Sketch Offset on two sides, or symmetric about the source (#807)

Sketch Offset can place the copy on both sides of the source, or symmetric about it.

crates/engine/src/cmd/sketch_modify.rs

@@ -42,7 +42,12 @@ pub static COMMANDS: &[CommandSpec] = &[
         .icon("offset")
         .key("O")
         .enabled(in_sketch)
-        .params(concat!("curves: [ids], distance: number (positive = left of the chain, or toward `side`), side?: [x,y], chain?: bool (default true: the connected chain)", created_doc!())),
+        .params(concat!(
+            "curves: [ids], distance: number (positive = left of the chain, or toward `side`), side?: [x,y], chain?: bool (default true: the connected chain); ",
+            "direction?: one_side|symmetric (default one_side) or symmetric?: bool (the same distance each way, as for `solid.extrude`; no `side`, whose job it takes over), ",
+            "distance2?: positive number (Two Sides: an independent distance the other way, as for `solid.extrude`). Each side is its own offset association, listed in `sides`",
+            created_doc!()
+        )),
     CommandSpec::new("sketch.offset.break", "Break Offset Association", break_offset)
         .enabled(in_sketch)
         .params("curve: derived offset curve id (retains geometry and makes its points editable)"),
@@ -919,6 +924,148 @@ fn piece_dist(p: &Piece, q: Vec2) -> f64 {
     }
 }
 
+/// One side of an offset. The curves created at the signed distance, the parallel constraints
+/// added with them, and the association when the boundary carries an offset topology.
+struct Side {
+    distance: f64,
+    curves: Vec<String>,
+    constraints: Vec<String>,
+    association: Option<String>,
+}
+
+/// The signed distances an offset runs at. One side is the distance as given. `symmetric` is the
+/// same distance each way, as `direction: symmetric` means for `solid.extrude`. `distance2` is an
+/// independent distance the other way, as `distance2` means for `solid.extrude`. The primary side
+/// comes first, so a one-sided caller reads the same first entry it always did.
+fn offset_runs(d: f64, symmetric: bool, distance2: Option<f64>) -> Vec<f64> {
+    match (symmetric, distance2) {
+        (true, _) => vec![d.abs(), -d.abs()],
+        (_, Some(second)) => vec![d, -second * d.signum()],
+        _ => vec![d],
+    }
+}
+
+/// Build one side of a chain offset at the signed distance `d`. `order` and `sources` are the
+/// walked chain, computed once before anything is created so a second side walks the same
+/// curves rather than a pool the first side has already grown.
+fn offset_side(sk: &mut Sketch, cmd: &str, order: &[(usize, bool)], sources: &[(String, bool)], closed: bool, convex: bool, d: f64) -> Result<Side> {
+    let mut made = Vec::new();
+    let mut cons = Vec::new();
+    if convex {
+        let created = sk.add_convex_offset(sources.to_vec(), d)?;
+        let roles = sk
+            .offsets
+            .iter()
+            .filter_map(|offset| offset.topology.as_ref())
+            .find(|topology| topology.id == created.association)
+            .map(|topology| topology.roles.clone())
+            .ok_or_else(|| bad(cmd, "new offset association is missing"))?;
+        for (source, role) in sources.iter().zip(&roles) {
+            if role.kind == solidcraft_sketch::OffsetRoleKind::Line {
+                let a = sk.curve_index(&source.0).ok_or_else(|| bad(cmd, "offset source line vanished"))?;
+                let b = sk.curve_index(&role.output).ok_or_else(|| bad(cmd, "offset output line vanished"))?;
+                cons.push(add_c(sk, ConstraintKind::Parallel { a, b })?);
+            }
+        }
+        return Ok(Side { distance: d, curves: created.curves, constraints: cons, association: Some(created.association) });
+    }
+    let pieces: Vec<Piece> =
+        order.iter().map(|(c, f)| offset_piece(sk, *c, *f, d)).collect::<Option<_>>().ok_or_else(|| bad(cmd, "the offset collapses an arc"))?;
+    let n = pieces.len();
+    let start_of = |p: &Piece| match p {
+        Piece::Line(a, _) => *a,
+        Piece::Arc(_, _, _, s, _, _) => *s,
+        Piece::Free(v) => v.first().copied().unwrap_or_default(),
+    };
+    let end_of = |p: &Piece| match p {
+        Piece::Line(_, b) => *b,
+        Piece::Arc(_, _, _, _, e, _) => *e,
+        Piece::Free(v) => v.last().copied().unwrap_or_default(),
+    };
+    // Junction points between consecutive pieces.
+    let joint = |x: &Piece, y: &Piece| -> Vec2 {
+        let (e, s0) = (end_of(x), start_of(y));
+        if e.dist(s0) < TOL * 10.0 {
+            return e;
+        }
+        let guess = (e + s0) * 0.5;
+        if matches!(x, Piece::Free(_)) || matches!(y, Piece::Free(_)) {
+            return guess;
+        }
+        intersections(&piece_shape(x), &piece_shape(y)).into_iter().min_by(|a, b| a.dist(guess).total_cmp(&b.dist(guess))).unwrap_or(guess)
+    };
+    let (Some(head), Some(tail)) = (pieces.first(), pieces.last()) else {
+        return Err(bad(cmd, "no curves"));
+    };
+    let mut joints: Vec<Vec2> = Vec::new();
+    joints.push(if closed { joint(tail, head) } else { start_of(head) });
+    for k in 0..n.saturating_sub(1) {
+        let (Some(x), Some(y)) = (pieces.get(k), pieces.get(k + 1)) else {
+            return Err(bad(cmd, "the offset chain changed while it was built"));
+        };
+        joints.push(joint(x, y));
+    }
+    if !closed {
+        joints.push(end_of(tail));
+    }
+    // A straight piece whose joints come out reversed (or meet) was overrun by its
+    // neighbours: the offset is larger than the shape allows there.
+    for (k, pc) in pieces.iter().enumerate() {
+        if let Piece::Line(a, b) = pc {
+            let (ja, jb) = (joints.get(k).copied(), joints.get(if closed { (k + 1) % n } else { k + 1 }).copied());
+            if let (Some(ja), Some(jb)) = (ja, jb)
+                && (jb - ja).dot(*b - *a) <= TOL * a.dist(*b)
+            {
+                return Err(bad(cmd, "the offset is larger than the shape allows (the offset curves would cross)"));
+            }
+        }
+    }
+    let pts: Vec<usize> = joints.iter().map(|q| sk.add_point(*q, None)).collect::<std::result::Result<_, _>>()?;
+    for (k, pc) in pieces.iter().enumerate() {
+        let (Some(pa), Some(pb)) = (pts.get(k).copied(), pts.get(if closed { (k + 1) % n } else { k + 1 }).copied()) else {
+            return Err(bad(cmd, "the offset chain changed while it was built"));
+        };
+        let orig = order.get(k).map(|(c, _)| *c).ok_or_else(|| bad(cmd, "the offset chain changed while it was built"))?;
+        match pc.clone() {
+            Piece::Free(v) => {
+                // A fit spline through a few of the samples, ending at the joints.
+                let step = (v.len() / 24).max(1);
+                let mut idx = vec![pa];
+                for q in v.iter().skip(step).step_by(step) {
+                    if q.dist(*v.last().unwrap_or(q)) > 1e-6 {
+                        idx.push(sk.add_point(*q, None)?);
+                    }
+                }
+                idx.push(pb);
+                idx.dedup();
+                if idx.len() >= 2 {
+                    made.push(sk.add_curve(CurveKind::Spline { pts: idx, control: false, degree: 3, periodic: false }, None)?);
+                }
+            }
+            Piece::Line(..) => {
+                let l = sk.add_line_pts(pa, pb, None)?;
+                cons.push(add_c(sk, ConstraintKind::Parallel { a: orig, b: l })?);
+                made.push(l);
+            }
+            Piece::Arc(ci, cc, _, _, _, ccw) => {
+                let (qa, qb) = (sk.point(pa).unwrap_or_default(), sk.point(pb).unwrap_or_default());
+                let a = if ccw {
+                    sk.add_arc(cc, qa, qb, [Some(ci), Some(pa), Some(pb)], None)?
+                } else {
+                    sk.add_arc(cc, qb, qa, [Some(ci), Some(pb), Some(pa)], None)?
+                };
+                made.push(a);
+            }
+        }
+    }
+    let outputs = ids_of(sk, &made);
+    if pieces.iter().all(|p| !matches!(p, Piece::Free(_))) {
+        sk.offsets.push(solidcraft_sketch::OffsetChain { sources: sources.to_vec(), outputs: outputs.clone(), distance: d, closed, topology: None });
+        sk.refresh_offsets()?;
+    }
+    Ok(Side { distance: d, curves: outputs, constraints: cons, association: None })
+}
+
 fn offset(s: &mut Session, p: &Value) -> Result<Value> {
     let cmd = "sketch.offset";
     let ids = string_list(p, "curves");
@@ -928,7 +1075,32 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
     let d0 = num(p, "distance").filter(|d| d.abs() > 1e-9).ok_or_else(|| bad(cmd, "`distance` must be a non-zero number"))?;
     let side = p.get("side").and_then(vec2);
     let use_chain = bool_(p, "chain").unwrap_or(true);
-    let (out, info) = edit(s, p, cmd, true, |sk, doc| {
+    // Both sides at once. The words keep the meaning `solid.extrude` gives them: `symmetric` is
+    // one distance applied each way, `distance2` is an independent distance the other way.
+    let symmetric = match str_(p, "direction").map(str::to_ascii_lowercase).as_deref() {
+        None | Some("positive") | Some("one_side") => bool_(p, "symmetric").unwrap_or(false),
+        Some("symmetric") => true,
+        Some("negative" | "reverse" | "flip") => {
+            return Err(bad(cmd, "an offset has no negative direction: give a negative `distance`, or a `side` to offset toward"));
+        }
+        Some(other) => return Err(bad(cmd, format!("unknown direction `{other}` (one_side, symmetric)"))),
+    };
+    let distance2 = match p.get("distance2") {
+        None => None,
+        Some(_) => Some(num(p, "distance2").filter(|d| *d > 1e-9).ok_or_else(|| {
+            bad(
+                cmd,
+                "`distance2` must be a positive number: the other side's distance (the sign of `distance`, or `side`, picks which side is which)",
+            )
+        })?),
+    };
+    if symmetric && distance2.is_some() {
+        return Err(bad(cmd, "give `distance2` or `symmetric`, not both"));
+    }
+    if symmetric && side.is_some() {
+        return Err(bad(cmd, "`symmetric` offsets both sides, so `side` has no side left to pick: drop one of them"));
+    }
+    let (sides, info) = edit(s, p, cmd, true, |sk, doc| {
         sk.refresh_offsets()?;
         let rep = solve_current(sk, doc)?;
         if !rep.keeps_orientation() {
@@ -945,30 +1117,42 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
                 "offsets of a boundary with retired corner arcs are not supported yet; break its offset association to use the current fixed topology",
             ));
         }
-        let mut made = Vec::new();
-        let mut cons = Vec::new();
-        // Circles offset on their own.
+        let mut sides: Vec<Side> = Vec::new();
+        // Circles offset on their own, concentrically. Both sides are then a smaller circle and
+        // a larger one; the one toward the centre still has to have a size.
         if let Some(CurveKind::Circle { c, r }) = sk.curves.get(first).map(|c| c.kind.clone()) {
             let cc = sk.point(c).unwrap_or_default();
+            let source = sk.curves.get(first).map(|c| c.id.clone()).ok_or_else(|| bad(cmd, "offset source circle vanished"))?;
             let grow = match side {
                 Some(q) => q.dist(cc) > r,
                 None => d0 < 0.0,
             };
-            let nr = if grow { r + d0.abs() } else { r - d0.abs() };
-            if nr <= 1e-9 {
-                return Err(bad(cmd, "the offset circle would have no size"));
+            let radii: Vec<f64> = match (symmetric, distance2) {
+                (true, _) => vec![r - d0.abs(), r + d0.abs()],
+                (_, Some(second)) if grow => vec![r + d0.abs(), r - second],
+                (_, Some(second)) => vec![r - d0.abs(), r + second],
+                _ if grow => vec![r + d0.abs()],
+                _ => vec![r - d0.abs()],
+            };
+            for nr in radii {
+                if nr <= 1e-9 {
+                    return Err(bad(cmd, "the offset circle would have no size"));
+                }
+                let ci = sk.add_circle(cc, nr, Some(c), None)?;
+                let outputs = ids_of(sk, &[ci]);
+                sk.offsets.push(solidcraft_sketch::OffsetChain {
+                    sources: vec![(source.clone(), true)],
+                    outputs: outputs.clone(),
+                    distance: r - nr,
+                    closed: true,
+                    topology: None,
+                });
+                sides.push(Side { distance: r - nr, curves: outputs, constraints: Vec::new(), association: None });
             }
-            let ci = sk.add_circle(cc, nr, Some(c), None)?;
-            made.push(ci);
-            sk.offsets.push(solidcraft_sketch::OffsetChain {
-                sources: vec![(ids[0].clone(), true)],
-                outputs: ids_of(sk, &made),
-                distance: r - nr,
-                closed: true,
-                topology: None,
-            });
-            return Ok((ids_of(sk, &made), cons, None));
+            return Ok(sides);
         }
+        // The chain is walked once, before anything is created: a second side has to follow the
+        // same source curves, not a pool the first side has already added its output to.
         let pool: Vec<usize> = if use_chain {
             (0..sk.curves.len())
                 .filter(|i| sk.curves.get(*i).is_some_and(|c| c.construction == sk.curves.get(first).is_some_and(|f| f.construction)))
@@ -989,6 +1173,7 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
             }
             None => d0,
         };
+        let runs = offset_runs(d, symmetric, distance2);
         if order.iter().any(|(i, _)| sk.shape(*i).is_none()) {
             // A smooth free-form entity is offset from exact pieces. Junctions that
             // would require trimming/intersecting independent normal offsets are
@@ -996,9 +1181,12 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
             if order.len() != 1 {
                 return Err(bad(cmd, "offset smooth free-form curves individually; mixed chain junctions are ambiguous"));
             }
-            let (source, forward) = order[0];
-            let output = sk.add_freeform_offset(source, forward, d)?;
-            return Ok((ids_of(sk, &[output]), cons, None));
+            let (source, forward) = *order.first().ok_or_else(|| bad(cmd, "no curves"))?;
+            for dd in runs {
+                let output = sk.add_freeform_offset(source, forward, dd)?;
+                sides.push(Side { distance: dd, curves: ids_of(sk, &[output]), constraints: Vec::new(), association: None });
+            }
+            return Ok(sides);
         }
         let sources = order
             .iter()
@@ -1006,115 +1194,30 @@ fn offset(s: &mut Session, p: &Value) -> Result<Value> {
                 sk.curves.get(*index).map(|curve| (curve.id.clone(), *forward)).ok_or_else(|| bad(cmd, "offset chain source vanished"))
             })
             .collect::<Result<Vec<_>>>()?;
-        if closed && sk.convex_offset_supported(&sources)? {
-            let created = sk.add_convex_offset(sources.clone(), d)?;
-            let roles = sk
-                .offsets
-                .iter()
-                .filter_map(|offset| offset.topology.as_ref())
-                .find(|topology| topology.id == created.association)
-                .map(|topology| topology.roles.clone())
-                .ok_or_else(|| bad(cmd, "new offset association is missing"))?;
-            for (source, role) in sources.iter().zip(&roles) {
-                if role.kind == solidcraft_sketch::OffsetRoleKind::Line {
-                    let a = sk.curve_index(&source.0).ok_or_else(|| bad(cmd, "offset source line vanished"))?;
-                    let b = sk.curve_index(&role.output).ok_or_else(|| bad(cmd, "offset output line vanished"))?;
-                    cons.push(add_c(sk, ConstraintKind::Parallel { a, b })?);
-                }
-            }
-            return Ok((created.curves, cons, Some(created.association)));
+        let convex = closed && sk.convex_offset_supported(&sources)?;
+        for dd in runs {
+            sides.push(offset_side(sk, cmd, &order, &sources, closed, convex, dd)?);
         }
-        let pieces: Vec<Piece> =
-            order.iter().map(|(c, f)| offset_piece(sk, *c, *f, d)).collect::<Option<_>>().ok_or_else(|| bad(cmd, "the offset collapses an arc"))?;
-        let n = pieces.len();
-        let start_of = |p: &Piece| match p {
-            Piece::Line(a, _) => *a,
-            Piece::Arc(_, _, _, s, _, _) => *s,
-            Piece::Free(v) => v.first().copied().unwrap_or_default(),
-        };
-        let end_of = |p: &Piece| match p {
-            Piece::Line(_, b) => *b,
-            Piece::Arc(_, _, _, _, e, _) => *e,
-            Piece::Free(v) => v.last().copied().unwrap_or_default(),
-        };
-        // Junction points between consecutive pieces.
-        let joint = |x: &Piece, y: &Piece| -> Vec2 {
-            let (e, s0) = (end_of(x), start_of(y));
-            if e.dist(s0) < TOL * 10.0 {
-                return e;
-            }
-            let guess = (e + s0) * 0.5;
-            if matches!(x, Piece::Free(_)) || matches!(y, Piece::Free(_)) {
-                return guess;
-            }
-            intersections(&piece_shape(x), &piece_shape(y)).into_iter().min_by(|a, b| a.dist(guess).total_cmp(&b.dist(guess))).unwrap_or(guess)
-        };
-        let mut joints: Vec<Vec2> = Vec::new();
-        joints.push(if closed { joint(&pieces[n - 1], &pieces[0]) } else { start_of(&pieces[0]) });
-        for k in 0..n.saturating_sub(1) {
-            joints.push(joint(&pieces[k], &pieces[k + 1]));
-        }
-        if !closed {
-            joints.push(end_of(&pieces[n - 1]));
-        }
-        // A straight piece whose joints come out reversed (or meet) was overrun by its
-        // neighbours: the offset is larger than the shape allows there.
-        for (k, pc) in pieces.iter().enumerate() {
-            if let Piece::Line(a, b) = pc {
-                let (ja, jb) = (joints.get(k).copied(), joints.get(if closed { (k + 1) % n } else { k + 1 }).copied());
-                if let (Some(ja), Some(jb)) = (ja, jb)
-                    && (jb - ja).dot(*b - *a) <= TOL * a.dist(*b)
-                {
-                    return Err(bad(cmd, "the offset is larger than the shape allows (the offset curves would cross)"));
-                }
-            }
-        }
-        let pts: Vec<usize> = joints.iter().map(|q| sk.add_point(*q, None)).collect::<std::result::Result<_, _>>()?;
-        for (k, pc) in pieces.iter().enumerate() {
-            let (pa, pb) = (pts[k], if closed { pts[(k + 1) % n] } else { pts[k + 1] });
-            let (orig, _) = order[k];
-            match pc.clone() {
-                Piece::Free(v) => {
-                    // A fit spline through a few of the samples, ending at the joints.
-                    let step = (v.len() / 24).max(1);
-                    let mut idx = vec![pa];
-                    for q in v.iter().skip(step).step_by(step) {
-                        if q.dist(*v.last().unwrap_or(q)) > 1e-6 {
-                            idx.push(sk.add_point(*q, None)?);
-                        }
-                    }
-                    idx.push(pb);
-                    idx.dedup();
-                    if idx.len() >= 2 {
-                        made.push(sk.add_curve(CurveKind::Spline { pts: idx, control: false, degree: 3, periodic: false }, None)?);
-                    }
-                }
-                Piece::Line(..) => {
-                    let l = sk.add_line_pts(pa, pb, None)?;
-                    cons.push(add_c(sk, ConstraintKind::Parallel { a: orig, b: l })?);
-                    made.push(l);
-                }
-                Piece::Arc(ci, cc, _, _, _, ccw) => {
-                    let (qa, qb) = (sk.point(pa).unwrap_or_default(), sk.point(pb).unwrap_or_default());
-                    let a = if ccw {
-                        sk.add_arc(cc, qa, qb, [Some(ci), Some(pa), Some(pb)], None)?
-                    } else {
-                        sk.add_arc(cc, qb, qa, [Some(ci), Some(pb), Some(pa)], None)?
-                    };
-                    made.push(a);
-                }
-            }
-        }
-        let outputs = ids_of(sk, &made);
-        if pieces.iter().all(|p| !matches!(p, Piece::Free(_))) {
-            let sources = order.iter().filter_map(|(i, forward)| sk.curves.get(*i).map(|c| (c.id.clone(), *forward))).collect();
-            sk.offsets.push(solidcraft_sketch::OffsetChain { sources, outputs: outputs.clone(), distance: d, closed, topology: None });
-            sk.refresh_offsets()?;
-        }
-        Ok((outputs, cons, None))
+        Ok(sides)
     })?;
-    let mut response = json!({"curves":out.0,"constraints":out.1,"sketch":info});
-    if let Some(association) = out.2 {
+    let curves: Vec<&String> = sides.iter().flat_map(|side| side.curves.iter()).collect();
+    let constraints: Vec<&String> = sides.iter().flat_map(|side| side.constraints.iter()).collect();
+    let each: Vec<Value> = sides
+        .iter()
+        .map(|side| {
+            let mut entry = json!({"distance": side.distance, "curves": side.curves});
+            if let Some(association) = &side.association {
+                entry["association"] = json!(association);
+            }
+            entry
+        })
+        .collect();
+    let mut response = json!({"curves":curves,"constraints":constraints,"sketch":info,"sides":each});
+    // One side keeps the single `association` it always returned. Two sides have one each, in
+    // `sides`, so there is no single association left to name.
+    if let [only] = sides.as_slice()
+        && let Some(association) = &only.association
+    {
         response["association"] = json!(association);
     }
     Ok(response)

crates/engine/src/cmd/sketch_modify_tests.rs

@@ -1018,3 +1018,184 @@ fn periodic_offset_extrusion_survives_post_extrude_span_changes_and_cold_reopen(
         run(&mut s, "edit.undo", json!({}));
     }
 }
+
+/// The bounding box of a set of sketch curves, from their polylines.
+fn bounds(sk: &solidcraft_sketch::Sketch, curves: &[String]) -> (Vec2, Vec2) {
+    let mut lo = Vec2::new(f64::INFINITY, f64::INFINITY);
+    let mut hi = Vec2::new(f64::NEG_INFINITY, f64::NEG_INFINITY);
+    for id in curves {
+        let i = sk.curve_index(id).unwrap();
+        for p in sk.polyline(i) {
+            lo = Vec2::new(lo.x.min(p.x), lo.y.min(p.y));
+            hi = Vec2::new(hi.x.max(p.x), hi.y.max(p.y));
+        }
+    }
+    (lo, hi)
+}
+
+fn box_is(sk: &solidcraft_sketch::Sketch, curves: &[String], lo: [f64; 2], hi: [f64; 2]) -> bool {
+    let (a, b) = bounds(sk, curves);
+    a.dist(Vec2::new(lo[0], lo[1])) < 1e-6 && b.dist(Vec2::new(hi[0], hi[1])) < 1e-6
+}
+
+fn side_curves(v: &Value, i: usize) -> Vec<String> {
+    ids(&v["sides"][i]["curves"])
+}
+
+#[test]
+fn offset_symmetric_puts_the_same_distance_on_both_sides_of_a_chain() {
+    let mut s = new_sketch();
+    let r = run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [40, 30]}));
+    let l = ids(&r["curves"]);
+    // A 40 by 30 rectangle offset symmetrically by 5: one chain 5 inside (5,5)-(35,25), a
+    // 30 by 20 rectangle, and one 5 outside (-5,-5)-(45,35), a 50 by 40 rectangle.
+    let o = run(&mut s, "sketch.offset", json!({"curves": [l[0]], "distance": 5, "symmetric": true}));
+    assert_eq!(o["sides"].as_array().map(Vec::len), Some(2), "{o}");
+    assert_eq!(ids(&o["curves"]).len(), 8, "{o}");
+    let (a, b) = (side_curves(&o, 0), side_curves(&o, 1));
+    assert_eq!((a.len(), b.len()), (4, 4), "{o}");
+    let sk = sketch(&s);
+    // The chain's walk direction decides which side is first, so match on the sizes.
+    let inner = box_is(&sk, &a, [5.0, 5.0], [35.0, 25.0]) && box_is(&sk, &b, [-5.0, -5.0], [45.0, 35.0]);
+    let outer = box_is(&sk, &b, [5.0, 5.0], [35.0, 25.0]) && box_is(&sk, &a, [-5.0, -5.0], [45.0, 35.0]);
+    assert!(inner || outer, "{:?} {:?}", bounds(&sk, &a), bounds(&sk, &b));
+    // The two distances are equal and opposite.
+    let d: Vec<f64> = o["sides"].as_array().unwrap().iter().map(|x| x["distance"].as_f64().unwrap()).collect();
+    assert!(close(d[0], -d[1]) && close(d[0].abs(), 5.0), "{d:?}");
+    // Both sides are parallel to their sources, so each one added four constraints.
+    assert_eq!(ids(&o["constraints"]).len(), 8, "{o}");
+}
+
+#[test]
+fn offset_two_sides_takes_an_independent_distance_the_other_way() {
+    let mut s = new_sketch();
+    let r = run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [40, 30]}));
+    let l = ids(&r["curves"]);
+    // `side` sends `distance` 5 inward, so `distance2` 3 goes outward: (5,5)-(35,25), a 30 by
+    // 20 rectangle, and (-3,-3)-(43,33), a 46 by 36 one.
+    let o = run(&mut s, "sketch.offset", json!({"curves": [l[0]], "distance": 5, "distance2": 3, "side": [20, 15]}));
+    assert_eq!(o["sides"].as_array().map(Vec::len), Some(2), "{o}");
+    let sk = sketch(&s);
+    assert!(box_is(&sk, &side_curves(&o, 0), [5.0, 5.0], [35.0, 25.0]), "{:?}", bounds(&sk, &side_curves(&o, 0)));
+    assert!(box_is(&sk, &side_curves(&o, 1), [-3.0, -3.0], [43.0, 33.0]), "{:?}", bounds(&sk, &side_curves(&o, 1)));
+}
+
+#[test]
+fn offset_two_sides_of_one_curve_follows_the_sign_of_the_distance() {
+    let mut s = new_sketch();
+    let r = run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [40, 30]}));
+    let l = ids(&r["curves"]);
+    // The bottom edge runs (0,0)-(40,0). Chain off, distance -5 and distance2 3: one line at
+    // y = -5 and one at y = 3, each 40 long.
+    let f = run(&mut s, "sketch.offset", json!({"curves": [l[0]], "distance": -5, "distance2": 3, "chain": false}));
+    assert_eq!(f["sides"].as_array().map(Vec::len), Some(2), "{f}");
+    let sk = sketch(&s);
+    let (one, two) = (bounds(&sk, &side_curves(&f, 0)), bounds(&sk, &side_curves(&f, 1)));
+    assert!(close(one.0.y, one.1.y) && close(two.0.y, two.1.y), "{one:?} {two:?}");
+    assert!(close(one.0.y, -5.0) && close(two.0.y, 3.0), "{one:?} {two:?}");
+    assert!(close(one.1.x - one.0.x, 40.0) && close(two.1.x - two.0.x, 40.0), "{one:?} {two:?}");
+}
+
+#[test]
+fn offset_both_sides_of_a_rounded_boundary_keep_separate_associations() {
+    let mut s = new_sketch();
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [-38, -33], "p1": [38, 33]}));
+    run(&mut s, "sketch.fillet", json!({"points": ["l1.start", "l1.end", "l2.end", "l3.end"], "radius": "1 mm"}));
+    // A 76 by 66 boundary with 1 mm corners, offset symmetrically by 0.2: 75.6 by 65.6 with
+    // 0.8 mm corners inside, and 76.4 by 66.4 with 1.2 mm corners outside.
+    let o = run(&mut s, "sketch.offset", json!({"curves": ["l1"], "distance": 0.2, "symmetric": true}));
+    let sides = o["sides"].as_array().unwrap().clone();
+    assert_eq!(sides.len(), 2, "{o}");
+    // Each side is its own offset association; a single side still reports the one it always did.
+    let associations: Vec<&str> = sides.iter().filter_map(|x| x["association"].as_str()).collect();
+    assert_eq!(associations.len(), 2, "{o}");
+    assert_ne!(associations[0], associations[1], "{o}");
+    assert!(o["association"].is_null(), "two sides name no single association: {o}");
+    let sk = sketch(&s);
+    assert_eq!(sk.offsets.len(), 2);
+    for association in &associations {
+        assert_eq!(sk.offset_boundary(association).unwrap().len(), 8, "{association}");
+    }
+    let radii = |curves: &[String]| {
+        let mut r: Vec<f64> = curves
+            .iter()
+            .filter_map(|id| {
+                let CurveKind::Arc { c, a, .. } = sk.curves.get(sk.curve_index(id)?)?.kind else { return None };
+                Some(sk.point(c)?.dist(sk.point(a)?))
+            })
+            .collect();
+        r.sort_by(f64::total_cmp);
+        r
+    };
+    let (a, b) = (side_curves(&o, 0), side_curves(&o, 1));
+    let (ra, rb) = (radii(&a), radii(&b));
+    assert_eq!((ra.len(), rb.len()), (4, 4), "{ra:?} {rb:?}");
+    let shrunk = ra.iter().all(|r| close(*r, 0.8)) && rb.iter().all(|r| close(*r, 1.2));
+    let grown = rb.iter().all(|r| close(*r, 0.8)) && ra.iter().all(|r| close(*r, 1.2));
+    assert!(shrunk || grown, "{ra:?} {rb:?}");
+    let small = if shrunk { &a } else { &b };
+    let large = if shrunk { &b } else { &a };
+    assert!(box_is(&sk, small, [-37.8, -32.8], [37.8, 32.8]), "{:?}", bounds(&sk, small));
+    assert!(box_is(&sk, large, [-38.2, -33.2], [38.2, 33.2]), "{:?}", bounds(&sk, large));
+}
+
+#[test]
+fn offset_both_sides_of_a_circle_are_concentric() {
+    let mut s = new_sketch();
+    let c = ids(&run(&mut s, "sketch.circle.center", json!({"center": [0, 0], "radius": 10}))["curves"])[0].clone();
+    // Symmetric by 3 on a 10 mm circle: a 7 mm circle and a 13 mm one, both about the centre.
+    let o = run(&mut s, "sketch.offset", json!({"curves": [c], "distance": 3, "symmetric": true}));
+    let sk = sketch(&s);
+    let radius = |id: &str| match sk.curves.get(sk.curve_index(id).unwrap()).unwrap().kind {
+        CurveKind::Circle { c, r } => (sk.point(c).unwrap(), r),
+        _ => panic!("not a circle"),
+    };
+    let made = ids(&o["curves"]);
+    assert_eq!(made.len(), 2, "{o}");
+    let (p0, r0) = radius(&made[0]);
+    let (p1, r1) = radius(&made[1]);
+    assert!(p0.dist(Vec2::default()) < 1e-9 && p1.dist(Vec2::default()) < 1e-9);
+    assert!(close(r0, 7.0) && close(r1, 13.0), "{r0} {r1}");
+    // A circle whose inward side would be offset away to nothing is refused, both sides with it.
+    assert!(s.execute("sketch.offset", &json!({"curves": [c], "distance": 10, "symmetric": true})).is_err());
+}
+
+#[test]
+fn offset_refuses_the_combinations_that_would_be_guesswork() {
+    let mut s = new_sketch();
+    let r = run(&mut s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [40, 30]}));
+    let l = ids(&r["curves"]);
+    let refused = |s: &mut Session, p: Value| s.execute("sketch.offset", &p).unwrap_err().to_string();
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "symmetric": true, "side": [20, 15]}));
+    assert!(e.contains("no side left to pick"), "{e}");
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "symmetric": true, "distance2": 3}));
+    assert!(e.contains("`distance2` or `symmetric`"), "{e}");
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "distance2": -3}));
+    assert!(e.contains("`distance2` must be a positive number"), "{e}");
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "distance2": 0}));
+    assert!(e.contains("`distance2` must be a positive number"), "{e}");
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "direction": "negative"}));
+    assert!(e.contains("no negative direction"), "{e}");
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 5, "direction": "sideways"}));
+    assert!(e.contains("unknown direction"), "{e}");
+    // An inward side the shape cannot hold refuses the whole command, the outward side with it.
+    let e = refused(&mut s, json!({"curves": [l[0]], "distance": 20, "symmetric": true}));
+    assert!(e.contains("larger than the shape allows"), "{e}");
+    assert_eq!(sketch(&s).curves.len(), 4, "a refused offset leaves the sketch alone");
+    // `direction: symmetric` is the word `solid.extrude` uses, and it means the same here.
+    let o = run(&mut s, "sketch.offset", json!({"curves": [l[0]], "distance": 5, "direction": "symmetric"}));
+    assert_eq!(o["sides"].as_array().map(Vec::len), Some(2), "{o}");
+}
+
+#[test]
+fn offset_one_side_still_reports_one_set_of_curves_and_its_association() {
+    let mut s = new_sketch();
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [-38, -33], "p1": [38, 33]}));
+    run(&mut s, "sketch.fillet", json!({"points": ["l1.start", "l1.end", "l2.end", "l3.end"], "radius": "1 mm"}));
+    let o = run(&mut s, "sketch.offset", json!({"curves": ["l1"], "distance": 0.2, "side": [0, 0]}));
+    assert_eq!(o["sides"].as_array().map(Vec::len), Some(1), "{o}");
+    let association = o["association"].as_str().unwrap().to_string();
+    assert_eq!(o["sides"][0]["association"].as_str(), Some(association.as_str()), "{o}");
+    assert_eq!(ids(&o["curves"]), ids(&o["sides"][0]["curves"]), "{o}");
+    assert!(close(o["sides"][0]["distance"].as_f64().unwrap().abs(), 0.2), "{o}");
+}

crates/ui-egui/src/canvas.rs

@@ -53,9 +53,10 @@ pub fn anchor(app: &SolveApp, d: &Dialog) -> Option<(Vec3, Option<Vec3>)> {
             let (mid, tangent) = poly_mid(&pts)?;
             // An offset's drag arrow: the in-plane direction the distance grows along. The
             // command offsets a picked curve to its left, and the window's Flip row reverses it.
+            // Symmetric hides Flip and offsets both ways, so the arrow keeps the left side.
             let dir = match &d.kind {
-                Kind::SketchModify(crate::sketch_modify_ui::Mod::Offset { flip, .. }) => {
-                    let n = if *flip { -tangent.perp() } else { tangent.perp() };
+                Kind::SketchModify(crate::sketch_modify_ui::Mod::Offset { flip, mode, .. }) => {
+                    let n = if *flip && !crate::sketch_modify_ui::offset_symmetric(*mode) { -tangent.perp() } else { tangent.perp() };
                     Some(ss.plane.to_world(mid + n) - ss.plane.to_world(mid))
                 }
                 _ => None,

crates/ui-egui/src/icons.rs

@@ -937,6 +937,23 @@ pub fn paint(p: &Painter, r: Rect, name: &str, ink: Color32, fill: Color32, acce
             pen.arc(8.0, 15.0, 5.0, std::f32::consts::PI, std::f32::consts::PI * 1.5, a);
             pen.arc(8.0, 9.0, 5.0, std::f32::consts::FRAC_PI_2, std::f32::consts::PI, a);
         }
+        // Offset mode icons, drawn with the house `dashed` helper. The source is the solid
+        // line and each result a dashed one. One Side has a single result; Two Sides has one
+        // each way at two different gaps; Symmetric has one each way at the same gap.
+        "offset_one_side" => {
+            pen.line(&[(8.0, 4.0), (8.0, 20.0)], ink);
+            pen.dashed(&[(18.0, 4.0), (18.0, 20.0)], a);
+        }
+        "offset_two_sides" => {
+            pen.line(&[(13.0, 4.0), (13.0, 20.0)], ink);
+            pen.dashed(&[(3.0, 4.0), (3.0, 20.0)], a);
+            pen.dashed(&[(20.0, 4.0), (20.0, 20.0)], a);
+        }
+        "offset_symmetric" => {
+            pen.line(&[(12.0, 4.0), (12.0, 20.0)], ink);
+            pen.dashed(&[(4.0, 4.0), (4.0, 20.0)], a);
+            pen.dashed(&[(20.0, 4.0), (20.0, 20.0)], a);
+        }
         "trim" => {
             pen.line(&[(12.0, 3.0), (12.0, 21.0)], ink);
             pen.line(&[(3.0, 12.0), (12.0, 12.0)], ink);

crates/ui-egui/src/sketch_modify_ui.rs

@@ -4,7 +4,8 @@
 //! reached no tool and no dialog at all, so a press ran `sketch.scale` with no parameters and
 //! the engine answered "`factor` must be a positive number". Offset joins it here (upstream
 //! issue #162 item 1: "Offset does not create a constraint, the size of the offset seems
-//! random"). Mirror joins them here, which ran as a bare click flow: entities until a
+//! random"), and it now offers the same One Side, Two Sides and Symmetric directions
+//! `solid.extrude` already names. Mirror joins them here, which ran as a bare click flow: entities until a
 //! right-click, then one more click for the line, with nothing on screen saying what was
 //! picked. Move joins them too, which had no toolbar placement, no tool and no dialog: its only
 //! route into the UI was the sketch context menu, and that went through the same
@@ -39,6 +40,21 @@ const CHAMFER_TYPE_ICONS: [&str; 3] = ["sketch_chamfer_equal", "sketch_chamfer_t
 /// The engine's own cap on the copies one sketch pattern may make.
 const MAX_COPIES: f64 = 500.0;
 
+/// The offset directions, in the words and the order `solid.extrude` already uses for them.
+/// One Side offsets the way the distance points. Two Sides adds an independent distance the
+/// other way. Symmetric applies the one distance each way.
+pub(crate) const OFFSET_MODES: [&str; 3] = ["One Side", "Two Sides", "Symmetric"];
+const OFFSET_MODE_ICONS: [&str; 3] = ["offset_one_side", "offset_two_sides", "offset_symmetric"];
+/// Index of Two Sides in [`OFFSET_MODES`] (the mode with a second distance).
+const TWO_SIDES: usize = 1;
+/// Index of Symmetric in [`OFFSET_MODES`].
+const SYMMETRIC: usize = 2;
+
+/// Whether an offset mode index is Symmetric (which hides Flip and offsets both ways).
+pub(crate) fn offset_symmetric(mode: usize) -> bool {
+    mode == SYMMETRIC
+}
+
 /// A sketch modify tool window's values.
 #[derive(Clone, Debug, PartialEq)]
 pub enum Mod {
@@ -48,8 +64,9 @@ pub enum Mod {
     Scale { factor: String },
     /// `sketch.offset`: the curves to offset, the distance typed and whether the connected
     /// chain follows. A positive distance is left of the chain, as the command defines it;
-    /// `flip` reverses whatever sign the field holds.
-    Offset { distance: String, chain: bool, flip: bool },
+    /// `flip` reverses whatever sign the field holds. `mode` indexes [`OFFSET_MODES`], and
+    /// `distance2` is the other side's distance that Two Sides asks for.
+    Offset { distance: String, distance2: String, mode: usize, chain: bool, flip: bool },
     /// `sketch.mirror`: the entities and the line they reflect in. The command has no number of
     /// its own, so the window's whole job is to show what is picked and let a pick be changed
     /// before anything is committed.
@@ -126,7 +143,7 @@ pub fn start(_app: &SolveApp, id: &str) -> Option<(Kind, Vec<SelInput>)> {
     };
     let k = match id {
         "sketch.scale" => Mod::Scale { factor: "2".into() },
-        "sketch.offset" => Mod::Offset { distance: "2 mm".into(), chain: true, flip: false },
+        "sketch.offset" => Mod::Offset { distance: "2 mm".into(), distance2: "2 mm".into(), mode: 0, chain: true, flip: false },
         "sketch.mirror" => Mod::Mirror,
         "sketch.move" => Mod::Move { x: "0 mm".into(), y: "0 mm".into(), angle: "0 deg".into(), copy: false },
         "sketch.pattern.rectangular" => Mod::PatternRect { count: "3".into(), spacing: "20 mm".into(), count2: "1".into(), spacing2: "20 mm".into() },
@@ -149,13 +166,24 @@ pub fn rows(ui: &mut egui::Ui, k: &mut Mod) -> bool {
             enter |= field(ui, factor);
             ui.end_row();
         }
-        Mod::Offset { distance, chain, flip } => {
+        Mod::Offset { distance, distance2, mode, chain, flip } => {
+            row_label(ui, "Direction");
+            icon_choice(ui, &OFFSET_MODES, &OFFSET_MODE_ICONS, mode);
+            ui.end_row();
             row_label(ui, "Distance");
             enter |= field(ui, distance);
             ui.end_row();
-            row_label(ui, "Flip");
-            check(ui, flip);
-            ui.end_row();
+            if *mode == TWO_SIDES {
+                row_label(ui, "Distance 2");
+                enter |= field(ui, distance2);
+                ui.end_row();
+            }
+            // Symmetric offsets both sides, so there is no side left for Flip to swap.
+            if *mode != SYMMETRIC {
+                row_label(ui, "Flip");
+                check(ui, flip);
+                ui.end_row();
+            }
             row_label(ui, "Chain");
             check(ui, chain);
             ui.end_row();
@@ -330,11 +358,11 @@ fn value(app: &SolveApp, text: &str, kind: ValueKind, label: &str) -> Result<f64
 /// A typed distance as the command wants it: the field evaluated against the document's
 /// parameters, with the sign reversed when Flip is set. A bare number means the design's units,
 /// as a typed sketch value does everywhere else.
-fn signed_length(app: &SolveApp, text: &str, flip: bool) -> Result<f64, String> {
+fn signed_length(app: &SolveApp, label: &str, text: &str, flip: bool) -> Result<f64, String> {
     let doc = &app.session.doc;
-    let v = doc.eval(&doc.with_design_unit(text.trim(), ValueKind::Length), ValueKind::Length).map_err(|e| format!("Distance: {e}"))?;
+    let v = doc.eval(&doc.with_design_unit(text.trim(), ValueKind::Length), ValueKind::Length).map_err(|e| format!("{label}: {e}"))?;
     if !v.is_finite() || v.abs() <= 1e-9 {
-        return Err("Distance must be a non-zero number".into());
+        return Err(format!("{label} must be a non-zero number"));
     }
     Ok(if flip { -v } else { v })
 }
@@ -430,13 +458,23 @@ pub fn commands(app: &SolveApp, k: &Mod, inputs: &[SelInput], extra: &Map<String
             }
             ("sketch.scale", p)
         }
-        Mod::Offset { distance, chain, flip } => {
+        Mod::Offset { distance, distance2, mode, chain, flip } => {
             let curves = curve_ids(inputs, 0);
             if curves.is_empty() {
                 return Err("Select the curves to offset first".into());
             }
-            let d = signed_length(app, distance, *flip)?;
-            ("sketch.offset", json!({"curves": curves, "distance": d, "chain": chain}))
+            // Symmetric hides Flip, so a flip left over from another mode does not travel with it.
+            let d = signed_length(app, "Distance", distance, *flip && *mode != SYMMETRIC)?;
+            let mut params = json!({"curves": curves, "distance": d, "chain": chain});
+            if let Value::Object(m) = &mut params {
+                if *mode == SYMMETRIC {
+                    m.insert("symmetric".into(), json!(true));
+                }
+                if *mode == TWO_SIDES {
+                    m.insert("distance2".into(), json!(signed_length(app, "Distance 2", distance2, false)?.abs()));
+                }
+            }
+            ("sketch.offset", params)
         }
         Mod::Mirror => {
             let entities = entity_ids(inputs, 0);

crates/ui-egui/tests/scenarios/sketch_offset_two_sides.json

@@ -0,0 +1,83 @@
+[
+ {"note": "Offset had one distance and one direction, so there was no way to offset both sides of a curve in one operation. The window gains a Direction row of icon buttons carrying One Side, Two Sides and Symmetric, in the words solid.extrude already uses. Symmetric applies one distance each way. Two Sides adds an independent Distance 2 the other way."},
+ {"start": "sketch.create"},
+ {"click": {"plane": "XY"}},
+ {"expect": {"sketching": true}},
+ {"start": "sketch.circle.center"},
+ {"click": {"sketch": [0, 0]}},
+ {"click": {"sketch": [10, 0]}},
+ {"key": "Escape"},
+ {"expect": {"sketch_curves": {"own": 1}, "errors": 0}},
+
+ {"note": "The window opens on One Side: Flip is offered, Distance 2 is not."},
+ {"start": "sketch.offset"},
+ {"click": {"sketch": [10, 0]}},
+ {"expect": {"dialog": "Offset", "shown_handles": ["dialog:Direction", "dialog:Distance", "dialog:Flip", "dialog:Chain"], "hidden_handles": ["dialog:Distance 2"]}},
+
+ {"note": "Symmetric offsets both sides, so Flip has no side left to swap and the row goes."},
+ {"click": {"handle": "dialog:Direction:Symmetric"}},
+ {"expect": {"dialog": "Offset", "shown_handles": ["dialog:Distance", "dialog:Chain"], "hidden_handles": ["dialog:Flip", "dialog:Distance 2"]}},
+
+ {"note": "A 10 mm circle offset symmetrically by a typed 3 mm becomes a 7 mm circle and a 13 mm one, both about the same centre."},
+ {"click": {"handle": "dialog:Distance"}},
+ {"key": "A", "cmd": true},
+ {"text": "3"},
+ {"key": "Enter"},
+ {"expect": {"dialog": null, "errors": 0, "sketch_curves": {"own": 3}}},
+ {"expect": {"query": {"command": "sketch.inspect", "path": ["curves", 1, "radius"], "value": 7}}},
+ {"expect": {"query": {"command": "sketch.inspect", "path": ["curves", 2, "radius"], "value": 13}}},
+ {"shot": "sketch_offset_symmetric_circle"},
+ {"start": "sketch.finish"},
+
+ {"note": "Two Sides asks for the second distance, and Flip comes back: it decides which side each distance lands on."},
+ {"start": "sketch.create"},
+ {"click": {"plane": "XZ"}},
+ {"start": "sketch.circle.center"},
+ {"click": {"sketch": [0, 0]}},
+ {"click": {"sketch": [10, 0]}},
+ {"key": "Escape"},
+ {"expect": {"sketch_curves": {"own": 1}, "errors": 0}},
+ {"start": "sketch.offset"},
+ {"click": {"sketch": [10, 0]}},
+ {"click": {"handle": "dialog:Direction:Two Sides"}},
+ {"expect": {"dialog": "Offset", "shown_handles": ["dialog:Distance", "dialog:Distance 2", "dialog:Flip", "dialog:Chain"]}},
+
+ {"note": "Distance 3 inward and Distance 2 of 5 outward on the same 10 mm circle: a 7 mm circle and a 15 mm one."},
+ {"click": {"handle": "dialog:Distance"}},
+ {"key": "A", "cmd": true},
+ {"text": "3"},
+ {"click": {"handle": "dialog:Distance 2"}},
+ {"key": "A", "cmd": true},
+ {"text": "5"},
+ {"key": "Enter"},
+ {"expect": {"dialog": null, "errors": 0, "sketch_curves": {"own": 3}}},
+ {"expect": {"query": {"command": "sketch.inspect", "path": ["curves", 1, "radius"], "value": 7}}},
+ {"expect": {"query": {"command": "sketch.inspect", "path": ["curves", 2, "radius"], "value": 15}}},
+ {"start": "sketch.finish"},
+
+ {"note": "A whole chain offsets both ways at once: one picked edge of a 40 by 30 rectangle, symmetric by 5, gives a 30 by 20 chain inside and a 50 by 40 chain outside, four curves each."},
+ {"start": "sketch.create"},
+ {"click": {"plane": "YZ"}},
+ {"start": "sketch.rectangle.two_point"},
+ {"click": {"sketch": [0, 0]}},
+ {"click": {"sketch": [40, 30]}},
+ {"key": "Escape"},
+ {"expect": {"sketch_curves": {"own": 4}, "errors": 0}},
+ {"start": "sketch.offset"},
+ {"click": {"sketch": [20, 0]}},
+ {"click": {"handle": "dialog:Direction:Symmetric"}},
+ {"click": {"handle": "dialog:Distance"}},
+ {"key": "A", "cmd": true},
+ {"text": "5"},
+ {"key": "Enter"},
+ {"expect": {"dialog": null, "errors": 0, "sketch_curves": {"own": 12}}},
+ {"shot": "sketch_offset_symmetric_chain"},
+
+ {"note": "Escape on a Two Sides window leaves the sketch exactly as it was."},
+ {"start": "sketch.offset"},
+ {"click": {"sketch": [20, 0]}},
+ {"click": {"handle": "dialog:Direction:Two Sides"}},
+ {"expect": {"dialog": "Offset"}},
+ {"key": "Escape"},
+ {"expect": {"dialog": null, "errors": 0, "sketch_curves": {"own": 12}}}
+]