@ -354,6 +354,12 @@ macro_rules! feature_walk {
                 FeatureKind::Thicken { thickness, .. } => f("Thickness", thickness, L, I),
                 FeatureKind::SurfaceTrim { plane, .. } => $plane(plane, f),
                 FeatureKind::SurfaceExtend { distance, .. } => f("Distance", distance, L, I),
+                FeatureKind::SurfaceRuled { distance, angle, .. } => {
+                    f("Distance", distance, L, I);
+                    if let Some(a) = angle {
+                        f("Angle", a, A, I);
+                    }
+                }
                 FeatureKind::Unstitch { .. } | FeatureKind::ReverseNormal { .. } | FeatureKind::SurfaceUntrim { .. } => {}
                 FeatureKind::SurfaceOffset { distance, tolerance, .. } => {
                     f("Distance", distance, L, I);

crates/engine/src/cmd/surface.rs

@@ -2,7 +2,7 @@
 //! solids), and the planned surface toolset (`planned!`: registered, not built yet).
 
 use serde_json::Value;
-use solidcraft_doc::{FaceAt, FeatureKind, PlaneRef, ProfileSel, expr::Kind};
+use solidcraft_doc::{FaceAt, FeatureKind, PlaneRef, ProfileSel, RuledCorners, RuledMode, expr::Kind};
 
 use super::CommandSpec;
 use super::features::{add_feature, axis_param, check_expr, extent_param, feature_sketch, operation, plane_param, profiles, sketch_id};
@@ -50,10 +50,10 @@ pub static COMMANDS: &[CommandSpec] = &[
         .at("SURFACE", "CREATE")
         .icon("surface_offset")
         .params("faces: [[x,y,z]] (points on the faces); body?; distance: expr (signed, along the faces' normals; 0 copies the faces); chain?: bool (each pick's whole smooth chain of faces); tolerance?: expr (how far a fitted face may stray, default 0.01 mm). Planes and cylinders move exactly; other faces are fitted. A new surface body (a solid where its faces close)"),
-    planned!("surface.ruled", "Ruled Surface", "762")
+    CommandSpec::new("surface.ruled", "Ruled Surface", ruled)
         .at("SURFACE", "CREATE")
         .icon("ruled")
-        .params("planned: body; edges: [[x,y,z]] (points on an edge chain); distance: expr; mode?: normal|tangent|angle|direction; angle?: expr; direction?: [x,y,z]; flip?: bool; corners?: mitre|round"),
+        .params("body; edges: [[x,y,z]] (points on a chain of its edges, open or closed); distance: expr (how far the strip reaches); mode?: normal|tangent|angle|direction (default normal: along the normal of the face beside each edge; tangent: continuing it); angle?: expr (angle mode: from `direction`, else from the face's normal, turned away from the face; 90 deg from the normal is tangent); direction?: [x,y,z] (direction mode: the rulings; angle mode: the reference, e.g. a pull direction for a draft); face?: [x,y,z] (a point on the face the directions come from; default: the face beside the most picked edges); flip?: bool (the other side); corners?: mitre|round (sharp corners of the chain; inside corners are always cut back). Lines and arcs give exact planes, cylinders and cones, other edges a fitted ruled B-spline. A new surface body"),
     planned!("surface.boundary", "Boundary Surface", "763")
         .at("SURFACE", "CREATE")
         .icon("boundary")
@@ -236,6 +236,54 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
     add_feature(s, p, kind)
 }
 
+fn ruled(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "surface.ruled";
+    let body = str_(p, "body").ok_or_else(|| bad(cmd, "`body` is required"))?.to_string();
+    if s.model.state().body(&body).is_none() {
+        return Err(bad(cmd, format!("no body `{body}`")));
+    }
+    let edges: Vec<solidcraft_geom::Vec3> = p.get("edges").and_then(Value::as_array).map(|a| a.iter().filter_map(vec3).collect()).unwrap_or_default();
+    if edges.is_empty() || edges.len() > 10_000 {
+        return Err(bad(cmd, "`edges` must list points on a chain of the body's edges"));
+    }
+    let distance = expr(p, "distance").ok_or_else(|| bad(cmd, "`distance` is required"))?;
+    check_expr(s, &distance, Kind::Length, cmd, "distance")?;
+    let mode = match str_(p, "mode").map(str::to_ascii_lowercase).as_deref() {
+        None | Some("normal") => RuledMode::Normal,
+        Some("tangent") => RuledMode::Tangent,
+        Some("angle") => RuledMode::Angle,
+        Some("direction") => RuledMode::Direction,
+        Some(o) => return Err(bad(cmd, format!("unknown mode `{o}` (normal, tangent, angle or direction)"))),
+    };
+    let angle = match mode {
+        RuledMode::Angle => {
+            let a = expr(p, "angle").ok_or_else(|| bad(cmd, "`angle` is required with mode angle"))?;
+            check_expr(s, &a, Kind::Angle, cmd, "angle")?;
+            Some(a)
+        }
+        _ => None,
+    };
+    let direction = match (mode, p.get("direction").filter(|v| !v.is_null())) {
+        (RuledMode::Angle | RuledMode::Direction, Some(v)) => {
+            let d = vec3(v).filter(|d| d.len() > 1e-12).ok_or_else(|| bad(cmd, "`direction` must be a non-zero [x, y, z]"))?;
+            Some(d)
+        }
+        (RuledMode::Direction, None) => return Err(bad(cmd, "`direction` is required with mode direction")),
+        _ => None,
+    };
+    let corners = match str_(p, "corners").map(str::to_ascii_lowercase).as_deref() {
+        None | Some("mitre") | Some("miter") => RuledCorners::Mitre,
+        Some("round") => RuledCorners::Round,
+        Some(o) => return Err(bad(cmd, format!("unknown corners `{o}` (mitre or round)"))),
+    };
+    let face = match p.get("face").filter(|v| !v.is_null()) {
+        Some(v) => Some(vec3(v).ok_or_else(|| bad(cmd, "`face` must be [x, y, z] on a face"))?),
+        None => None,
+    };
+    let kind = FeatureKind::SurfaceRuled { body, edges, distance, mode, angle, direction, flip: bool_(p, "flip").unwrap_or(false), corners, face };
+    add_feature(s, p, kind)
+}
+
 fn bodies_param(s: &Session, p: &Value, cmd: &str) -> Result<Vec<String>> {
     let bodies = string_list(p, "bodies");
     if bodies.is_empty() {
@@ -666,6 +714,59 @@ mod tests {
         assert!(s.execute("surface.offset", &json!({"distance": 1})).is_err());
     }
 
+    /// Ruled Surface round a box top (10 × 10), 2 wide: across the top, mitred, a 14 × 14 frame
+    /// less the top (96); up the top's normal, 80; at 45° with round corners, 80 + π·√2·2; along
+    /// a direction, 2 × 10 off one edge. The strips' faces are named after the edges they stand
+    /// on. Zero, a missing direction, an unknown mode and a non-finite distance are refused, the
+    /// design left as it was; undo, redo and reopening.
+    #[test]
+    fn ruled_surface_round_a_box_top() {
+        let mut s = Session::default();
+        run(&mut s, "solid.box", json!({"length": 10, "width": 10, "height": 10, "body_name": "Box"}));
+        let rim = json!([[5, 0, 10], [10, 5, 10], [5, 10, 10], [0, 5, 10]]);
+        let top = json!([5, 5, 10]);
+        run(&mut s, "surface.ruled", json!({"body": "Box", "edges": rim, "distance": "2 mm", "mode": "tangent", "face": top, "body_name": "Flange"}));
+        assert!((area(&s, "Flange") - 96.0).abs() < 1e-9, "{}", area(&s, "Flange"));
+        assert!(s.world_state().body("Flange").unwrap().body.is_surface() && s.world_state().body("Box").is_some());
+        run(&mut s, "surface.ruled", json!({"body": "Box", "edges": rim, "distance": 2, "face": top, "body_name": "Wall"}));
+        assert!((area(&s, "Wall") - 80.0).abs() < 1e-9);
+        run(
+            &mut s,
+            "surface.ruled",
+            json!({"body": "Box", "edges": rim, "distance": 2, "mode": "angle", "angle": "45 deg", "corners": "round", "face": top, "body_name": "Draft"}),
+        );
+        let want = 80.0 + std::f64::consts::PI * 2f64.sqrt() * 2.0;
+        assert!((area(&s, "Draft") - want).abs() < want * 2e-3, "{} vs {want}", area(&s, "Draft")); // (measured on meshes)
+        run(
+            &mut s,
+            "surface.ruled",
+            json!({"body": "Box", "edges": [[5, 0, 10]], "distance": 2, "mode": "direction", "direction": [0, -1, 0], "body_name": "Lip"}),
+        );
+        let bb = solidcraft_kernel::measure(&s.world_state().body("Lip").unwrap().body).unwrap().bbox;
+        assert!((area(&s, "Lip") - 20.0).abs() < 1e-9 && (bb.min.y + 2.0).abs() < 1e-9);
+        let st = s.world_state();
+        let names = solidcraft_doc::naming::face_names(st.body("Flange").unwrap());
+        assert!(names.len() == 4 && names.iter().all(|n| !n.is_empty()), "{names:?}");
+        let before = s.doc.features.len();
+        for bad in [
+            json!({"body": "Box", "edges": rim, "distance": 0}),
+            json!({"body": "Box", "edges": rim, "distance": "1e400 mm"}),
+            json!({"body": "Box", "edges": rim, "distance": 2, "mode": "direction"}),
+            json!({"body": "Box", "edges": rim, "distance": 2, "mode": "sideways"}),
+            json!({"body": "Box", "edges": rim, "distance": 2, "mode": "angle"}),
+            json!({"body": "Box", "distance": 2}),
+            json!({"body": "Nope", "edges": rim, "distance": 2}),
+        ] {
+            assert!(s.execute("surface.ruled", &bad).is_err(), "{bad}");
+        }
+        assert_eq!(s.doc.features.len(), before);
+        run(&mut s, "edit.undo", json!({}));
+        assert!(s.world_state().body("Lip").is_none());
+        run(&mut s, "edit.redo", json!({}));
+        let cold = Session::new(solidcraft_doc::Document::from_json(&s.doc.to_json()).unwrap());
+        assert!((area(&cold, "Draft") - area(&s, "Draft")).abs() < 1e-9);
+    }
+
     /// A 40 × 20 × 2 plate with three holes of radius 2 through it at x = 10, 20, 30 on y = 10.
     fn plate_with_three_holes(s: &mut Session) {
         run(s, "solid.box", json!({"length": 40, "width": 20, "height": 2, "body_name": "Plate"}));
@@ -775,7 +876,7 @@ mod tests {
     /// as it was.
     #[test]
     fn planned_commands_refuse_and_leave_the_design_alone() {
-        let planned = ["surface.ruled", "surface.boundary", "surface.blend", "surface.fillet", "inspect.continuity"];
+        let planned = ["surface.boundary", "surface.blend", "surface.fillet", "inspect.continuity"];
         let mut s = Session::default();
         run(&mut s, "solid.box", json!({"length": 10, "width": 10, "height": 10, "body_name": "B"}));
         let before = s.doc.features.len();

crates/kernel/src/lib.rs

@@ -94,6 +94,7 @@ mod step_in;
 mod step_out;
 mod surface_kind;
 mod surface_offset;
+mod surface_ruled;
 mod surface_untrim;
 mod surfaces;
 mod sweep_path;
@@ -138,6 +139,7 @@ pub use step_in::{ImportedBody, StepImport, StepNode, step_cache_alive, step_imp
 pub use step_out::{ExportBody, ExportProduct, StepHeader, step_export_bodies, step_export_products};
 pub use surface_kind::{FaceSurface, face_surface};
 pub use surface_offset::offset_surface;
+pub use surface_ruled::{Ruled, RuledCorners, RuledMode, ruled_surface};
 pub use surface_untrim::{UntrimHoles, untrim};
 pub use surfaces::{
     copy_faces, extend, extrude_sheet, loft_sheet, patch_edges, patch_region, remove_faces, reverse_faces, revolve_sheet, stitch, sweep_sheet,

crates/kernel/src/surface_ruled.rs

@@ -0,0 +1,880 @@
+//! Ruled surfaces (Surface › Ruled): a strip hanging off a chain of a body's edges, a given
+//! width out from them, as a new surface body. Each edge carries one strip, ruled by straight
+//! lines from the edge in a direction set by the face beside it: along its normal, continuing
+//! it, at an angle from a reference direction (a draft), or along a fixed vector.
+//!
+//! A strip is exact where the rulings move the edge by an affine map: a straight edge with a
+//! constant ruling direction gives a plane, an arc whose rulings keep their angle to its axis
+//! gives a plane (a ring), a cylinder or a cone. Any other strip is a ruled B-spline (degree 1
+//! across) fitted within [`FIT_TOLERANCE`]. Strips share their side edges where their rulings
+//! agree; at a sharp corner of the chain they are mitred (each extended along its far edge
+//! until the two meet, or cut back where they overlap) or rounded (a planar or conical sector
+//! turning one ruling into the other; an inside corner is always cut back). The strips stand
+//! on the body's own edges, so they come out stitched together.
+
+use std::collections::HashMap;
+
+use mt::{BoundedCurve, ParametricCurve, ParametricSurface3D, SearchNearestParameter};
+use solidcraft_geom::Vec3;
+use truck_modeling as mt;
+
+use crate::body::{Body, from_p3, p3, v3};
+use crate::record::{Rebuild, rebuilt_body};
+use crate::surfaces::{map_control_points, nearest_face, picked_chain, surface_body};
+use crate::{KernelError, Result, guard};
+
+/// How far a fitted strip may stray from the true ruled surface (mm).
+const FIT_TOLERANCE: f64 = 1e-3;
+/// Samples along an edge when classifying its strip, and the most a fitted strip is refined to.
+const SAMPLES: usize = 16;
+const MAX_FIT_SAMPLES: usize = 513;
+/// Rulings closer than this (as unit vectors) agree: their strips share a side edge.
+const SAME_RULING: f64 = 1e-7;
+
+/// The direction a ruled strip leaves its edge.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum RuledMode {
+    /// Along the normal of the face beside the edge.
+    Normal,
+    /// Continuing the face beside the edge, square to the edge.
+    Tangent,
+    /// `angle` (radians) from `reference` (default: the face's normal), turned away from the
+    /// face about the edge: 0 is the reference, 90° square to it.
+    Angle { angle: f64, reference: Option<Vec3> },
+    /// Along a fixed vector.
+    Direction(Vec3),
+}
+
+/// How strips meet at a sharp corner of the chain.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub enum RuledCorners {
+    /// Extended (or cut back) until they meet.
+    #[default]
+    Mitre,
+    /// Joined by a sector turning one ruling into the other (inside corners are cut back).
+    Round,
+}
+
+/// A ruled surface's settings.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Ruled {
+    /// How far the strip reaches along its rulings (mm, positive).
+    pub distance: f64,
+    pub mode: RuledMode,
+    /// The strip on the other side: every ruling reversed.
+    pub flip: bool,
+    pub corners: RuledCorners,
+    /// A point on the face the directions are taken from, for the edges it borders; elsewhere
+    /// the face beside the most picked edges (the first in face order on a tie).
+    pub face: Option<Vec3>,
+}
+
+/// A ruled surface hanging off the chain of `body`'s edges picked by the points `at` (open or
+/// closed), as one surface body. The history is over `[body]`: each strip is made in place of
+/// the edge it stands on, a corner face in place of the two edges meeting there.
+pub fn ruled_surface(body: &Body, at: &[Vec3], r: &Ruled) -> Result<Body> {
+    body.require_brep("ruled surface")?;
+    let d = r.distance;
+    if !(d.is_finite() && d > 0.0 && d < 1e6) {
+        return Err(KernelError::Invalid("the ruled surface distance must be positive and finite".into()));
+    }
+    if at.is_empty() || at.len() > 10_000 {
+        return Err(KernelError::Invalid("pick the edges of a chain".into()));
+    }
+    let unit =
+        |v: Vec3, what: &str| v.normalized().filter(|u| u.is_finite()).ok_or_else(|| KernelError::Invalid(format!("the {what} has no length")));
+    let mode = match r.mode {
+        RuledMode::Angle { angle, reference } => {
+            if !(angle.is_finite() && angle.abs() <= std::f64::consts::TAU) {
+                return Err(KernelError::Invalid("the ruled surface angle must be finite, a full turn at most".into()));
+            }
+            RuledMode::Angle { angle, reference: reference.map(|v| unit(v, "reference direction")).transpose()? }
+        }
+        RuledMode::Direction(v) => RuledMode::Direction(unit(v, "direction")?),
+        m => m,
+    };
+    let picked_face = r.face.map(|p| nearest_face(body, p)).transpose()?;
+    let eps = 1e-9 * (1.0 + body.size() + d);
+    guard("ruled surface", || {
+        let (chain, closed) = picked_chain(body, at)?;
+        let faces: Vec<&mt::Face> = body.solid.face_iter().collect();
+        // The faces beside each chain edge (face index, the face's own use of the edge).
+        let mut beside: HashMap<mt::EdgeID, Vec<(usize, mt::Edge)>> = chain.iter().map(|e| (e.id(), Vec::new())).collect();
+        for (i, f) in faces.iter().enumerate() {
+            for e in f.boundaries().iter().flat_map(|w| w.edge_iter()) {
+                if let Some(list) = beside.get_mut(&e.id()) {
+                    list.push((i, e.clone()));
+                }
+            }
+        }
+        let mut count: HashMap<usize, usize> = HashMap::new();
+        for list in beside.values() {
+            for (i, _) in list {
+                *count.entry(*i).or_default() += 1;
+            }
+        }
+        let empty = Vec::new();
+        let around = |e: &mt::Edge| beside.get(&e.id()).unwrap_or(&empty);
+        // The face each edge takes its directions from: the picked face where it borders the
+        // edge, carried on along the chain to the faces meeting it smoothly (a cylinder's
+        // halves); with no picked face beside the chain, the face beside the most edges.
+        let n = chain.len();
+        let mut chosen: Vec<Option<usize>> = chain.iter().map(|e| around(e).iter().position(|(i, _)| Some(*i) == picked_face)).collect();
+        if chosen.iter().all(Option::is_none) {
+            chosen = chain
+                .iter()
+                .map(|e| {
+                    let list = around(e);
+                    (0..list.len()).max_by(|a, b| {
+                        let key = |k: &usize| list.get(*k).map(|(i, _)| (count.get(i).copied().unwrap_or(0), std::cmp::Reverse(*i)));
+                        key(a).cmp(&key(b))
+                    })
+                })
+                .collect();
+        }
+        // Carried on from a chosen neighbour across the vertex they share.
+        let normal = |face: usize, p: mt::Point3| faces.get(face).and_then(|f| normal_at(f, from_p3(p)));
+        for _ in 0..n {
+            let mut changed = false;
+            for j in 0..n {
+                if chosen.get(j).copied().flatten().is_some() {
+                    continue;
+                }
+                let Some(e) = chain.get(j) else { continue };
+                let neighbours = [
+                    (j.checked_sub(1).or(closed.then(|| n - 1)), e.front().point()),
+                    ((j + 1 < n).then_some(j + 1).or(closed.then_some(0)), e.back().point()),
+                ];
+                let pick = neighbours.iter().find_map(|(k, p)| {
+                    let k = (*k)?;
+                    let (face, _) = around(chain.get(k)?).get(chosen.get(k).copied().flatten()?)?;
+                    let want = normal(*face, *p)?;
+                    let list = around(e);
+                    (0..list.len()).max_by(|a, b| {
+                        let dot = |k: &usize| list.get(*k).and_then(|(i, _)| normal(*i, *p)).map_or(f64::NEG_INFINITY, |nn| nn.dot(want));
+                        dot(a).total_cmp(&dot(b))
+                    })
+                });
+                if let (Some(k), Some(slot)) = (pick, chosen.get_mut(j)) {
+                    *slot = Some(k);
+                    changed = true;
+                }
+            }
+            if !changed {
+                break;
+            }
+        }
+        let field = Field { mode, flip: r.flip, distance: d };
+        let mut strips = Vec::with_capacity(n);
+        for (e, k) in chain.iter().zip(&chosen) {
+            let (i, own) = k.and_then(|k| around(e).get(k)).ok_or_else(|| KernelError::Invalid("a picked edge has no face beside it".into()))?;
+            let face = faces.get(*i).ok_or_else(|| KernelError::Failed("ruled surface: a face".into()))?;
+            // The face lies left of its own boundary (seen along its normal); the strip's
+            // tangent direction points away from it.
+            let face_left = own.orientation() == e.orientation();
+            strips.push(Strip::new(e.clone(), face, face_left, &field, eps)?);
+        }
+        // Joints at the chain's vertices: joint j is where strip j starts (and strip j - 1
+        // ends); an open chain has one more, at its far end.
+        let joints = (0..n + usize::from(!closed))
+            .map(|j| {
+                let incoming = if j > 0 {
+                    strips.get(j - 1)
+                } else if closed {
+                    strips.last()
+                } else {
+                    None
+                };
+                let outgoing = strips.get(j).filter(|_| closed || j < n);
+                Joint::new(incoming, outgoing, &mode, r.corners, eps)
+            })
+            .collect::<Result<Vec<_>>>()?;
+        let mut rec = Rebuild::default();
+        let mut out = Vec::new();
+        for (j, s) in strips.iter().enumerate() {
+            let start = joints.get(j).ok_or_else(|| KernelError::Failed("ruled surface: a joint".into()))?;
+            let end = joints.get(if closed { (j + 1) % n } else { j + 1 }).ok_or_else(|| KernelError::Failed("ruled surface: a joint".into()))?;
+            let (up_start, top_start) = start.side(Side::Out, s);
+            let (up_end, top_end) = end.side(Side::In, s);
+            let top = if s.line {
+                mt::Edge::new_unchecked(&top_start, &top_end, mt::Curve::Line(mt::Line(top_start.point(), top_end.point())))
+            } else {
+                mt::Edge::new_unchecked(&top_start, &top_end, s.top.clone())
+            };
+            if s.line && (from_p3(top_end.point()) - from_p3(top_start.point())).dot(s.start.tangent) <= eps {
+                return Err(KernelError::Invalid("the corners cut a strip away entirely: try a shorter distance".into()));
+            }
+            let mut wire = vec![s.base.clone()];
+            wire.extend(up_end.iter().cloned());
+            wire.push(top.inverse());
+            wire.extend(up_start.iter().rev().map(mt::Edge::inverse));
+            let face = mt::Face::new_unchecked(vec![wire.into()], s.surface.clone());
+            rec.blend(&face, [s.base.id()]);
+            out.push(face);
+            out.extend(end.corner_faces().into_iter().cloned());
+        }
+        // Corner faces are made in place of the two edges meeting at the corner.
+        for (j, jt) in joints.iter().enumerate() {
+            let near: Vec<mt::EdgeID> = [
+                if j > 0 {
+                    strips.get(j - 1)
+                } else if closed {
+                    strips.last()
+                } else {
+                    None
+                },
+                strips.get(j),
+            ]
+            .into_iter()
+            .flatten()
+            .map(|s| s.base.id())
+            .collect();
+            for f in jt.corner_faces() {
+                rec.blend(f, near.iter().copied());
+            }
+        }
+        Ok(rebuilt_body(surface_body(out), &[&body.solid], &rec))
+    })
+}
+
+/// How the rulings are set at a point of an edge.
+struct Field {
+    mode: RuledMode,
+    flip: bool,
+    distance: f64,
+}
+
+impl Field {
+    /// The unit ruling at a point where the edge runs along `t` (unit, chain direction), the
+    /// face's normal is `n` and `out` (unit) points away from the face, square to the edge.
+    fn ruling(&self, t: Vec3, n: Vec3, out: Vec3) -> Result<Vec3> {
+        let dir = match self.mode {
+            RuledMode::Normal => n,
+            RuledMode::Tangent => out,
+            RuledMode::Angle { angle, reference } => {
+                let r = reference.unwrap_or(n);
+                let r = (r - t * r.dot(t)).normalized().ok_or_else(|| KernelError::Invalid("the reference direction runs along an edge".into()))?;
+                // Square to the reference and the edge, turned away from the face.
+                let mut w = t.cross(r);
+                if w.dot(out + n) < 0.0 {
+                    w = -w;
+                }
+                r * angle.cos() + w * angle.sin()
+            }
+            RuledMode::Direction(v) => v,
+        };
+        let dir = if self.flip { -dir } else { dir };
+        if dir.cross(t).len() < 1e-6 {
+            return Err(KernelError::Invalid("the strip would run along an edge: pick another direction".into()));
+        }
+        Ok(dir)
+    }
+}
+
+/// One end of a strip, in the chain's direction.
+#[derive(Clone, Copy)]
+struct End {
+    /// The edge's end point, the unit ruling there and where the ruling ends.
+    at: Vec3,
+    ruling: Vec3,
+    top: Vec3,
+    /// The unit tangent of the strip's far edge there, and the face's normal.
+    tangent: Vec3,
+    normal: Vec3,
+}
+
+/// The strip on one edge.
+struct Strip {
+    /// The body's edge, turned to run along the chain.
+    base: mt::Edge,
+    surface: mt::Surface,
+    /// The far edge's curve (from the start's ruling end to the end's).
+    top: mt::Curve,
+    /// A plane through a straight edge: its far edge is the line between its corners.
+    line: bool,
+    /// The strip lies in a plane.
+    planar: bool,
+    start: End,
+    end: End,
+}
+
+impl Strip {
+    fn new(base: mt::Edge, face: &mt::Face, face_left: bool, field: &Field, eps: f64) -> Result<Strip> {
+        let c = base.oriented_curve();
+        let (t0, t1) = c.range_tuple();
+        let d = field.distance;
+        // The point, unit tangent, face normal and ruling at a parameter of the edge.
+        let at = |t: f64| -> Result<(Vec3, Vec3, Vec3, Vec3)> {
+            let p = from_p3(c.subs(t));
+            let tan = from_p3(mt::Point3::new(0.0, 0.0, 0.0) + c.der(t))
+                .normalized()
+                .ok_or_else(|| KernelError::Invalid("a picked edge has a point with no direction".into()))?;
+            let n = normal_at(face, p)
+                .ok_or_else(|| KernelError::Invalid("the face beside an edge has a point with no normal there: not supported yet".into()))?;
+            let out = if face_left { tan.cross(n) } else { n.cross(tan) };
+            let out = out.normalized().ok_or_else(|| KernelError::Invalid("the face beside an edge runs along it".into()))?;
+            Ok((p, tan, n, field.ruling(tan, n, out)?))
+        };
+        let param = |k: usize, m: usize| t0 + (t1 - t0) * k as f64 / (m - 1) as f64;
+        let samples: Vec<(Vec3, Vec3, Vec3, Vec3)> = (0..SAMPLES).map(|k| at(param(k, SAMPLES))).collect::<Result<_>>()?;
+        let (Some(first), Some(last)) = (samples.first().copied(), samples.last().copied()) else {
+            return Err(KernelError::Failed("ruled surface: samples".into()));
+        };
+        let tops: Vec<Vec3> = samples.iter().map(|(p, _, _, r)| *p + *r * d).collect();
+        // A plane through the edge and its rulings, when everything lies in one.
+        let plane_normal = first.1.cross(first.3).normalized();
+        let planar =
+            plane_normal.is_some_and(|nn| samples.iter().map(|s| s.0).chain(tops.iter().copied()).all(|q| (q - first.0).dot(nn).abs() <= eps));
+        let exact = affine(&samples, d, eps).and_then(|m| map_control_points(&c, |p| m.apply(p)));
+        let line = planar && matches!(c, mt::Curve::Line(_)) && exact.is_some();
+        let (surface, top) = match (planar, exact) {
+            (true, Some(top)) => (plane(first.0, first.1, first.3), top),
+            (false, Some(top)) => {
+                let s = mt::BSplineSurface::homotopy(c.clone().lift_up(), top.clone().lift_up());
+                (mt::Surface::NurbsSurface(mt::NurbsSurface::new(s)), top)
+            }
+            (planar, None) => {
+                let (s, top) = fitted(&at, &param, d)?;
+                (if planar { plane(first.0, first.1, first.3) } else { s }, top)
+            }
+        };
+        let (s0, s1) = top.range_tuple();
+        let tangent = |s: f64| from_p3(mt::Point3::new(0.0, 0.0, 0.0) + top.der(s)).normalized().unwrap_or(first.1);
+        let end = |(p, _, n, r): (Vec3, Vec3, Vec3, Vec3), tan: Vec3| End { at: p, ruling: r, top: p + r * d, tangent: tan, normal: n };
+        Ok(Strip { start: end(first, tangent(s0)), end: end(last, tangent(s1)), base, surface, top, line, planar })
+    }
+}
+
+/// The unit normal of `face` (as it faces) at its point nearest `p`.
+fn normal_at(face: &mt::Face, p: Vec3) -> Option<Vec3> {
+    let surface = face.oriented_surface();
+    let (u, v) = surface.search_nearest_parameter(p3(p), None, 100)?;
+    from_p3(mt::Point3::new(0.0, 0.0, 0.0) + surface.normal(u, v)).normalized()
+}
+
+/// The plane through `o` spanned by the edge direction `t` and the ruling `r`, its normal t × r
+/// (the strip's own orientation).
+fn plane(o: Vec3, t: Vec3, r: Vec3) -> mt::Surface {
+    mt::Surface::Plane(mt::Plane::new(p3(o), p3(o + t), p3(o + r)))
+}
+
+/// An affine map taking each point of an edge to the end of its ruling.
+enum Affine {
+    Translate(Vec3),
+    /// Points scaled by `scale` about the axis through `c` along `a` (in its square plane),
+    /// then moved by `shift`.
+    Radial {
+        c: Vec3,
+        a: Vec3,
+        scale: f64,
+        shift: Vec3,
+    },
+}
+
+impl Affine {
+    fn apply(&self, p: Vec3) -> Vec3 {
+        match *self {
+            Affine::Translate(v) => p + v,
+            Affine::Radial { c, a, scale, shift } => {
+                let q = p - c;
+                let along = q.dot(a);
+                c + (q - a * along) * scale + a * along + shift
+            }
+        }
+    }
+}
+
+/// The affine map the rulings (scaled by `d`) make of the sampled edge, when there is one: a
+/// constant ruling translates; on a circular arc, rulings keeping their radial and axial parts
+/// (and none along the arc) scale about its axis and shift along it.
+fn affine(samples: &[(Vec3, Vec3, Vec3, Vec3)], d: f64, eps: f64) -> Option<Affine> {
+    let first = samples.first()?;
+    if samples.iter().all(|s| (s.3 - first.3).len() * d <= eps) {
+        return Some(Affine::Translate(first.3 * d));
+    }
+    let k = samples.len();
+    let (a, b, c) = (samples.get(k / 6)?.0, samples.get(k / 2)?.0, samples.get(k - 1 - k / 6)?.0);
+    let (u, v) = (b - a, c - a);
+    let w = u.cross(v);
+    let ww = w.dot(w);
+    if !(ww > 1e-24) {
+        return None;
+    }
+    let centre = a + (v.cross(w) * u.dot(u) + w.cross(u) * v.dot(v)) / (2.0 * ww);
+    let axis = w.normalized()?;
+    let radius = (a - centre).len();
+    let (mut radial, mut along) = (None, None);
+    for (p, t, _, r) in samples {
+        let q = *p - centre;
+        if q.dot(axis).abs() > eps || (q.len() - radius).abs() > eps {
+            return None;
+        }
+        let rho = q.normalized()?;
+        let (x, y) = (r.dot(rho) * d, r.dot(axis) * d);
+        if (r.dot(*t) * d).abs() > eps || radial.is_some_and(|x0: f64| (x - x0).abs() > eps) || along.is_some_and(|y0: f64| (y - y0).abs() > eps) {
+            return None;
+        }
+        radial.get_or_insert(x);
+        along.get_or_insert(y);
+    }
+    Some(Affine::Radial { c: centre, a: axis, scale: 1.0 + radial? / radius, shift: axis * along? })
+}
+
+/// A ruled B-spline fitted to the strip (degree 1 across: cubics through matching samples of
+/// the edge and of its rulings' ends), refined until both are within [`FIT_TOLERANCE`]; and its
+/// far edge.
+fn fitted(at: &dyn Fn(f64) -> Result<(Vec3, Vec3, Vec3, Vec3)>, param: &dyn Fn(usize, usize) -> f64, d: f64) -> Result<(mt::Surface, mt::Curve)> {
+    let mut m = SAMPLES + 1;
+    loop {
+        let pts: Vec<(Vec3, Vec3, Vec3, Vec3)> = (0..m).map(|k| at(param(k, m))).collect::<Result<_>>()?;
+        let near: Vec<Vec3> = pts.iter().map(|s| s.0).collect();
+        let far: Vec<Vec3> = pts.iter().map(|s| s.0 + s.3 * d).collect();
+        let fail = || KernelError::Failed("ruled surface: fitting a strip".into());
+        let (base, top) = (crate::build::interpolate_cubic(&near).ok_or_else(fail)?, crate::build::interpolate_cubic(&far).ok_or_else(fail)?);
+        // Checked between the samples, where a fit strays most.
+        let mut worst = 0.0f64;
+        for k in 0..m - 1 {
+            let s = (k as f64 + 0.5) / (m - 1) as f64;
+            let (p, _, _, r) = at(param(2 * k + 1, 2 * m - 1))?;
+            worst = worst.max(from_p3(base.subs(s)).dist(p)).max(from_p3(top.subs(s)).dist(p + r * d));
+        }
+        if worst <= FIT_TOLERANCE {
+            let surface = mt::Surface::BSplineSurface(mt::BSplineSurface::homotopy(base, top.clone()));
+            return Ok((surface, mt::Curve::BSplineCurve(top)));
+        }
+        if m >= MAX_FIT_SAMPLES {
+            return Err(KernelError::Invalid(format!("the strip can't be fitted within {FIT_TOLERANCE} mm (off by up to {worst:.4} mm)")));
+        }
+        m = (2 * m - 1).min(MAX_FIT_SAMPLES);
+    }
+}
+
+/// Which strip of a joint: the one ending there or the one starting there.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Side {
+    In,
+    Out,
+}
+
+/// How the strips meet at a vertex of the chain (or end at a free end of it).
+enum Joint {
+    /// One side edge from the vertex up the ruling: the strips' rulings agree, or a free end.
+    Shared(mt::Edge),
+    /// Mitred: the edge from the vertex to where the strips' far edges meet (`m`); a curved
+    /// strip keeps its own side edge and gets a triangle (`incoming`, `outgoing`) up to it.
+    Mitre { edge: mt::Edge, m: mt::Vertex, incoming: Option<(mt::Edge, mt::Face)>, outgoing: Option<(mt::Edge, mt::Face)> },
+    /// Rounded: each strip's own side edge, and the sector turning one into the other (in
+    /// pieces of less than a half turn).
+    Round { incoming: mt::Edge, outgoing: mt::Edge, sector: Vec<mt::Face> },
+}
+
+impl Joint {
+    fn new(a: Option<&Strip>, b: Option<&Strip>, mode: &RuledMode, corners: RuledCorners, eps: f64) -> Result<Joint> {
+        let side = |s: &Strip, e: &End, from_start: bool| {
+            let v = if from_start { s.base.front().clone() } else { s.base.back().clone() };
+            let top = mt::Vertex::new(p3(e.top));
+            mt::Edge::new_unchecked(&v, &top, mt::Curve::Line(mt::Line(v.point(), top.point())))
+        };
+        let (a, b) = match (a, b) {
+            (Some(a), Some(b)) => (a, b),
+            (Some(a), None) => return Ok(Joint::Shared(side(a, &a.end, false))),
+            (None, Some(b)) => return Ok(Joint::Shared(side(b, &b.start, true))),
+            (None, None) => return Err(KernelError::Failed("ruled surface: an empty joint".into())),
+        };
+        let (ea, eb) = (&a.end, &b.start);
+        let vertex = a.base.back().clone();
+        if (ea.ruling - eb.ruling).len() <= SAME_RULING {
+            let top = mt::Vertex::new(p3((ea.top + eb.top) * 0.5));
+            return Ok(Joint::Shared(mt::Edge::new_unchecked(&vertex, &top, mt::Curve::Line(mt::Line(vertex.point(), top.point())))));
+        }
+        // Where the far edges, carried on straight, meet: λ along the incoming one past its
+        // end, μ along the outgoing one past its start.
+        let meet = || -> Option<(Vec3, f64, f64)> {
+            let (p, q, u, v) = (ea.top, eb.top, ea.tangent, eb.tangent);
+            let w = p - q;
+            let (uu, uv, vv, uw, vw) = (u.dot(u), u.dot(v), v.dot(v), u.dot(w), v.dot(w));
+            let den = uu * vv - uv * uv;
+            if den < 1e-12 {
+                return None;
+            }
+            let (lam, mu) = ((uv * vw - vv * uw) / den, (uu * vw - uv * uw) / den);
+            let (x, y) = (p + u * lam, q + v * mu);
+            (x.dist(y) <= eps * 100.0 && lam.abs() < 1e3 * (1.0 + ea.at.dist(ea.top))).then_some(((x + y) * 0.5, lam, mu))
+        };
+        // An inside corner (the strips overlap) is cut back where the far edges meet; that needs
+        // straight far edges.
+        let inside = eb.ruling.dot(ea.tangent) - ea.ruling.dot(eb.tangent) < -1e-9;
+        let corner_at = vertex.point();
+        let refuse = |what: &str| KernelError::Invalid(format!("{what} at the corner at {:?}", from_p3(corner_at)));
+        if corners == RuledCorners::Mitre || inside {
+            let (m, lam, mu) = meet().ok_or_else(|| refuse("the strips' far edges don't meet: try round corners,"))?;
+            let convex = lam > 0.0 && mu < 0.0;
+            let concave = lam < 0.0 && mu > 0.0;
+            if !(convex || concave) {
+                return Err(refuse("the strips cross"));
+            }
+            if concave && !(a.line && b.line) {
+                return Err(refuse("not supported yet: cutting back a curved strip"));
+            }
+            let mv = mt::Vertex::new(p3(m));
+            let edge = mt::Edge::new_unchecked(&vertex, &mv, mt::Curve::Line(mt::Line(vertex.point(), mv.point())));
+            // A strip that isn't a plane keeps its side edge and gets a triangle up to the
+            // mitre, in its tangent plane there.
+            let triangle = |s: &Strip, e: &End, from_start: bool| -> Option<(mt::Edge, mt::Face)> {
+                if s.planar {
+                    return None;
+                }
+                let own = side(s, e, from_start);
+                let top = own.back().clone();
+                let rim = mt::Edge::new_unchecked(&mv, &top, mt::Curve::Line(mt::Line(mv.point(), top.point())));
+                let (wire, surface): (Vec<mt::Edge>, _) = if from_start {
+                    (vec![own.clone(), rim.inverse(), edge.inverse()], plane_through(e.at, e.top, m))
+                } else {
+                    (vec![edge.clone(), rim, own.inverse()], plane_through(e.at, m, e.top))
+                };
+                Some((own, mt::Face::new_unchecked(vec![wire.into()], surface)))
+            };
+            let incoming = triangle(a, ea, false);
+            let outgoing = triangle(b, eb, true);
+            return Ok(Joint::Mitre { edge, m: mv, incoming, outgoing });
+        }
+        // Rounded: the incoming ruling turned into the outgoing one about an axis both keep
+        // the same angle to (the reference direction, or the faces' normal: a cone), else
+        // about the axis square to both (a flat sector).
+        let mut axes: Vec<Vec3> = Vec::new();
+        if let RuledMode::Angle { reference: Some(r), .. } = mode {
+            axes.push(*r);
+        }
+        if let Some(n) = (ea.normal + eb.normal).normalized() {
+            axes.push(n);
+        }
+        let flat = |x: Vec3, ax: Vec3| x - ax * x.dot(ax);
+        let axis = axes
+            .into_iter()
+            .find(|ax| {
+                (ea.ruling.dot(*ax) - eb.ruling.dot(*ax)).abs() <= 1e-9 && flat(ea.ruling, *ax).len() > 1e-6 && flat(eb.ruling, *ax).len() > 1e-6
+            })
+            .or_else(|| ea.ruling.cross(eb.ruling).normalized())
+            .ok_or_else(|| refuse("the strips turn back on each other"))?;
+        let (pa, pb) = (flat(ea.ruling, axis), flat(eb.ruling, axis));
+        let turn = pa.cross(pb).dot(axis).atan2(pa.dot(pb));
+        let (axis, turn) = if turn < 0.0 { (-axis, -turn) } else { (axis, turn) };
+        if !(turn > 1e-9 && turn < std::f64::consts::PI - 1e-6) {
+            return Err(refuse("the strips turn back on each other"));
+        }
+        let incoming = side(a, ea, false);
+        // Swept about the vertex (on the axis, so the sector closes there in a point).
+        let mut sector: Vec<mt::Face> = mt::builder::cone(&vec![incoming.clone()].into(), v3(axis), mt::Rad(turn)).into_iter().collect();
+        let edges: Vec<mt::Edge> =
+            sector.iter().flat_map(|f| f.boundaries().into_iter().flat_map(|w| w.edge_iter().cloned().collect::<Vec<_>>())).collect();
+        // The sector runs down the incoming side (the strip runs up it).
+        if edges.iter().any(|e| e.id() == incoming.id() && e.front().id() == vertex.id()) {
+            for f in &mut sector {
+                f.invert();
+            }
+        }
+        // Its other side: the edge from the vertex that only one piece of it has.
+        let uses = |id: mt::EdgeID| edges.iter().filter(|e| e.id() == id).count();
+        let outgoing = edges
+            .iter()
+            .find(|e| e.id() != incoming.id() && uses(e.id()) == 1 && (e.front().id() == vertex.id() || e.back().id() == vertex.id()))
+            .map(|e| if e.front().id() == vertex.id() { e.clone() } else { e.inverse() })
+            .ok_or_else(|| KernelError::Failed("ruled surface: a round corner's side".into()))?;
+        Ok(Joint::Round { incoming, outgoing, sector })
+    }
+
+    /// The edges a strip runs up from the joint's vertex (in order), and the vertex its far edge
+    /// starts or ends at.
+    fn side(&self, which: Side, s: &Strip) -> (Vec<mt::Edge>, mt::Vertex) {
+        match self {
+            Joint::Shared(e) => (vec![e.clone()], e.back().clone()),
+            Joint::Round { incoming, outgoing, .. } => {
+                let e = if which == Side::In { incoming } else { outgoing };
+                (vec![e.clone()], e.back().clone())
+            }
+            Joint::Mitre { edge, m, incoming, outgoing } => {
+                let own = if which == Side::In { incoming } else { outgoing };
+                if let Some((e, _)) = own {
+                    return (vec![e.clone()], e.back().clone());
+                }
+                if s.line {
+                    return (vec![edge.clone()], m.clone());
+                }
+                // A plane under a curved far edge: on along the mitre's far edge to it.
+                let e = if which == Side::In { &s.end } else { &s.start };
+                let top = mt::Vertex::new(p3(e.top));
+                let rim = mt::Edge::new_unchecked(m, &top, mt::Curve::Line(mt::Line(m.point(), top.point())));
+                (vec![edge.clone(), rim], top)
+            }
+        }
+    }
+
+    /// The joint's own faces: a round corner's sector, a mitre's triangles.
+    fn corner_faces(&self) -> Vec<&mt::Face> {
+        match self {
+            Joint::Shared(_) => Vec::new(),
+            Joint::Round { sector, .. } => sector.iter().collect(),
+            Joint::Mitre { incoming, outgoing, .. } => incoming.iter().chain(outgoing).map(|(_, f)| f).collect(),
+        }
+    }
+}
+
+/// The plane through three points, its normal (b − a) × (c − a).
+fn plane_through(a: Vec3, b: Vec3, c: Vec3) -> mt::Surface {
+    mt::Surface::Plane(mt::Plane::new(p3(a), p3(b), p3(c)))
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+    use std::f64::consts::{FRAC_1_SQRT_2, PI};
+
+    use solidcraft_geom::{Loop2, Plane, Region2, Vec2};
+
+    use super::*;
+    use crate::history::FaceOrigin;
+    use crate::{FaceSurface, box_solid, cylinder, face_surface, measure};
+
+    fn rel(a: f64, b: f64) -> f64 {
+        (a - b).abs() / b.abs().max(1e-9)
+    }
+    fn ruled(mode: RuledMode, distance: f64, face: Vec3) -> Ruled {
+        Ruled { distance, mode, flip: false, corners: RuledCorners::Mitre, face: Some(face) }
+    }
+    fn area(b: &Body) -> f64 {
+        measure(b).unwrap().area
+    }
+    /// How many faces use each edge of a body.
+    fn uses(b: &Body) -> HashMap<mt::EdgeID, usize> {
+        let mut m = HashMap::new();
+        for e in b.solid.face_iter().flat_map(|f| f.boundaries().into_iter().flat_map(|w| w.edge_iter().map(|e| e.id()).collect::<Vec<_>>())) {
+            *m.entry(e).or_default() += 1;
+        }
+        m
+    }
+    fn shared(b: &Body) -> usize {
+        uses(b).values().filter(|n| **n == 2).count()
+    }
+
+    /// A straight edge (a box's top front edge, 10 long) with a strip 4 wide in every mode: a
+    /// 10 × 4 plane each time, leaving the edge the way the mode says.
+    #[test]
+    fn a_straight_edge_in_every_mode() {
+        let b = box_solid(Vec3::ZERO, Vec3::new(10.0, 10.0, 10.0)).unwrap();
+        let (edge, top, front) = ([Vec3::new(5.0, 0.0, 10.0)], Vec3::new(5.0, 5.0, 10.0), Vec3::new(5.0, 0.0, 5.0));
+        let (s30, c30) = (30f64.to_radians().sin(), 30f64.to_radians().cos());
+        let (s10, c10) = (10f64.to_radians().sin(), 10f64.to_radians().cos());
+        let cases: [(Ruled, Vec3, Vec3); 7] = [
+            // Up the top's normal.
+            (ruled(RuledMode::Normal, 4.0, top), Vec3::new(0.0, 0.0, 10.0), Vec3::new(10.0, 0.0, 14.0)),
+            // Out across the top's edge, continuing it.
+            (ruled(RuledMode::Tangent, 4.0, top), Vec3::new(0.0, -4.0, 10.0), Vec3::new(10.0, 0.0, 10.0)),
+            // 30° from the top's normal, leaning away from it.
+            (
+                ruled(RuledMode::Angle { angle: 30f64.to_radians(), reference: None }, 4.0, top),
+                Vec3::new(0.0, -4.0 * s30, 10.0),
+                Vec3::new(10.0, 0.0, 10.0 + 4.0 * c30),
+            ),
+            // A 10° draft from the pull direction (+Z) off the front face's top edge: out from
+            // the part.
+            (
+                ruled(RuledMode::Angle { angle: 10f64.to_radians(), reference: Some(Vec3::Z) }, 4.0, front),
+                Vec3::new(0.0, -4.0 * s10, 10.0),
+                Vec3::new(10.0, 0.0, 10.0 + 4.0 * c10),
+            ),
+            // Along a fixed vector (not a unit one).
+            (
+                ruled(RuledMode::Direction(Vec3::new(0.0, -3.0, 3.0)), 4.0, top),
+                Vec3::new(0.0, -4.0 * FRAC_1_SQRT_2, 10.0),
+                Vec3::new(10.0, 0.0, 10.0 + 4.0 * FRAC_1_SQRT_2),
+            ),
+            // The front face's normal (-Y), and flipped: down the top's normal.
+            (ruled(RuledMode::Normal, 4.0, front), Vec3::new(0.0, -4.0, 10.0), Vec3::new(10.0, 0.0, 10.0)),
+            (Ruled { flip: true, ..ruled(RuledMode::Normal, 4.0, top) }, Vec3::new(0.0, 0.0, 6.0), Vec3::new(10.0, 0.0, 10.0)),
+        ];
+        for (r, lo, hi) in cases {
+            let s = ruled_surface(&b, &edge, &r).unwrap();
+            let m = measure(&s).unwrap();
+            assert!(s.is_surface() && s.face_count() == 1, "{r:?}");
+            assert!(rel(m.area, 40.0) < 1e-9, "{r:?}: {}", m.area);
+            assert!(m.bbox.min.dist(lo) < 1e-9 && m.bbox.max.dist(hi) < 1e-9, "{r:?}: {:?}", m.bbox);
+            assert!(matches!(face_surface(&s, 0), Some(FaceSurface::Plane { .. })), "{r:?}");
+        }
+    }
+
+    /// A circle (a cylinder's top rim, radius 10, picked all round) with a strip 4 wide in every
+    /// mode, from the top face: a cylinder 2π·10·4 up its normal, a ring π(14² − 10²) across
+    /// it, a cone π·4·(2·10 + 4 sin 30°) at 30°, and the cylinder again along +Z. From the side
+    /// face instead, its normal makes the ring and its tangent the cylinder.
+    #[test]
+    fn a_circle_in_every_mode() {
+        let c = cylinder(Vec3::ZERO, Vec3::Z, 10.0, 20.0).unwrap();
+        let rim = [Vec3::new(10.0, 0.0, 20.0), Vec3::new(0.0, 10.0, 20.0), Vec3::new(-10.0, 0.0, 20.0), Vec3::new(0.0, -10.0, 20.0)];
+        let (top, side) = (Vec3::new(0.0, 0.0, 20.0), Vec3::new(10.0, 0.0, 10.0));
+        let cylinder_area = 2.0 * PI * 10.0 * 4.0;
+        let ring = PI * (14.0 * 14.0 - 100.0);
+        let cases = [
+            (ruled(RuledMode::Normal, 4.0, top), cylinder_area, "cylinder"),
+            (ruled(RuledMode::Tangent, 4.0, top), ring, "plane"),
+            (ruled(RuledMode::Angle { angle: 30f64.to_radians(), reference: None }, 4.0, top), PI * 4.0 * 22.0, "cone"),
+            (ruled(RuledMode::Direction(Vec3::new(0.0, 0.0, 2.0)), 4.0, top), cylinder_area, "cylinder"),
+            (ruled(RuledMode::Normal, 4.0, side), ring, "plane"),
+            (ruled(RuledMode::Tangent, 4.0, side), cylinder_area, "cylinder"),
+        ];
+        for (r, want, kind) in cases {
+            let s = ruled_surface(&c, &rim, &r).unwrap();
+            assert!(rel(area(&s), want) < 2e-3, "{r:?}: {} vs {want}", area(&s)); // (measured on meshes)
+            for i in 0..s.face_count() {
+                let got = face_surface(&s, i);
+                let ok = match kind {
+                    "cylinder" => matches!(got, Some(FaceSurface::Cylinder { radius, .. }) if (radius - 10.0).abs() < 1e-6),
+                    "cone" => matches!(got, Some(FaceSurface::Cone { half_angle, .. }) if (half_angle - 30f64.to_radians()).abs() < 1e-6),
+                    _ => matches!(got, Some(FaceSurface::Plane { .. })),
+                };
+                assert!(ok, "{r:?}: {got:?}");
+            }
+            // The strips of the rim's arcs share their side edges: the strip closes round.
+            assert_eq!(shared(&s), s.face_count(), "{r:?}");
+        }
+    }
+
+    /// A closed chain round a box top (10 × 10), 2 wide: corners join with no gap or overlap.
+    /// Up the normal the strips share their corner edges (area 4·10·2). Across the top, mitred
+    /// they make a 14 × 14 frame less the top; rounded, 4·10·2 plus a quarter disc at each
+    /// corner. At 45° mitred, four trapezoids 2·(10 + √2); rounded, quarter cones π·√2·2.
+    /// Stitching the result sews nothing more: every join is already shared.
+    #[test]
+    fn a_closed_chain_round_a_box_top() {
+        let b = box_solid(Vec3::ZERO, Vec3::new(10.0, 10.0, 10.0)).unwrap();
+        let rim = [Vec3::new(5.0, 0.0, 10.0), Vec3::new(10.0, 5.0, 10.0), Vec3::new(5.0, 10.0, 10.0), Vec3::new(0.0, 5.0, 10.0)];
+        let top = Vec3::new(5.0, 5.0, 10.0);
+        let round = |m: RuledMode| Ruled { corners: RuledCorners::Round, ..ruled(m, 2.0, top) };
+        let angle = RuledMode::Angle { angle: PI / 4.0, reference: None };
+        let h = 2.0 * FRAC_1_SQRT_2;
+        let cases = [
+            (ruled(RuledMode::Normal, 2.0, top), 80.0, 4, 4),
+            (ruled(RuledMode::Tangent, 2.0, top), 14.0 * 14.0 - 100.0, 4, 4),
+            (round(RuledMode::Tangent), 80.0 + PI * 4.0, 12, 12),
+            (ruled(angle, 2.0, top), 80.0 + 4.0 * 2.0 * h, 4, 4),
+            (round(angle), 80.0 + PI * h * 2.0, 12, 12),
+        ];
+        for (r, want, faces, joins) in cases {
+            let s = ruled_surface(&b, &rim, &r).unwrap();
+            assert!(rel(area(&s), want) < 2e-3, "{r:?}: {} vs {want}", area(&s)); // (measured on meshes)
+            assert_eq!((s.face_count(), shared(&s)), (faces, joins), "{r:?}");
+            // The strips stand on the box's own edges.
+            let own: std::collections::HashSet<mt::EdgeID> = b.solid.edge_iter().map(|e| e.id()).collect();
+            assert_eq!(uses(&s).keys().filter(|e| own.contains(e)).count(), 4);
+            let sewn = crate::stitch(&[&s], 0.0).unwrap();
+            assert_eq!((sewn.face_count(), shared(&sewn), uses(&sewn).len()), (faces, joins, uses(&s).len()), "{r:?}");
+        }
+    }
+
+    /// An inside corner (an L-shaped prism's top: 20 × 10 and 10 × 10) is cut back, mitred or
+    /// rounded: across the top 2 wide, the mitred frame is 24 × 24 less a 10 × 10 notch less
+    /// the L (476 − 300); rounded, the five outside corners are quarter discs and the inside
+    /// one stays mitred (80·2 − 2² + 5·π·2²/4).
+    #[test]
+    fn an_inside_corner_is_cut_back() {
+        let outer = Loop2::polygon(&[
+            Vec2::ZERO,
+            Vec2::new(20.0, 0.0),
+            Vec2::new(20.0, 10.0),
+            Vec2::new(10.0, 10.0),
+            Vec2::new(10.0, 20.0),
+            Vec2::new(0.0, 20.0),
+        ]);
+        let ell = crate::extrude(&Plane::XY, &[Region2 { outer, holes: vec![] }], 0.0, 10.0).unwrap().pop().unwrap();
+        let rim: Vec<Vec3> =
+            [(10.0, 0.0), (20.0, 5.0), (15.0, 10.0), (10.0, 15.0), (5.0, 20.0), (0.0, 10.0)].iter().map(|(x, y)| Vec3::new(*x, *y, 10.0)).collect();
+        let top = Vec3::new(5.0, 5.0, 10.0);
+        let mitre = ruled_surface(&ell, &rim, &ruled(RuledMode::Tangent, 2.0, top)).unwrap();
+        assert!(rel(area(&mitre), 176.0) < 1e-9, "{}", area(&mitre));
+        let round = ruled_surface(&ell, &rim, &Ruled { corners: RuledCorners::Round, ..ruled(RuledMode::Tangent, 2.0, top) }).unwrap();
+        let want = 156.0 + 5.0 * PI;
+        assert!(rel(area(&round), want) < 2e-3, "{} vs {want}", area(&round)); // (measured on meshes)
+    }
+
+    /// A curved edge a cut left (a box side cut by a cylinder of radius 40: an arc of it on the
+    /// side face, 2·40·asin(14/40) long), with strips 3 wide out of that face and continuing
+    /// the cut: 3 times its length each.
+    #[test]
+    fn an_edge_a_cut_left() {
+        let b = box_solid(Vec3::new(-14.0, -14.0, 0.0), Vec3::new(14.0, 14.0, 20.0)).unwrap();
+        let tool = cylinder(Vec3::new(0.0, -60.0, 50.0), Vec3::Y, 40.0, 120.0).unwrap();
+        let cup = crate::boolean(&b, &tool, crate::BoolOp::Cut).unwrap().unwrap();
+        let z = 50.0 - (1600.0f64 - 0.0).sqrt();
+        let (rim, side, cut) = ([Vec3::new(0.0, -14.0, z)], Vec3::new(0.0, -14.0, 5.0), Vec3::new(0.0, 0.0, z));
+        let want = 3.0 * 80.0 * (14.0f64 / 40.0).asin();
+        for r in [ruled(RuledMode::Normal, 3.0, side), ruled(RuledMode::Tangent, 3.0, cut)] {
+            let s = ruled_surface(&cup, &rim, &r).unwrap();
+            assert!(rel(area(&s), want) < 2e-3, "{r:?}: {} vs {want}", area(&s)); // (measured on meshes)
+            let bb = measure(&s).unwrap().bbox;
+            assert!((bb.min.y + 17.0).abs() < 1e-6 && (bb.max.y + 14.0).abs() < 1e-6, "{r:?}: {bb:?}");
+        }
+    }
+
+    /// Off a doubly curved face (a saddle patch over a cup's rim) its normal turns along a
+    /// straight edge: the strip is a fitted ruled B-spline, its rulings square to the edge, so
+    /// it reaches exactly 3 from the edge's line (within the fit) and covers it end to end.
+    #[test]
+    fn a_strip_off_a_curved_face_is_fitted() {
+        let b = box_solid(Vec3::new(-14.0, -14.0, 0.0), Vec3::new(14.0, 14.0, 20.0)).unwrap();
+        let tool = cylinder(Vec3::new(0.0, -60.0, 50.0), Vec3::Y, 40.0, 120.0).unwrap();
+        let cup = crate::boolean(&b, &tool, crate::BoolOp::Cut).unwrap().unwrap();
+        let z = |x: f64| 50.0 - (1600.0 - x * x).sqrt();
+        let rim = [Vec3::new(14.0, 0.0, z(14.0)), Vec3::new(0.0, 14.0, z(0.0)), Vec3::new(-14.0, 0.0, z(-14.0)), Vec3::new(0.0, -14.0, z(0.0))];
+        let cover = crate::patch_edges(&cup, &rim).unwrap();
+        let edge = [Vec3::new(14.0, 0.0, z(14.0))];
+        let s = ruled_surface(&cover, &edge, &ruled(RuledMode::Normal, 3.0, Vec3::new(0.0, 0.0, 12.0))).unwrap();
+        assert!(s.face_count() == 1 && face_surface(&s, 0).is_none(), "{:?}", face_surface(&s, 0));
+        let mesh = s.tessellate(0.01).unwrap();
+        let from_line = |p: &Vec3| Vec3::new(p.x - 14.0, 0.0, p.z - z(14.0)).len();
+        let far = mesh.positions.iter().map(from_line).fold(0.0, f64::max);
+        assert!((far - 3.0).abs() < 2e-3, "{far}");
+        let bb = measure(&s).unwrap().bbox;
+        assert!((bb.min.y + 14.0).abs() < 1e-3 && (bb.max.y - 14.0).abs() < 1e-3, "{bb:?}");
+    }
+
+    /// Each strip is made in place of the edge it stands on; a corner face in place of the two
+    /// edges meeting at it.
+    #[test]
+    fn strips_come_from_their_edges() {
+        let b = box_solid(Vec3::ZERO, Vec3::new(10.0, 10.0, 10.0)).unwrap();
+        let rim = [Vec3::new(5.0, 0.0, 10.0), Vec3::new(10.0, 5.0, 10.0)];
+        let r = Ruled { corners: RuledCorners::Round, ..ruled(RuledMode::Tangent, 2.0, Vec3::new(5.0, 5.0, 10.0)) };
+        let s = ruled_surface(&b, &rim, &r).unwrap();
+        let h = s.history().unwrap();
+        let edges = |k: usize| h.faces.get(k).unwrap().origins.iter().filter(|o| matches!(o, FaceOrigin::Edge { operand: 0, .. })).count();
+        let counts: Vec<usize> = (0..s.face_count()).map(edges).collect();
+        assert_eq!(counts.iter().filter(|n| **n == 1).count(), 2, "{counts:?}");
+        assert!(counts.iter().all(|n| *n == 1 || *n == 2), "{counts:?}");
+    }
+
+    /// Hostile settings are refused, never a panic: a zero, negative or non-finite distance, a
+    /// non-finite angle, no direction, a direction along the edge, edges that branch.
+    #[test]
+    fn hostile_settings_are_refused() {
+        let b = box_solid(Vec3::ZERO, Vec3::new(10.0, 10.0, 10.0)).unwrap();
+        let edge = [Vec3::new(5.0, 0.0, 10.0)];
+        let top = Vec3::new(5.0, 5.0, 10.0);
+        for d in [0.0, -1.0, f64::NAN, f64::INFINITY, 1e300] {
+            assert!(ruled_surface(&b, &edge, &ruled(RuledMode::Normal, d, top)).is_err(), "{d}");
+        }
+        for m in [
+            RuledMode::Angle { angle: f64::NAN, reference: None },
+            RuledMode::Angle { angle: 0.5, reference: Some(Vec3::ZERO) },
+            RuledMode::Angle { angle: 0.5, reference: Some(Vec3::X) },
+            RuledMode::Direction(Vec3::ZERO),
+            RuledMode::Direction(Vec3::X),
+            RuledMode::Direction(Vec3::new(f64::NAN, 0.0, 1.0)),
+        ] {
+            assert!(ruled_surface(&b, &edge, &ruled(m, 2.0, top)).is_err(), "{m:?}");
+        }
+        // Three edges meeting at a corner branch.
+        let corner = [Vec3::new(5.0, 0.0, 10.0), Vec3::new(0.0, 5.0, 10.0), Vec3::new(0.0, 0.0, 5.0)];
+        assert!(ruled_surface(&b, &corner, &ruled(RuledMode::Normal, 2.0, top)).is_err());
+        assert!(ruled_surface(&b, &[], &ruled(RuledMode::Normal, 2.0, top)).is_err());
+        assert!(ruled_surface(&b, &[Vec3::new(500.0, 0.0, 0.0)], &ruled(RuledMode::Normal, 2.0, top)).is_err());
+    }
+}

crates/kernel/src/surfaces.rs

@@ -415,6 +415,17 @@ pub fn patch_edges(body: &Body, at: &[Vec3]) -> Result<Body> {
 /// The edges of `body` picked by points on them, chained into one closed loop (each turned to
 /// run along it). Call it under [`guard`]: sampling an intersection curve can fail in truck.
 pub(crate) fn picked_loop(body: &Body, at: &[Vec3]) -> Result<Vec<mt::Edge>> {
+    match picked_chain(body, at)? {
+        (chain, true) => Ok(chain),
+        (_, false) => Err(KernelError::Invalid("the edges do not form a closed loop".into())),
+    }
+}
+
+/// The edges of `body` picked by points on them, chained end to end (each turned to run along
+/// the chain), and whether the chain closes: a closed loop starts with the last edge picked; an
+/// open chain runs from the free end met first in pick order. Edges that branch, or form more
+/// than one chain, are refused. Call it under [`guard`], as [`picked_loop`].
+pub(crate) fn picked_chain(body: &Body, at: &[Vec3]) -> Result<(Vec<mt::Edge>, bool)> {
     let mut edges: Vec<mt::Edge> = Vec::new();
     for p in at {
         let e = edge_near(body, *p).ok_or_else(|| KernelError::Invalid(format!("no edge at {p:?}")))?;
@@ -422,25 +433,40 @@ pub(crate) fn picked_loop(body: &Body, at: &[Vec3]) -> Result<Vec<mt::Edge>> {
             edges.push(e);
         }
     }
+    let mut uses: HashMap<mt::VertexID, usize> = HashMap::new();
+    for e in &edges {
+        *uses.entry(e.front().id()).or_default() += 1;
+        *uses.entry(e.back().id()).or_default() += 1;
+    }
+    if uses.values().any(|n| *n > 2) {
+        return Err(KernelError::Invalid("the edges branch: pick one chain".into()));
+    }
+    let free = |v: &mt::Vertex| uses.get(&v.id()) == Some(&1);
+    let open_end = edges.iter().find_map(|e| [e.front(), e.back()].into_iter().find(|v| free(v)).cloned());
     let mut pool = edges;
-    let first = pool.pop().ok_or_else(|| KernelError::Invalid("no edges".into()))?;
+    let (first, closed) = match &open_end {
+        Some(v) => {
+            let k = pool.iter().position(|e| e.front().id() == v.id() || e.back().id() == v.id());
+            let e = k.map(|k| pool.remove(k)).ok_or_else(|| KernelError::Invalid("no edges".into()))?;
+            (if e.front().id() == v.id() { e } else { e.inverse() }, false)
+        }
+        None => (pool.pop().ok_or_else(|| KernelError::Invalid("no edges".into()))?, true),
+    };
     let start = first.front().id();
     let mut at_v = first.back().clone();
     let mut chain = vec![first];
-    while at_v.id() != start {
+    while !(closed && at_v.id() == start) {
-        let k = pool
+        let Some(k) = pool.iter().position(|e| e.front().id() == at_v.id() || e.back().id() == at_v.id()) else { break };
-            .iter()
-            .position(|e| e.front().id() == at_v.id() || e.back().id() == at_v.id())
-            .ok_or_else(|| KernelError::Invalid("the edges do not form a closed loop".into()))?;
         let e = pool.remove(k);
         let e = if e.front().id() == at_v.id() { e } else { e.inverse() };
         at_v = e.back().clone();
         chain.push(e);
     }
     if !pool.is_empty() {
-        return Err(KernelError::Invalid("the edges form more than one loop".into()));
+        let what = if closed { "the edges form more than one loop" } else { "the edges form more than one chain" };
+        return Err(KernelError::Invalid(what.into()));
     }
-    Ok(chain)
+    Ok((chain, closed))
 }
 
 /// Faces of a body copied out as a surface body (faces picked by points on them). Its history is
@@ -695,10 +721,24 @@ fn map_pt(off: &Offset, p: mt::Point3, d: f64) -> mt::Point3 {
 /// A curve moved by an offset (control points mapped; exact for lines, and for circles square
 /// to a cylinder's axis or in a plane).
 pub(crate) fn map_curve(off: &Offset, c: &mt::Curve, d: f64) -> Result<mt::Curve> {
-    Ok(match c {
+    if let Some(moved) = map_control_points(c, |p| off.map(p, d)) {
-        mt::Curve::Line(l) => mt::Curve::Line(mt::Line(map_pt(off, l.0, d), map_pt(off, l.1, d))),
+        return Ok(moved);
+    }
+    // Anything else: a cubic through moved samples.
+    let (t0, t1) = c.range_tuple();
+    let pts: Vec<Vec3> = (0..=32).map(|k| off.map(from_p3(c.subs(t0 + (t1 - t0) * k as f64 / 32.0)), d)).collect();
+    Ok(mt::Curve::BSplineCurve(crate::build::interpolate_cubic(&pts).ok_or_else(|| KernelError::Failed("offset edge".into()))?))
+}
+
+/// A line, B-spline or NURBS curve with its control points mapped by `f` (the exact image of
+/// the curve under an affine `f`); `None` for a curve without control points (an
+/// intersection curve).
+pub(crate) fn map_control_points(c: &mt::Curve, f: impl Fn(Vec3) -> Vec3) -> Option<mt::Curve> {
+    let map = |p: mt::Point3| p3(f(from_p3(p)));
+    Some(match c {
+        mt::Curve::Line(l) => mt::Curve::Line(mt::Line(map(l.0), map(l.1))),
         mt::Curve::BSplineCurve(b) => {
-            let pts: Vec<mt::Point3> = b.control_points().iter().map(|p| map_pt(off, *p, d)).collect();
+            let pts: Vec<mt::Point3> = b.control_points().iter().map(|p| map(*p)).collect();
             mt::Curve::BSplineCurve(mt::BSplineCurve::new(b.knot_vec().clone(), pts))
         }
         mt::Curve::NurbsCurve(n) => {
@@ -708,18 +748,13 @@ pub(crate) fn map_curve(off: &Offset, c: &mt::Curve, d: f64) -> Result<mt::Curve
                 .iter()
                 .map(|h| {
                     let w = h.w;
-                    let q = map_pt(off, mt::Point3::new(h.x / w, h.y / w, h.z / w), d);
+                    let q = map(mt::Point3::new(h.x / w, h.y / w, h.z / w));
                     mt::Vector4::new(q.x * w, q.y * w, q.z * w, w)
                 })
                 .collect();
             mt::Curve::NurbsCurve(mt::NurbsCurve::new(mt::BSplineCurve::new(nb.knot_vec().clone(), pts)))
         }
-        other => {
+        mt::Curve::IntersectionCurve(_) => return None,
-            // Anything else: a cubic through moved samples.
-            let (t0, t1) = other.range_tuple();
-            let pts: Vec<Vec3> = (0..=32).map(|k| off.map(from_p3(other.subs(t0 + (t1 - t0) * k as f64 / 32.0)), d)).collect();
-            mt::Curve::BSplineCurve(crate::build::interpolate_cubic(&pts).ok_or_else(|| KernelError::Failed("offset edge".into()))?)
-        }
     })
 }
 

crates/ui-egui/src/dialogs_surface.rs

@@ -1,10 +1,10 @@
 //! Dialogs for the surface tools and face splitting (#19): Surface Extrude, Revolve, Sweep and
-//! Loft, Patch, Stitch, Thicken, Extend, Trim, Untrim and Split Face. Each has a live preview and Edit Feature.
+//! Loft, Offset and Ruled Surface, Patch, Stitch, Thicken, Extend, Trim, Untrim and Split Face. Each has a live preview and Edit Feature.
 
 use serde_json::{Map, Value, json};
 use solidcraft_engine::Sel;
 use solidcraft_engine::doc::expr::Kind as ValueKind;
-use solidcraft_engine::doc::{AxisRef, Direction, FaceAt, FeatureKind, Mat, PlaneRef, ProfileSel};
+use solidcraft_engine::doc::{AxisRef, Direction, FaceAt, FeatureKind, Mat, PlaneRef, ProfileSel, RuledCorners, RuledMode};
 use solidcraft_engine::geom::Vec3;
 
 use crate::SolveApp;
@@ -34,6 +34,14 @@ pub enum Surf {
         distance: String,
         chain: bool,
     },
+    /// `mode`: an index into [`RULED_MODES`].
+    Ruled {
+        distance: String,
+        mode: usize,
+        angle: String,
+        flip: bool,
+        round: bool,
+    },
     Stitch {
         tolerance: String,
     },
@@ -69,6 +77,7 @@ impl Surf {
             Surf::Unstitch => "UNSTITCH",
             Surf::ReverseNormal => "REVERSE NORMAL",
             Surf::Offset { .. } => "OFFSET SURFACE",
+            Surf::Ruled { .. } => "RULED SURFACE",
             Surf::Stitch { .. } => "STITCH",
             Surf::ConvertMesh { .. } => "CONVERT MESH",
             Surf::Thicken { .. } => "THICKEN",
@@ -83,7 +92,9 @@ impl Surf {
     pub fn primary(&mut self) -> Option<(&'static str, ValueKind, &mut String)> {
         Some(match self {
             Surf::Thicken { thickness, .. } => ("Thickness", ValueKind::Length, thickness),
-            Surf::Extend { distance } | Surf::Extrude { distance, .. } | Surf::Offset { distance, .. } => ("Distance", ValueKind::Length, distance),
+            Surf::Extend { distance } | Surf::Extrude { distance, .. } | Surf::Offset { distance, .. } | Surf::Ruled { distance, .. } => {
+                ("Distance", ValueKind::Length, distance)
+            }
             Surf::Revolve { angle, .. } => ("Angle", ValueKind::Angle, angle),
             _ => return None,
         })
@@ -96,6 +107,9 @@ const UNTRIM_HOLES: [&str; 3] = ["All", "Picked", "None"];
 /// The sides a surface extrude goes to (labels, and the `direction` parameter).
 const EXTRUDE_SIDES: [(&str, &str); 3] = [("One Side", "positive"), ("Symmetric", "symmetric"), ("Flipped", "negative")];
 
+/// The ways a ruled surface leaves its edges (labels, and the `mode` parameter).
+const RULED_MODES: [(&str, &str); 4] = [("Normal", "normal"), ("Tangent", "tangent"), ("Angle", "angle"), ("Direction", "direction")];
+
 fn inputs(k: &Surf) -> Vec<SelInput> {
     match k {
         Surf::Extrude { .. } => vec![SelInput::new("Profiles or curves", PROFILES | CURVES, true)],
@@ -106,6 +120,9 @@ fn inputs(k: &Surf) -> Vec<SelInput> {
         Surf::Unstitch => vec![SelInput::new("Body, or faces to take out", BODIES | FACES, true)],
         Surf::ReverseNormal => vec![SelInput::new("Surface, or faces to turn over", BODIES | FACES, true)],
         Surf::Offset { .. } => vec![SelInput::new("Faces", FACES, true)],
+        Surf::Ruled { .. } => {
+            vec![SelInput::new("Edges", EDGES, true), SelInput::new("Reference face", FACES, false), SelInput::new("Direction", AXES | EDGES, false)]
+        }
         Surf::Stitch { .. } => vec![SelInput::new("Surfaces", BODIES, true)],
         Surf::ConvertMesh { .. } => vec![SelInput::new("Mesh body", BODIES, false)],
         Surf::Thicken { .. } => vec![SelInput::new("Surfaces", BODIES, true)],
@@ -131,6 +148,7 @@ pub fn start(_app: &SolveApp, id: &str) -> Option<(Kind, Vec<SelInput>)> {
         "surface.unstitch" => Surf::Unstitch,
         "surface.reverse_normal" => Surf::ReverseNormal,
         "surface.offset" => Surf::Offset { distance: "2 mm".into(), chain: false },
+        "surface.ruled" => Surf::Ruled { distance: "10 mm".into(), mode: 0, angle: "5 deg".into(), flip: false, round: false },
         "surface.stitch" => Surf::Stitch { tolerance: String::new() },
         "mesh.convert" => Surf::ConvertMesh { tolerance: "0.05 mm".into() },
         "surface.thicken" => Surf::Thicken { thickness: "2 mm".into(), symmetric: false, operation: 0 },
@@ -191,6 +209,27 @@ pub fn rows(ui: &mut egui::Ui, k: &mut Surf) -> bool {
             ui.checkbox(chain, "");
             ui.end_row();
         }
+        Surf::Ruled { distance, mode, angle, flip, round } => {
+            row_label(ui, "Distance");
+            enter |= field(ui, distance);
+            ui.end_row();
+            row_label(ui, "Type");
+            combo(ui, "ru_mode", &RULED_MODES.map(|(label, _)| label), mode);
+            ui.end_row();
+            if RULED_MODES.get(*mode).is_some_and(|(_, m)| *m == "angle") {
+                row_label(ui, "Angle");
+                enter |= field(ui, angle);
+                ui.end_row();
+            }
+            row_label(ui, "Corners");
+            let mut corner = usize::from(*round);
+            combo(ui, "ru_corners", &["Mitre", "Round"], &mut corner);
+            *round = corner == 1;
+            ui.end_row();
+            row_label(ui, "Flip");
+            ui.checkbox(flip, "");
+            ui.end_row();
+        }
         Surf::Extrude { distance, direction } => {
             row_label(ui, "Distance");
             enter |= field(ui, distance);
@@ -377,6 +416,45 @@ pub fn commands(app: &SolveApp, k: &Surf, inputs: &[SelInput], extra: &Map<Strin
             }
             ("surface.offset", p)
         }
+        Surf::Ruled { distance, mode, angle, flip, round } => {
+            need(0, "the edges to rule from")?;
+            let edge_body = |x: &Sel| if let Sel::Edge { body, .. } = x { Some(body.clone()) } else { None };
+            let body = items(inputs, 0).iter().find_map(edge_body).ok_or("pick edges of a body")?;
+            if items(inputs, 0).iter().any(|x| edge_body(x).as_ref() != Some(&body)) {
+                return Err("pick edges of one body".into());
+            }
+            let edges: Vec<Value> =
+                items(inputs, 0).iter().filter_map(|x| if let Sel::Edge { point, .. } = x { Some(pt(*point)) } else { None }).collect();
+            let mode = RULED_MODES.get(*mode).map_or("normal", |(_, m)| *m);
+            let mut p = json!({"body": body, "edges": edges, "distance": distance, "mode": mode});
+            if mode == "angle" {
+                p["angle"] = json!(angle);
+            }
+            if let Some(Sel::Face { body: fb, point, .. }) = items(inputs, 1).first() {
+                if *fb != body {
+                    return Err("the reference face must be on the edges' body".into());
+                }
+                p["face"] = pt(*point);
+            }
+            // A picked direction, else the one the feature was made with (Edit Feature).
+            let kept = extra.get("direction").and_then(|v| serde_json::from_value::<[f64; 3]>(v.clone()).ok()).map(|a| Vec3::new(a[0], a[1], a[2]));
+            let dir = match items(inputs, 2).first() {
+                Some(x) => Some(crate::dialogs::axis_of(app, x).ok_or("the direction must be an axis, a sketch line or a straight edge")?.1),
+                None => kept,
+            };
+            match (mode, dir) {
+                ("angle" | "direction", Some(d)) => p["direction"] = pt(d),
+                ("direction", None) => return Err("select a direction (an axis, a sketch line or a straight edge) first".into()),
+                _ => {}
+            }
+            if *flip {
+                p["flip"] = json!(true);
+            }
+            if *round {
+                p["corners"] = json!("round");
+            }
+            ("surface.ruled", p)
+        }
         Surf::Unstitch | Surf::ReverseNormal => {
             need(0, "a body or some of its faces")?;
             let (body, faces) = body_and_faces(items(inputs, 0))?;
@@ -465,7 +543,8 @@ pub fn commands(app: &SolveApp, k: &Surf, inputs: &[SelInput], extra: &Map<Strin
         }
     };
     if let Value::Object(m) = &mut p {
-        for (k, v) in extra {
+        // A ruled surface's kept direction is used above, or dropped with its mode.
+        for (k, v) in extra.iter().filter(|(k, _)| !(cmd == "surface.ruled" && k.as_str() == "direction")) {
             m.entry(k.clone()).or_insert_with(|| v.clone());
         }
     }
@@ -539,6 +618,30 @@ pub fn for_feature(app: &SolveApp, kind: &FeatureKind, frame: &Mat) -> Option<(K
         FeatureKind::SurfaceOffset { faces, distance, chain, .. } => {
             (Surf::Offset { distance: distance.clone(), chain: *chain }, vec![faces.iter().filter_map(|p| crate::dialogs::face_sel(s, *p)).collect()])
         }
+        FeatureKind::SurfaceRuled { edges, distance, mode, angle, direction, flip, corners, face, .. } => {
+            let k = Surf::Ruled {
+                distance: distance.clone(),
+                mode: match mode {
+                    RuledMode::Normal => 0,
+                    RuledMode::Tangent => 1,
+                    RuledMode::Angle => 2,
+                    RuledMode::Direction => 3,
+                },
+                angle: angle.clone().unwrap_or_else(|| "5 deg".into()),
+                flip: *flip,
+                round: *corners == RuledCorners::Round,
+            };
+            let mut ins = inputs(&k);
+            let fill = [edges.iter().filter_map(edge).collect(), face.and_then(|p| crate::dialogs::face_sel(s, p)).into_iter().collect()];
+            for (inp, items) in ins.iter_mut().zip(fill) {
+                inp.items = items;
+            }
+            let mut extra = Map::new();
+            if let Some(d) = direction {
+                extra.insert("direction".into(), pt(*d));
+            }
+            return Some((Kind::Surface(k), ins, extra));
+        }
         FeatureKind::Unstitch { body, faces } | FeatureKind::ReverseNormal { body, faces } => {
             let sels: Vec<Sel> = if faces.is_empty() {
                 vec![Sel::Body { name: body.clone() }]

crates/ui-egui/src/preselect_tests.rs

@@ -968,6 +968,46 @@ fn surface_loft_dialog_makes_a_section_per_sketch() {
     assert_eq!(back.inputs[0].items, vec![Sel::SketchCurve { id: "a".into() }, Sel::SketchCurve { id: "b".into() }]);
 }
 
+#[test]
+fn ruled_surface_dialog_takes_edges_a_face_and_a_direction() {
+    // A box top's front and right edges, ruled across the top 2 mm with round corners: two
+    // 10 × 2 strips and a quarter disc between them. Edit Feature brings it back; along a
+    // direction it needs one, and keeps the one it was made with.
+    let mut app = app_with(json!([{"command": "solid.box", "params": {"length": 10, "width": 10, "height": 10, "body_name": "Box"}}]));
+    let mut d = start(&mut app, vec![], "surface.ruled");
+    assert!(apply_commands(&app, &d).is_err(), "no edges yet");
+    let edge = |i: usize, p: Vec3| Sel::Edge { body: "Box".into(), index: i, point: p };
+    d.inputs[0].items = vec![edge(0, Vec3::new(5.0, 0.0, 10.0)), edge(1, Vec3::new(10.0, 5.0, 10.0))];
+    d.inputs[1].items = vec![Sel::Face { body: "Box".into(), index: 0, point: Vec3::new(5.0, 5.0, 10.0) }];
+    if let Kind::Surface(crate::dialogs_surface::Surf::Ruled { distance, mode, round, .. }) = &mut d.kind {
+        *distance = "2 mm".into();
+        *mode = 1;
+        *round = true;
+    }
+    let (id, p) = apply_commands(&app, &d).unwrap().remove(0);
+    assert_eq!(
+        (id.as_str(), &p["body"], &p["mode"], &p["corners"], &p["face"]),
+        ("surface.ruled", &json!("Box"), &json!("tangent"), &json!("round"), &json!([5.0, 5.0, 10.0])),
+        "{p}"
+    );
+    app.session.execute(&id, &p).unwrap();
+    let m = app.session.model.state().bodies.last().unwrap().mesh().measure();
+    let want = 40.0 + std::f64::consts::PI;
+    assert!((m.area - want).abs() < want * 2e-3, "{} vs {want}", m.area); // (measured on meshes)
+    let fid = app.session.doc.features.last().unwrap().id;
+    let mut back = crate::dialogs::for_feature(&app, fid, None).unwrap();
+    assert_eq!((back.inputs[0].items.len(), back.inputs[1].items.len()), (2, 1));
+    assert!(matches!(back.kind, Kind::Surface(crate::dialogs_surface::Surf::Ruled { mode: 1, round: true, .. })));
+    if let Kind::Surface(crate::dialogs_surface::Surf::Ruled { mode, .. }) = &mut back.kind {
+        *mode = 3;
+    }
+    assert!(apply_commands(&app, &back).is_err(), "a direction is needed");
+    back.inputs[2].items = vec![Sel::Axis { name: "Z".into() }];
+    // Edit Feature runs the command's parameters as an edit of the feature.
+    let (_, p) = apply_commands(&app, &back).unwrap().remove(0);
+    assert_eq!((&p["params"]["mode"], &p["params"]["direction"]), (&json!("direction"), &json!([0.0, 0.0, 1.0])), "{p}");
+}
+
 #[test]
 fn untrim_dialog_takes_a_face_its_holes_and_the_outer_boundary() {
     // A 40 × 20 × 2 plate with three holes: its top untrimmed (every hole) is the whole 800 mm²

crates/ui-egui/src/timeline.rs

@@ -19,6 +19,7 @@ pub(crate) fn icon_of(k: &FeatureKind) -> &'static str {
         FeatureKind::SurfaceSweep { .. } => "surface_sweep",
         FeatureKind::SurfaceLoft { .. } => "surface_loft",
         FeatureKind::SurfaceOffset { .. } => "surface_offset",
+        FeatureKind::SurfaceRuled { .. } => "ruled",
         FeatureKind::SurfaceUntrim { .. } => "untrim",
         FeatureKind::Revolve { .. } => "revolve",
         FeatureKind::Fillet { .. } => "fillet",

docs/features.md

@@ -1,6 +1,6 @@
 # Features
 
-SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **364 commands.** Planned (registered, not built yet): 5. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
+SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **365 commands.** Planned (registered, not built yet): 4. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
 
 ## Sketch (99)
 
@@ -146,7 +146,7 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 | Align | `solid.align` | SOLID › MODIFY |
 | Remove | `solid.remove` | SOLID › MODIFY |
 
-## Surfaces (13, 4 planned)
+## Surfaces (14, 3 planned)
 
 | Command | Id | Toolbar |
 |---|---|---|
@@ -160,7 +160,7 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 | Surface Sweep | `surface.sweep` | SURFACE › CREATE |
 | Surface Loft | `surface.loft` | SURFACE › CREATE |
 | Offset Surface | `surface.offset` | SURFACE › CREATE |
-| Ruled Surface *(planned: [#762](https://github.com/bherbruck/solidcraft/issues/762))* | `surface.ruled` | SURFACE › CREATE |
+| Ruled Surface | `surface.ruled` | SURFACE › CREATE |
 | Boundary Surface *(planned: [#763](https://github.com/bherbruck/solidcraft/issues/763))* | `surface.boundary` | SURFACE › CREATE |
 | Blend Surface *(planned: [#764](https://github.com/bherbruck/solidcraft/issues/764))* | `surface.blend` | SURFACE › CREATE |
 | Untrim | `surface.untrim` | SURFACE › MODIFY |