Offset Surface: faces copied out at a distance, exact or fitted (#758) (#872)

Offsets picked faces along their normals into a new surface body: planes and cylinders move exactly, other faces get a fitted B-spline within tolerance, and offsets that would fold over are refused. Adds the SurfaceOffset feature (noted under format 18), the surface.offset engine command and an Offset Surface dialog.

Closes #758.

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>

crates/doc/src/assembly.rs

@@ -237,9 +237,10 @@ impl FeatureKind {
                 }
             }
             FeatureKind::Chamfer { edges, .. } => edges.iter_mut().for_each(pt),
-            FeatureKind::Shell { faces, .. } | FeatureKind::OffsetFace { faces, .. } | FeatureKind::DeleteFace { faces, .. } => {
-                faces.iter_mut().for_each(pt)
-            }
+            FeatureKind::Shell { faces, .. }
+            | FeatureKind::OffsetFace { faces, .. }
+            | FeatureKind::DeleteFace { faces, .. }
+            | FeatureKind::SurfaceOffset { faces, .. } => faces.iter_mut().for_each(pt),
             FeatureKind::Draft { faces, neutral, pull, .. } => {
                 faces.iter_mut().for_each(pt);
                 map_plane_ref(m, neutral);

crates/doc/src/clipboard.rs

@@ -305,6 +305,7 @@ impl FeatureKind {
             | K::SplitFace { body, .. }
             | K::OffsetFace { body, .. }
             | K::DeleteFace { body, .. }
+            | K::SurfaceOffset { body, .. }
             | K::ReplaceFace { body, .. }
             | K::SheetFlange { body, .. }
             | K::SheetHem { body, .. }

crates/doc/src/document.rs

@@ -987,6 +987,19 @@ pub enum FeatureKind {
     SurfaceLoft {
         sections: Vec<SheetSection>,
     },
+    /// The faces at `faces` copied out at a signed `distance` along their normals as a new
+    /// surface body (0 copies them); `chain` takes each pick's whole smooth chain of faces;
+    /// fitted faces within `tolerance`.
+    SurfaceOffset {
+        faces: Vec<Vec3>,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        body: Option<String>,
+        distance: String,
+        #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+        chain: bool,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        tolerance: Option<String>,
+    },
     /// A planar surface body extended outward by `distance` past the edges through `edges`.
     SurfaceExtend {
         body: String,
@@ -1331,6 +1344,7 @@ impl FeatureKind {
             | K::Scale { .. }
             | K::OffsetFace { .. }
             | K::DeleteFace { .. }
+            | K::SurfaceOffset { .. }
             | K::BoundingSolid { .. }
             | K::ReplaceFace { .. }
             | K::Align { .. }
@@ -1410,6 +1424,7 @@ impl FeatureKind {
             FeatureKind::Scale { .. } => "ScaleFeature",
             FeatureKind::OffsetFace { .. } => "OffsetFacesFeature",
             FeatureKind::DeleteFace { .. } => "DeleteFaceFeature",
+            FeatureKind::SurfaceOffset { .. } => "OffsetSurfaceFeature",
             FeatureKind::BoundingSolid { .. } => "BoundingSolidFeature",
             FeatureKind::Pipe { .. } => "PipeFeature",
             FeatureKind::Emboss { .. } => "EmbossFeature",
@@ -1482,6 +1497,7 @@ impl FeatureKind {
             FeatureKind::Scale { .. } => "Scale",
             FeatureKind::OffsetFace { .. } => "OffsetFace",
             FeatureKind::DeleteFace { .. } => "DeleteFace",
+            FeatureKind::SurfaceOffset { .. } => "OffsetSurface",
             FeatureKind::BoundingSolid { .. } => "BoundingSolid",
             FeatureKind::Pipe { .. } => "Pipe",
             FeatureKind::Emboss { .. } => "Emboss",
@@ -1572,6 +1588,7 @@ impl FeatureKind {
             | FeatureKind::Draft { faces, .. }
             | FeatureKind::OffsetFace { faces, .. }
             | FeatureKind::DeleteFace { faces, .. }
+            | FeatureKind::SurfaceOffset { faces, .. }
             | FeatureKind::SplitFace { faces, .. }
             | FeatureKind::ReplaceFace { faces, .. } => faces.iter_mut().collect(),
             FeatureKind::Hole { position, points: None, to, .. } => std::iter::once(position).chain(to.iter_mut()).collect(),
@@ -1747,6 +1764,12 @@ impl FeatureKind {
             }
             FeatureKind::ReplaceFace { target, .. } => plane_exprs(target, &mut v),
             FeatureKind::Align { .. } | FeatureKind::Remove { .. } | FeatureKind::BoundaryFill { .. } | FeatureKind::DeleteFace { .. } => {}
+            FeatureKind::SurfaceOffset { distance, tolerance, .. } => {
+                v.push(distance);
+                if let Some(t) = tolerance {
+                    v.push(t);
+                }
+            }
             FeatureKind::Stitch { tolerance, .. } => v.push(tolerance),
             FeatureKind::MeshConvert { tolerance, .. } => v.push(tolerance),
             FeatureKind::Thicken { thickness, .. } => v.push(thickness),

crates/doc/src/eval.rs

@@ -3638,7 +3638,8 @@ fn eval_feature(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st:
         | FeatureKind::ReverseNormal { .. }
         | FeatureKind::SurfaceRevolve { .. }
         | FeatureKind::SurfaceSweep { .. }
-        | FeatureKind::SurfaceLoft { .. } => surface::eval(doc, vals, f, st),
+        | FeatureKind::SurfaceLoft { .. }
+        | FeatureKind::SurfaceOffset { .. } => surface::eval(doc, vals, f, st),
         FeatureKind::Emboss { .. }
         | FeatureKind::Rib { .. }
         | FeatureKind::ReplaceFace { .. }

crates/doc/src/eval_surface.rs

@@ -1,5 +1,6 @@
 //! Evaluation of the surface features: Patch, Stitch, Thicken, Trim, Extend, Surface Extrude,
-//! Revolve, Sweep and Loft, Unstitch and Reverse Normal (kernel `surfaces`).
+//! Revolve, Sweep and Loft, Offset, Unstitch and Reverse Normal (kernel `surfaces`,
+//! `surface_offset`).
 
 use super::*;
 use solidcraft_geom::Seg2;
@@ -211,6 +212,28 @@ pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature,
             push_sheet(st, f, traced);
             Ok(())
         }
+        FeatureKind::SurfaceOffset { faces, body, distance, chain, tolerance } => {
+            let d = val(vals, distance, Kind::Length)?;
+            let tol = match tolerance {
+                Some(t) => val(vals, t, Kind::Length)?,
+                None => 0.01,
+            };
+            let i = body_at(st, body, faces)?;
+            let Some(mb) = st.bodies.get(i).cloned() else { return Err(DocError::Invalid("body".into())) };
+            let picks = if *chain { smooth_chain(&mb, faces) } else { faces.clone() };
+            let mut picked: Vec<usize> = Vec::new();
+            for p in &picks {
+                let fi =
+                    crate::appearance::face_index_at(&mb, *p).ok_or_else(|| DocError::Invalid(format!("Offset: no face of {} at {p:?}", mb.name)))?;
+                if !picked.contains(&fi) {
+                    picked.push(fi);
+                }
+            }
+            let made = Traced::step(kernel::offset_surface(&mb.body, &picked, d, tol)?, &[&mb.traced()]);
+            let name = new_name(st, f, 0);
+            st.bodies.push(ModelBody::traced_new(name, made, f.id));
+            Ok(())
+        }
         _ => Err(DocError::Invalid("not a surface feature".into())),
     }
 }

crates/doc/src/format.rs

@@ -122,6 +122,8 @@
 //!   `path_sketch`, `path`) is also first saved in 18.
 //!   A `SurfaceLoft` feature (Surface Loft: `sections`, each a `sketch` with optional `profiles`
 //!   and `curves`) is also first saved in 18.
+//!   A `SurfaceOffset` feature (Offset Surface: `faces` points, optional `body`, `distance`,
+//!   `chain` and `tolerance`) is also first saved in 18.
 
 use serde_json::Value;
 

crates/doc/src/params.rs

@@ -278,6 +278,12 @@ impl FeatureKind {
             FeatureKind::SurfaceTrim { plane, .. } => plane_inputs_mut(plane, &mut v),
             FeatureKind::SurfaceExtend { distance, .. } => v.push(("Distance", distance, L)),
             FeatureKind::Unstitch { .. } | FeatureKind::ReverseNormal { .. } => {}
+            FeatureKind::SurfaceOffset { distance, tolerance, .. } => {
+                v.push(("Distance", distance, L));
+                if let Some(t) = tolerance {
+                    v.push(("Tolerance", t, L));
+                }
+            }
             FeatureKind::Patch { .. } => {}
             FeatureKind::Combine { .. }
             | FeatureKind::SheetBase { .. }

crates/engine/src/cmd/surface.rs

@@ -46,10 +46,10 @@ pub static COMMANDS: &[CommandSpec] = &[
         .at("SURFACE", "CREATE")
         .icon("surface_loft")
         .params("sections: [{sketch, curves?: [curve ids], profiles?}] (2…50 in order; each one chain: a profile without holes, or curves meeting end to end; all open or all closed); name?, body_name? (a surface body: ruled between two sections, smooth through three or more; no caps)"),
-    planned!("surface.offset", "Offset Surface", "758")
+    CommandSpec::new("surface.offset", "Offset Surface", offset)
         .at("SURFACE", "CREATE")
         .icon("surface_offset")
-        .params("planned: faces: [{body, point}]; distance: expr (signed, along the normals; 0 copies the faces); chain?: bool (the whole tangent chain of each pick); tolerance?: expr (B-spline fit, default 0.01 mm)"),
+        .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")
         .at("SURFACE", "CREATE")
         .icon("ruled")
@@ -186,6 +186,28 @@ fn surface_loft(s: &mut Session, p: &Value) -> Result<Value> {
     add_feature(s, p, FeatureKind::SurfaceLoft { sections })
 }
 
+fn offset(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "surface.offset";
+    let faces: Vec<solidcraft_geom::Vec3> = p.get("faces").and_then(Value::as_array).map(|a| a.iter().filter_map(vec3).collect()).unwrap_or_default();
+    if faces.is_empty() || faces.len() > 10_000 {
+        return Err(bad(cmd, "`faces` must list points on the faces to offset"));
+    }
+    let distance = expr(p, "distance").ok_or_else(|| bad(cmd, "`distance` is required"))?;
+    check_expr(s, &distance, Kind::Length, cmd, "distance")?;
+    let tolerance = expr(p, "tolerance");
+    if let Some(t) = &tolerance {
+        check_expr(s, t, Kind::Length, cmd, "tolerance")?;
+    }
+    let kind = FeatureKind::SurfaceOffset {
+        faces,
+        body: str_(p, "body").map(str::to_string),
+        distance,
+        chain: bool_(p, "chain").unwrap_or(false),
+        tolerance,
+    };
+    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() {
@@ -585,13 +607,43 @@ mod tests {
         }
     }
 
+    /// Offset Surface: a cylinder's side picked once with its chain (both halves) moved out to
+    /// radius 12; a box top moved up exactly; a zero distance copies; past the axis refused, the
+    /// design left as it was; undo, redo and reopening.
+    #[test]
+    fn offset_surface_of_a_cylinder_and_a_box_top() {
+        let mut s = Session::default();
+        run(&mut s, "solid.cylinder", json!({"radius": 10, "height": 20, "body_name": "Can"}));
+        run(&mut s, "surface.offset", json!({"faces": [[10, 0, 10]], "chain": true, "distance": 2, "body": "Can", "body_name": "Sleeve"}));
+        let st = s.world_state();
+        let sleeve = &st.body("Sleeve").unwrap().body;
+        assert!(sleeve.is_surface() && sleeve.face_count() == 2);
+        let want = 2.0 * std::f64::consts::PI * 12.0 * 20.0;
+        assert!((area(&s, "Sleeve") - want).abs() < want * 1e-3, "{} vs {want}", area(&s, "Sleeve")); // (measured on meshes)
+        assert!(st.body("Can").is_some(), "the source body stays");
+        run(&mut s, "solid.box", json!({"length": 10, "width": 10, "height": 10, "corner": [30, 0, 0], "body_name": "Box"}));
+        run(&mut s, "surface.offset", json!({"faces": [[35, 5, 10]], "distance": "5 mm", "body_name": "Lid"}));
+        let bb = solidcraft_kernel::measure(&s.world_state().body("Lid").unwrap().body).unwrap().bbox;
+        assert!((bb.min.z - 15.0).abs() < 1e-9 && (area(&s, "Lid") - 100.0).abs() < 1e-9);
+        run(&mut s, "surface.offset", json!({"faces": [[35, 5, 10]], "distance": 0, "body_name": "Copy"}));
+        assert!((area(&s, "Copy") - 100.0).abs() < 1e-9);
+        let before = s.doc.features.len();
+        assert!(s.execute("surface.offset", &json!({"faces": [[10, 0, 10]], "chain": true, "distance": -11, "body": "Can"})).is_err());
+        assert_eq!(s.doc.features.len(), before);
+        run(&mut s, "edit.undo", json!({}));
+        assert!(s.world_state().body("Copy").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, "Sleeve") - area(&s, "Sleeve")).abs() < 1e-9);
+        assert!(s.execute("surface.offset", &json!({"distance": 1})).is_err());
+    }
+
     /// The planned surface commands are registered but refuse to run: disabled with the
     /// issue that tracks them, an error (never a panic) from every caller, and the design left
     /// as it was.
     #[test]
     fn planned_commands_refuse_and_leave_the_design_alone() {
-        let planned =
-            ["surface.offset", "surface.ruled", "surface.boundary", "surface.blend", "surface.untrim", "surface.fillet", "inspect.continuity"];
+        let planned = ["surface.ruled", "surface.boundary", "surface.blend", "surface.untrim", "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

@@ -78,6 +78,7 @@ mod step;
 mod step_in;
 mod step_out;
 mod surface_kind;
+mod surface_offset;
 mod surfaces;
 mod sweep_path;
 mod tess;
@@ -116,6 +117,7 @@ pub use step::step_export;
 pub use step_in::{ImportedBody, StepImport, StepNode, step_import, step_import_shared, step_orientation_errors, step_validate};
 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 surfaces::{
     copy_faces, extend, extrude_sheet, loft_sheet, patch_edges, patch_region, remove_faces, reverse_faces, revolve_sheet, stitch, sweep_sheet,
     sweep_sheet_points, thicken, trim, unstitch,

crates/kernel/src/surface_offset.rs

@@ -0,0 +1,388 @@
+//! Offset surfaces (Surface › Offset): faces of a body copied out at a signed distance along
+//! their normals, as a new surface body. Planes and circular cylinders move exactly (as Thicken
+//! moves them); any other face gets a B-spline surface fitted through offset samples on a grid,
+//! refined until it is within a tolerance of the true offset everywhere it is checked. An
+//! offset as deep as a face's smallest concave radius would fold it over, and is refused,
+//! naming that radius. Neighbouring faces moved to the same place along their shared edge
+//! (meeting smoothly) keep sharing it; across a sharp edge they come apart. Faces that close up
+//! make a solid.
+
+use std::collections::HashMap;
+
+use mt::{BoundedCurve, InnerSpace, ParametricCurve, ParametricSurface, ParametricSurface3D, SearchNearestParameter};
+use solidcraft_geom::Vec3;
+use truck_modeling as mt;
+
+use crate::body::{Body, from_p3, p3};
+use crate::history::FaceOrigin;
+use crate::surfaces::{Offset, map_curve, map_surface, surface_body};
+use crate::{KernelError, Result, guard};
+
+/// Grid samples a side of a fitted offset starts with, and the most it is refined to.
+const START_GRID: usize = 12;
+const MAX_GRID: usize = 96;
+/// Samples along an edge of a fitted offset.
+const EDGE_SAMPLES: usize = 33;
+
+/// How one face moves.
+enum Moved {
+    Exact(Offset),
+    /// The fitted surface (absolute parameters of the face's own surface), and the face's
+    /// outward sign (its orientation).
+    Fitted {
+        surface: mt::BSplineSurface<mt::Point3>,
+        sign: f64,
+    },
+}
+
+/// The picked faces of `body` (indices in its face order) offset by `distance` along their
+/// outward normals (negative: against them) into one surface body. `tolerance`: how far a
+/// fitted face may stray from the true offset. A distance of zero copies the faces. The
+/// history is over `[body]`: each face is the offset of the one it came from.
+pub fn offset_surface(body: &Body, faces: &[usize], distance: f64, tolerance: f64) -> Result<Body> {
+    body.require_brep("offset")?;
+    if !(distance.is_finite() && distance.abs() < 1e6) {
+        return Err(KernelError::Invalid("the offset distance must be finite".into()));
+    }
+    if !(tolerance.is_finite() && (1e-6..=10.0).contains(&tolerance)) {
+        return Err(KernelError::Invalid("the offset tolerance must be 0.000001…10 mm".into()));
+    }
+    let all: Vec<mt::Face> = body.solid.face_iter().cloned().collect();
+    let mut picked: Vec<usize> = Vec::new();
+    for &i in faces {
+        if i >= all.len() {
+            return Err(KernelError::Invalid("no such face".into()));
+        }
+        if !picked.contains(&i) {
+            picked.push(i);
+        }
+    }
+    if picked.is_empty() {
+        return Err(KernelError::Invalid("pick the faces to offset".into()));
+    }
+    let chosen: Vec<(usize, &mt::Face)> = picked.iter().filter_map(|i| all.get(*i).map(|f| (*i, f))).collect();
+    if distance == 0.0 {
+        let copy = surface_body(chosen.iter().map(|(_, f)| (*f).clone()).collect());
+        return Ok(crate::record::rebuilt_body(copy, &[&body.solid], &crate::record::Rebuild::default()));
+    }
+    let size = body.size().max(1e-6);
+    let moves: Vec<Moved> = chosen
+        .iter()
+        .map(|(_, f)| match Offset::of(f) {
+            Some(off) => {
+                if let Offset::Cylinder { r, out, .. } = off
+                    && r + out * distance <= tolerance
+                {
+                    return Err(KernelError::Invalid(format!(
+                        "the offset is as deep as the cylinder's radius ({r:.4} mm): it would fold the face over"
+                    )));
+                }
+                Ok(Moved::Exact(off))
+            }
+            None => fit(f, distance, tolerance),
+        })
+        .collect::<Result<_>>()?;
+    guard("offset surface", || {
+        let near = |a: Vec3, b: Vec3| a.dist(b) <= tolerance.max(size * 1e-7) * 4.0;
+        // Moved vertices and edges, shared while every face moves them to the same place.
+        let mut verts: HashMap<mt::VertexID, Vec<mt::Vertex>> = HashMap::new();
+        let mut edges: HashMap<mt::EdgeID, Vec<mt::Edge>> = HashMap::new();
+        let mut out = Vec::with_capacity(chosen.len());
+        let mut history = Vec::with_capacity(chosen.len());
+        for ((i, f), mv) in chosen.iter().zip(&moves) {
+            let map = |p: Vec3| -> Result<Vec3> {
+                match mv {
+                    Moved::Exact(off) => Ok(off.map(p, distance)),
+                    Moved::Fitted { sign, .. } => offset_point(&f.surface(), p, *sign * distance),
+                }
+            };
+            let mut vertex = |v: &mt::Vertex| -> Result<mt::Vertex> {
+                let at = map(from_p3(v.point()))?;
+                let list = verts.entry(v.id()).or_default();
+                if let Some(found) = list.iter().find(|m| near(from_p3(m.point()), at)) {
+                    return Ok(found.clone());
+                }
+                let nv = mt::Vertex::new(p3(at));
+                list.push(nv.clone());
+                Ok(nv)
+            };
+            let mut wires = Vec::new();
+            for w in f.absolute_boundaries() {
+                let mut wire = Vec::new();
+                for e in w.edge_iter() {
+                    let abs = if e.orientation() { e.clone() } else { e.inverse() };
+                    let (a, b) = (vertex(abs.front())?, vertex(abs.back())?);
+                    let c = abs.curve();
+                    let (t0, t1) = c.range_tuple();
+                    let mid = map(from_p3(c.subs(0.5 * (t0 + t1))))?;
+                    let list = edges.entry(abs.id()).or_default();
+                    let shared = list.iter().find(|m| {
+                        m.front().id() == a.id() && m.back().id() == b.id() && {
+                            let mc = m.curve();
+                            let (s0, s1) = mc.range_tuple();
+                            near(from_p3(mc.subs(0.5 * (s0 + s1))), mid)
+                        }
+                    });
+                    let moved = match shared {
+                        Some(m) => m.clone(),
+                        None => {
+                            let curve = match mv {
+                                Moved::Exact(off) => map_curve(off, &c, distance)?,
+                                Moved::Fitted { .. } => {
+                                    let pts: Vec<Vec3> = (0..EDGE_SAMPLES)
+                                        .map(|k| map(from_p3(c.subs(t0 + (t1 - t0) * k as f64 / (EDGE_SAMPLES - 1) as f64))))
+                                        .collect::<Result<_>>()?;
+                                    mt::Curve::BSplineCurve(
+                                        crate::build::interpolate_cubic(&pts).ok_or_else(|| KernelError::Failed("offset edge".into()))?,
+                                    )
+                                }
+                            };
+                            let m = mt::Edge::new_unchecked(&a, &b, curve);
+                            list.push(m.clone());
+                            m
+                        }
+                    };
+                    wire.push(if e.orientation() { moved } else { moved.inverse() });
+                }
+                wires.push(mt::Wire::from(wire));
+            }
+            let surface = match mv {
+                Moved::Exact(off) => map_surface(off, &f.surface(), distance)?,
+                Moved::Fitted { surface, .. } => mt::Surface::BSplineSurface(surface.clone()),
+            };
+            let mut nf = mt::Face::new_unchecked(wires, surface);
+            if !f.orientation() {
+                nf.invert();
+            }
+            out.push(nf);
+            history.push(crate::record::generated(vec![FaceOrigin::Offset { operand: 0, face: *i }]));
+        }
+        let operand = crate::record::Operand::new(body);
+        // Faces that close up (every face of a smooth closed body) make a solid, as Stitch makes
+        // one.
+        let shell = mt::Shell::from(out);
+        let result = match shell.shell_condition() {
+            mt::ShellCondition::Closed => match crate::body::Solid::try_new(vec![shell.clone()]) {
+                Ok(solid) => Body::new(solid)?,
+                Err(_) => surface_body(shell.into_iter().collect()),
+            },
+            _ => surface_body(shell.into_iter().collect()),
+        };
+        crate::record::attach(result, &[operand], Some(history), HashMap::new())
+    })
+}
+
+/// The point `p` on `s` (absolute) moved by `d` along the surface's own normal there.
+fn offset_point(s: &mt::Surface, p: Vec3, d: f64) -> Result<Vec3> {
+    let (u, v) = s.search_nearest_parameter(p3(p), None, 100).ok_or_else(|| KernelError::Failed("offset: a point off its face".into()))?;
+    let n = from_p3(mt::Point3::new(0.0, 0.0, 0.0) + s.normal(u, v));
+    let n =
+        n.normalized().ok_or_else(|| KernelError::Invalid("the face has a point with no normal (a pole or a crease): not supported yet".into()))?;
+    Ok(from_p3(s.subs(u, v)) + n * d)
+}
+
+/// The fitted offset of a face that is not a plane or a circular cylinder.
+fn fit(f: &mt::Face, distance: f64, tolerance: f64) -> Result<Moved> {
+    let s = f.surface();
+    let sign = if f.orientation() { 1.0 } else { -1.0 };
+    let d = sign * distance;
+    // The face's span in its surface's parameters: its boundary, found on the surface.
+    let (mut u0, mut u1, mut v0, mut v1) = (f64::INFINITY, f64::NEG_INFINITY, f64::INFINITY, f64::NEG_INFINITY);
+    for e in f.absolute_boundaries().iter().flat_map(|w| w.edge_iter()) {
+        let c = e.curve();
+        let (t0, t1) = c.range_tuple();
+        for k in 0..=16 {
+            let q = c.subs(t0 + (t1 - t0) * k as f64 / 16.0);
+            if let Some((u, v)) = s.search_nearest_parameter(q, None, 100) {
+                (u0, u1, v0, v1) = (u0.min(u), u1.max(u), v0.min(v), v1.max(v));
+            }
+        }
+    }
+    if !(u0.is_finite() && u1 > u0 && v0.is_finite() && v1 > v0) {
+        return Err(KernelError::Failed("offset: the face's span on its surface".into()));
+    }
+    let at = |a: f64, b: f64| -> Result<Vec3> {
+        let (u, v) = (u0 + (u1 - u0) * a, v0 + (v1 - v0) * b);
+        let n = from_p3(mt::Point3::new(0.0, 0.0, 0.0) + s.normal(u, v));
+        let n = n
+            .normalized()
+            .ok_or_else(|| KernelError::Invalid("the face has a point with no normal (a pole or a crease): not supported yet".into()))?;
+        Ok(from_p3(s.subs(u, v)) + n * d)
+    };
+    // Folding over: moving a point by d along its normal shrinks lengths along a principal
+    // direction by 1 - d·k (k > 0 where the surface bends toward its normal); at zero the
+    // offset reaches the centre of curvature and folds. Refused with a margin, naming the
+    // tightest radius on that side.
+    let mut tightest: Option<f64> = None;
+    for i in 0..=START_GRID {
+        for j in 0..=START_GRID {
+            let (u, v) = (u0 + (u1 - u0) * i as f64 / START_GRID as f64, v0 + (v1 - v0) * j as f64 / START_GRID as f64);
+            let Some((k1, k2)) = principal_curvatures(&s, u, v) else { continue };
+            for k in [k1, k2] {
+                if d * k > 0.0 && 1.0 - d * k <= 0.05 {
+                    let r = 1.0 / k.abs();
+                    tightest = Some(tightest.map_or(r, |t: f64| t.min(r)));
+                }
+            }
+        }
+    }
+    if let Some(r) = tightest {
+        return Err(KernelError::Invalid(format!(
+            "the offset is as deep as the face's smallest concave radius on that side ({r:.4} mm): it would fold the face over"
+        )));
+    }
+    let mut n = START_GRID;
+    loop {
+        let grid: Vec<Vec<Vec3>> =
+            (0..=n).map(|i| (0..=n).map(|j| at(i as f64 / n as f64, j as f64 / n as f64)).collect::<Result<Vec<_>>>()).collect::<Result<_>>()?;
+        let surface = interpolate_surface(&grid).ok_or_else(|| KernelError::Failed("offset: fitting the surface".into()))?;
+        // Checked between the samples, where a fit strays most.
+        let mut worst = 0.0f64;
+        for i in 0..n {
+            for j in 0..n {
+                let (a, b) = ((i as f64 + 0.5) / n as f64, (j as f64 + 0.5) / n as f64);
+                worst = worst.max(from_p3(surface.subs(a, b)).dist(at(a, b)?));
+            }
+        }
+        if worst <= tolerance {
+            // Re-parameterised to the face's own surface span, so boundary points found on the
+            // old surface map onto it.
+            return Ok(Moved::Fitted { surface: reparameterised(surface, (u0, u1), (v0, v1)), sign });
+        }
+        if n >= MAX_GRID {
+            return Err(KernelError::Invalid(format!(
+                "the offset can't be fitted within {tolerance} mm (off by up to {worst:.4} mm): try a larger tolerance"
+            )));
+        }
+        n = (n * 2).min(MAX_GRID);
+    }
+}
+
+/// The principal curvatures of `s` at (u, v), signed: positive where the surface bends toward
+/// its normal there. `None` where it has no normal.
+fn principal_curvatures(s: &mt::Surface, u: f64, v: f64) -> Option<(f64, f64)> {
+    let (su, sv) = (s.uder(u, v), s.vder(u, v));
+    let n = s.normal(u, v);
+    if !(n.magnitude2() > 0.5) {
+        return None;
+    }
+    let (e, f, g) = (su.dot(su), su.dot(sv), sv.dot(sv));
+    let (l, m, nn) = (s.uuder(u, v).dot(n), s.uvder(u, v).dot(n), s.vvder(u, v).dot(n));
+    let det = e * g - f * f;
+    if det.abs() < 1e-18 {
+        return None;
+    }
+    let k = (l * nn - m * m) / det;
+    let h = (e * nn - 2.0 * f * m + g * l) / (2.0 * det);
+    let disc = (h * h - k).max(0.0).sqrt();
+    Some((h + disc, h - disc))
+}
+
+/// A cubic B-spline surface through a grid of points at uniform parameters on [0, 1]².
+fn interpolate_surface(grid: &[Vec<Vec3>]) -> Option<mt::BSplineSurface<mt::Point3>> {
+    let rows: Vec<mt::BSplineCurve<mt::Point3>> = grid.iter().map(|r| crate::build::interpolate_cubic(r)).collect::<Option<_>>()?;
+    let kv = rows.first()?.knot_vec().clone();
+    let m = rows.first()?.control_points().len();
+    let mut cols = Vec::with_capacity(m);
+    for j in 0..m {
+        let pts: Vec<Vec3> = rows.iter().filter_map(|r| r.control_points().get(j).map(|p| from_p3(*p))).collect();
+        cols.push(crate::build::interpolate_cubic(&pts)?);
+    }
+    let ku = cols.first()?.knot_vec().clone();
+    let n = cols.first()?.control_points().len();
+    let net: Vec<Vec<mt::Point3>> = (0..n).map(|i| cols.iter().filter_map(|c| c.control_points().get(i).copied()).collect()).collect();
+    mt::BSplineSurface::try_new((ku, kv), net).ok()
+}
+
+/// `s` (on [0, 1]²) with its knots stretched onto `u` × `v`.
+fn reparameterised(s: mt::BSplineSurface<mt::Point3>, u: (f64, f64), v: (f64, f64)) -> mt::BSplineSurface<mt::Point3> {
+    let stretch = |kv: &mt::KnotVec, (a, b): (f64, f64)| mt::KnotVec::from(kv.iter().map(|k| a + (b - a) * k).collect::<Vec<_>>());
+    let (ku, kv) = (stretch(s.uknot_vec(), u), stretch(s.vknot_vec(), v));
+    mt::BSplineSurface::new((ku, kv), s.control_points().clone())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{box_solid, cylinder, measure, sphere};
+
+    fn rel(a: f64, b: f64) -> f64 {
+        (a - b).abs() / b.abs().max(1e-9)
+    }
+    fn face_at(b: &Body, p: Vec3) -> usize {
+        crate::surfaces::nearest_face(b, p).unwrap()
+    }
+    fn edges(b: &Body) -> usize {
+        b.solid.edge_iter().map(|e| e.id()).collect::<std::collections::HashSet<_>>().len()
+    }
+
+    /// Planes move exactly: a box's top 5 up is a 10 × 10 square at z = 15. Two faces across a
+    /// sharp edge come apart (8 edges, none shared); a zero distance copies.
+    #[test]
+    fn planes_move_and_sharp_edges_come_apart() {
+        let b = box_solid(Vec3::ZERO, Vec3::new(10.0, 10.0, 10.0)).unwrap();
+        let top = face_at(&b, Vec3::new(5.0, 5.0, 10.0));
+        let up = offset_surface(&b, &[top], 5.0, 0.01).unwrap();
+        let m = measure(&up).unwrap();
+        assert!(up.is_surface() && rel(m.area, 100.0) < 1e-9 && (m.bbox.min.z - 15.0).abs() < 1e-9, "{m:?}");
+        let side = face_at(&b, Vec3::new(5.0, 0.0, 5.0));
+        let two = offset_surface(&b, &[top, side], 1.0, 0.01).unwrap();
+        assert!(two.face_count() == 2 && edges(&two) == 8);
+        let copy = offset_surface(&b, &[top, side], 0.0, 0.01).unwrap();
+        assert!(copy.face_count() == 2 && rel(measure(&copy).unwrap().area, 200.0) < 1e-9);
+    }
+
+    /// A cylinder's side (two halves) moved out by 2 keeps its halves joined, with radius 12:
+    /// area 2π·12·20. Moved in past its axis, refused.
+    #[test]
+    fn a_cylinder_side_changes_radius() {
+        let c = cylinder(Vec3::ZERO, Vec3::Z, 10.0, 20.0).unwrap();
+        let d = 10.0 / 2f64.sqrt();
+        let halves = [face_at(&c, Vec3::new(d, d, 10.0)), face_at(&c, Vec3::new(-d, -d, 10.0))];
+        let out = offset_surface(&c, &halves, 2.0, 0.01).unwrap();
+        assert!(out.face_count() == 2);
+        let want = 2.0 * std::f64::consts::PI * 12.0 * 20.0;
+        assert!(rel(measure(&out).unwrap().area, want) < 1e-3, "{} vs {want}", measure(&out).unwrap().area); // (measured on meshes)
+        let joined = offset_surface(&c, &halves, 0.0, 0.01).unwrap();
+        assert_eq!(edges(&out), edges(&joined), "the halves still share their seams");
+        assert!(offset_surface(&c, &halves, -10.5, 0.01).is_err());
+    }
+
+    /// A sphere (fitted faces) moved out by 2: area 4π·12², within the tolerance; moved in to
+    /// its centre, refused with its radius named.
+    #[test]
+    fn a_sphere_is_fitted_and_refused_past_its_centre() {
+        let s = sphere(Vec3::ZERO, 10.0).unwrap();
+        let all: Vec<usize> = (0..s.face_count()).collect();
+        let out = offset_surface(&s, &all, 2.0, 0.01).unwrap();
+        let want = 4.0 * std::f64::consts::PI * 144.0;
+        assert!(rel(measure(&out).unwrap().area, want) < 2e-3, "{} vs {want}", measure(&out).unwrap().area); // (measured on meshes)
+        // The patches meet smoothly: their offsets still share every edge, and close up.
+        assert_eq!(edges(&out), edges(&s));
+        assert!(!out.is_surface(), "the offset sphere closes into a solid");
+        assert!(rel(measure(&out).unwrap().volume, 4.0 / 3.0 * std::f64::consts::PI * 1728.0) < 2e-3, "outward"); // (measured on meshes)
+        let e = offset_surface(&s, &all, -10.0, 0.01).unwrap_err().to_string();
+        assert!(e.contains("10.0000"), "{e}");
+    }
+
+    /// A doubly curved patch (a saddle, a B-spline height field) moved by 1.5: every point of the
+    /// offset lies 1.5 from the patch, within the tolerance.
+    #[test]
+    fn a_bspline_patch_is_offset_within_the_tolerance() {
+        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 face = cover.solid.face_iter().next().unwrap().clone();
+        let out = offset_surface(&cover, &[0], 1.5, 0.01).unwrap();
+        let mesh = out.tessellate(0.05).unwrap();
+        let s = face.surface();
+        for p in mesh.positions.iter().step_by(7) {
+            let (u, v) = s.search_nearest_parameter(p3(*p), None, 100).unwrap();
+            let dist = from_p3(s.subs(u, v)).dist(*p);
+            assert!((dist - 1.5).abs() < 0.03, "{dist} at {p:?}");
+        }
+    }
+}

crates/kernel/src/surfaces.rs

@@ -536,7 +536,7 @@ pub fn remove_faces(body: &Body, faces: &[usize]) -> Result<Body> {
 }
 
 /// Index of the face nearest a point (over its mesh triangles).
-fn nearest_face(body: &Body, p: Vec3) -> Result<usize> {
+pub(crate) fn nearest_face(body: &Body, p: Vec3) -> Result<usize> {
     let m = body.tessellate(body.size() * 2e-3)?;
     let mut best: Option<(f64, u32)> = None;
     for (t, f) in m.triangles.iter().zip(&m.tri_face) {
@@ -662,19 +662,19 @@ pub fn stitch(bodies: &[&Body], tol: f64) -> Result<Body> {
 
 /// How a face moves along its normal: a plane slides, a circular cylinder changes radius.
 #[derive(Clone, Copy)]
-enum Offset {
+pub(crate) enum Offset {
     Plane { n: Vec3 },
     Cylinder { o: Vec3, axis: Vec3, r: f64, out: f64 },
 }
 
 impl Offset {
-    fn of(f: &mt::Face) -> Option<Offset> {
+    pub(crate) fn of(f: &mt::Face) -> Option<Offset> {
         match crate::splitface::analytic_field(&f.oriented_surface())? {
             crate::splitface::Analytic::Plane { n } => Some(Offset::Plane { n }),
             crate::splitface::Analytic::Cylinder { o, axis, r, out } => Some(Offset::Cylinder { o, axis, r, out }),
         }
     }
-    fn map(&self, p: Vec3, d: f64) -> Vec3 {
+    pub(crate) fn map(&self, p: Vec3, d: f64) -> Vec3 {
         match *self {
             Offset::Plane { n } => p + n * d,
             // Scaled about the axis (control points of a NURBS circle stay exact).
@@ -693,7 +693,7 @@ 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).
-fn map_curve(off: &Offset, c: &mt::Curve, d: f64) -> Result<mt::Curve> {
+pub(crate) fn map_curve(off: &Offset, c: &mt::Curve, d: f64) -> Result<mt::Curve> {
     Ok(match c {
         mt::Curve::Line(l) => mt::Curve::Line(mt::Line(map_pt(off, l.0, d), map_pt(off, l.1, d))),
         mt::Curve::BSplineCurve(b) => {
@@ -723,7 +723,7 @@ fn map_curve(off: &Offset, c: &mt::Curve, d: f64) -> Result<mt::Curve> {
 }
 
 /// A surface moved by an offset (control points mapped; exact for planes and NURBS cylinders).
-fn map_surface(off: &Offset, s: &mt::Surface, d: f64) -> Result<mt::Surface> {
+pub(crate) fn map_surface(off: &Offset, s: &mt::Surface, d: f64) -> Result<mt::Surface> {
     Ok(match s {
         mt::Surface::Plane(pl) => {
             let (o, a, b) = (pl.origin(), pl.u_axis(), pl.v_axis());

crates/ui-egui/src/dialogs_surface.rs

@@ -30,6 +30,10 @@ pub enum Surf {
     Patch,
     Unstitch,
     ReverseNormal,
+    Offset {
+        distance: String,
+        chain: bool,
+    },
     Stitch {
         tolerance: String,
     },
@@ -58,6 +62,7 @@ impl Surf {
             Surf::Patch => "PATCH",
             Surf::Unstitch => "UNSTITCH",
             Surf::ReverseNormal => "REVERSE NORMAL",
+            Surf::Offset { .. } => "OFFSET SURFACE",
             Surf::Stitch { .. } => "STITCH",
             Surf::ConvertMesh { .. } => "CONVERT MESH",
             Surf::Thicken { .. } => "THICKEN",
@@ -71,7 +76,7 @@ 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, .. } => ("Distance", ValueKind::Length, distance),
+            Surf::Extend { distance } | Surf::Extrude { distance, .. } | Surf::Offset { distance, .. } => ("Distance", ValueKind::Length, distance),
             Surf::Revolve { angle, .. } => ("Angle", ValueKind::Angle, angle),
             _ => return None,
         })
@@ -90,6 +95,7 @@ fn inputs(k: &Surf) -> Vec<SelInput> {
         Surf::Patch => vec![SelInput::new("Boundary", PROFILES | EDGES, true)],
         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::Stitch { .. } => vec![SelInput::new("Surfaces", BODIES, true)],
         Surf::ConvertMesh { .. } => vec![SelInput::new("Mesh body", BODIES, false)],
         Surf::Thicken { .. } => vec![SelInput::new("Surfaces", BODIES, true)],
@@ -113,6 +119,7 @@ pub fn start(_app: &SolveApp, id: &str) -> Option<(Kind, Vec<SelInput>)> {
         "surface.patch" => Surf::Patch,
         "surface.unstitch" => Surf::Unstitch,
         "surface.reverse_normal" => Surf::ReverseNormal,
+        "surface.offset" => Surf::Offset { distance: "2 mm".into(), chain: 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 },
@@ -164,6 +171,14 @@ pub fn rows(ui: &mut egui::Ui, k: &mut Surf) -> bool {
             *symmetric = dir == 1;
             ui.end_row();
         }
+        Surf::Offset { distance, chain } => {
+            row_label(ui, "Distance");
+            enter |= field(ui, distance);
+            ui.end_row();
+            row_label(ui, "Tangent chain");
+            ui.checkbox(chain, "");
+            ui.end_row();
+        }
         Surf::Extrude { distance, direction } => {
             row_label(ui, "Distance");
             enter |= field(ui, distance);
@@ -327,6 +342,18 @@ pub fn commands(app: &SolveApp, k: &Surf, inputs: &[SelInput], extra: &Map<Strin
                 ("surface.patch", json!({"edges": edges, "body": body}))
             }
         }
+        Surf::Offset { distance, chain } => {
+            need(0, "the faces to offset")?;
+            let (body, faces) = body_and_faces(items(inputs, 0))?;
+            if faces.is_empty() {
+                return Err("pick faces to offset".into());
+            }
+            let mut p = json!({"body": body, "faces": faces, "distance": distance});
+            if *chain {
+                p["chain"] = json!(true);
+            }
+            ("surface.offset", p)
+        }
         Surf::Unstitch | Surf::ReverseNormal => {
             need(0, "a body or some of its faces")?;
             let (body, faces) = body_and_faces(items(inputs, 0))?;
@@ -459,6 +486,9 @@ pub fn for_feature(app: &SolveApp, kind: &FeatureKind, frame: &Mat) -> Option<(K
             }
             (Surf::Patch, vec![sels])
         }
+        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::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

@@ -939,6 +939,31 @@ 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 offset_surface_dialog_takes_faces_a_distance_and_the_chain() {
+    // A box top picked, moved up 5: a 10 × 10 square at z = 15; Edit Feature brings it back.
+    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.offset");
+    assert!(apply_commands(&app, &d).is_err(), "no faces yet");
+    d.inputs[0].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::Offset { distance, chain }) = &mut d.kind {
+        *distance = "5 mm".into();
+        *chain = true;
+    }
+    let (id, p) = apply_commands(&app, &d).unwrap().remove(0);
+    assert_eq!(
+        (id.as_str(), &p["body"], &p["faces"], &p["chain"]),
+        ("surface.offset", &json!("Box"), &json!([[5.0, 5.0, 10.0]]), &json!(true)),
+        "{p}"
+    );
+    app.session.execute(&id, &p).unwrap();
+    let m = app.session.model.state().bodies.last().unwrap().mesh().measure();
+    assert!((m.area - 100.0).abs() < 1e-6, "{}", m.area);
+    let fid = app.session.doc.features.last().unwrap().id;
+    let back = crate::dialogs::for_feature(&app, fid, None).unwrap();
+    assert_eq!(back.inputs[0].items.len(), 1);
+}
+
 #[test]
 fn patch_dialog_fills_a_loop_of_edges_that_is_not_planar() {
     // A box with its top cut away by a sideways cylinder: its rim is a closed loop of four

crates/ui-egui/src/timeline.rs

@@ -17,6 +17,7 @@ pub(crate) fn icon_of(k: &FeatureKind) -> &'static str {
         FeatureKind::SurfaceRevolve { .. } => "surface_revolve",
         FeatureKind::SurfaceSweep { .. } => "surface_sweep",
         FeatureKind::SurfaceLoft { .. } => "surface_loft",
+        FeatureKind::SurfaceOffset { .. } => "surface_offset",
         FeatureKind::Revolve { .. } => "revolve",
         FeatureKind::Fillet { .. } => "fillet",
         FeatureKind::Chamfer { .. } => "chamfer",

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`). **341 commands.** Planned (registered, not built yet): 7. 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`). **342 commands.** Planned (registered, not built yet): 6. 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 (98)
 
@@ -145,7 +145,7 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 | Align | `solid.align` | SOLID › MODIFY |
 | Remove | `solid.remove` | SOLID › MODIFY |
 
-## Surfaces (11, 6 planned)
+## Surfaces (12, 5 planned)
 
 | Command | Id | Toolbar |
 |---|---|---|
@@ -158,7 +158,7 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 | Surface Revolve | `surface.revolve` | SURFACE › CREATE |
 | Surface Sweep | `surface.sweep` | SURFACE › CREATE |
 | Surface Loft | `surface.loft` | SURFACE › CREATE |
-| Offset Surface *(planned: [#758](https://github.com/bherbruck/solidcraft/issues/758))* | `surface.offset` | SURFACE › CREATE |
+| Offset Surface | `surface.offset` | SURFACE › CREATE |
 | Ruled Surface *(planned: [#762](https://github.com/bherbruck/solidcraft/issues/762))* | `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 |