Extrude: a side drawn in collinear pieces is one face (#1788) (#1949)

Thanks @DuBearte.

crates/kernel/src/build.rs

@@ -190,6 +190,19 @@ pub(crate) fn frame_ok(plane: &Plane) -> bool {
 
 /// Extrude each region from `start` to `end` along the plane normal (offsets in mm, `end > start`).
 pub fn extrude(plane: &Plane, regions: &[Region2], start: f64, end: f64) -> Result<Vec<Body>> {
+    extrude_with(plane, regions, start, end, false)
+}
+
+/// [`extrude`] with each run of profile lines that continue one another in a straight line (a side
+/// drawn in two pieces, a mirrored half meeting its mirror image) swept into one side face over
+/// all its pieces, rather than coplanar faces with an edge between them (#1788). The side's
+/// history lists every piece under it. For the Extrude feature; other builders (sheet metal's
+/// flat pattern, tools) keep a face per segment.
+pub fn extrude_whole_sides(plane: &Plane, regions: &[Region2], start: f64, end: f64) -> Result<Vec<Body>> {
+    extrude_with(plane, regions, start, end, true)
+}
+
+fn extrude_with(plane: &Plane, regions: &[Region2], start: f64, end: f64, whole_sides: bool) -> Result<Vec<Body>> {
     if !frame_ok(plane) {
         return Err(KernelError::Invalid("extrude frame is not finite and orthonormal".into()));
     }
@@ -206,7 +219,19 @@ pub fn extrude(plane: &Plane, regions: &[Region2], start: f64, end: f64) -> Resu
     for r in regions {
         region_ok(r)?;
         let base = plane.offset(lo);
-        let profile = region_wires(&base, &oriented(r)?)?;
+        let pieces = oriented(r)?;
+        let numbered = if whole_sides { pieces.map_loops(|l| l.merged_lines(continues_straight)) } else { pieces.clone() };
+        // A joined side's source is its first piece, a segment of the profile as drawn (the side
+        // lies along it): the sketch curve it is certified and named by, as when it stood alone.
+        let first_piece = |side: &ProfileEdge| {
+            pieces
+                .loops()
+                .flat_map(|l| l.lp.segs.iter())
+                .copied()
+                .find(|piece| side.numbers.len() > 1 && piece.start() == side.segment.start())
+                .unwrap_or(side.segment)
+        };
+        let profile = region_wires(&base, &numbered)?;
         let wires = wires_of(&profile);
         let f = guard("extrude profile", || builder::try_attach_plane(&wires).map_err(|e| KernelError::Invalid(format!("profile: {e}"))))?;
         let solid: Solid = guard("extrude", || Ok(builder::tsweep(&f, v3(n * (hi - lo)))))?;
@@ -263,7 +288,7 @@ pub fn extrude(plane: &Plane, regions: &[Region2], start: f64, end: f64) -> Resu
                         _ => None,
                     };
                     (
-                        Some(crate::FaceSource::ExtrudeSide { segment: side.segment, plane: basis, coalesced: false }),
+                        Some(crate::FaceSource::ExtrudeSide { segment: first_piece(side), plane: basis, coalesced: false }),
                         Some(record::profile(&side.numbers)),
                     )
                 } else if Some(*id) == end {
@@ -285,6 +310,14 @@ pub fn extrude(plane: &Plane, regions: &[Region2], start: f64, end: f64) -> Resu
     Ok(out)
 }
 
+/// `t` carries on from `s` in the same straight line: the turn at their meeting point is within
+/// rounding of none, measured against both lengths.
+fn continues_straight(s: &Seg2, t: &Seg2) -> bool {
+    let (u, v) = (s.end() - s.start(), t.end() - t.start());
+    let (lu, lv) = (u.len(), v.len());
+    lu > 0.0 && lv > 0.0 && s.end().dist(t.start()) <= 1e-9 * (lu + lv) && u.dot(v) > 0.0 && u.cross(v).abs() <= 1e-9 * lu * lv
+}
+
 /// Choose the per-profile axis sign whose positive rotation follows the sketch normal.
 pub fn canonical_revolve_axis(plane: &Plane, region: &Region2, axis_origin: Vec2, axis_dir: Vec2) -> Result<Vec3> {
     if !axis_origin.is_finite() || !axis_dir.is_finite() || !plane.origin.is_finite() || !plane.x.is_finite() || !plane.y.is_finite() {

crates/kernel/src/history_tests.rs

@@ -244,3 +244,36 @@ fn face_sources_follow_kept_split_and_agreeing_merged_faces() {
     let s = h.face_sources(&[&a]);
     assert_eq!(s, vec![src(0), src(1), None, src(2), None]);
 }
+
+/// A side drawn in two collinear pieces (here the bottom edge, split at x = 10) sweeps into one
+/// side face over both pieces, not two coplanar faces with an edge between them (#1788).
+#[test]
+fn collinear_profile_lines_extrude_into_one_side_face() {
+    use solidcraft_geom::{Loop2, Plane, Region2, Vec2};
+    let pts = [(0.0, 0.0), (10.0, 0.0), (20.0, 0.0), (20.0, 10.0), (0.0, 10.0)].map(|(x, y)| Vec2::new(x, y));
+    let region = Region2 { outer: Loop2::polygon(&pts), holes: vec![] };
+    // Plain `extrude` keeps a face per segment (sheet metal's flat pattern relies on it).
+    assert_eq!(crate::extrude(&Plane::XY, std::slice::from_ref(&region), 0.0, 5.0).unwrap()[0].face_count(), 7);
+    let body = crate::extrude_whole_sides(&Plane::XY, &[region], 0.0, 5.0).unwrap().pop().unwrap();
+    assert_eq!(body.face_count(), 6, "a box has six faces");
+    assert!((crate::measure(&body).unwrap().volume - 1000.0).abs() < 1e-9);
+    let h = body.history().unwrap();
+    h.check(&body, &[]).unwrap();
+    let mut sides: Vec<Vec<FaceOrigin>> =
+        h.faces.iter().map(|f| f.origins.clone()).filter(|o| matches!(o.first(), Some(FaceOrigin::Profile { .. }))).collect();
+    sides.sort();
+    assert_eq!(
+        sides,
+        vec![
+            vec![FaceOrigin::Profile { segment: 0 }, FaceOrigin::Profile { segment: 1 }],
+            vec![FaceOrigin::Profile { segment: 2 }],
+            vec![FaceOrigin::Profile { segment: 3 }],
+            vec![FaceOrigin::Profile { segment: 4 }],
+        ],
+        "the bottom side is generated by both its pieces"
+    );
+    // A corner is not a straight run: an L-shaped step keeps its faces.
+    let step = [(0.0, 0.0), (10.0, 0.0), (10.0, 5.0), (20.0, 5.0), (20.0, 10.0), (0.0, 10.0)].map(|(x, y)| Vec2::new(x, y));
+    let body = crate::extrude_whole_sides(&Plane::XY, &[Region2 { outer: Loop2::polygon(&step), holes: vec![] }], 0.0, 5.0).unwrap().pop().unwrap();
+    assert_eq!(body.face_count(), 8);
+}

crates/kernel/src/lib.rs

@@ -151,8 +151,8 @@ pub use boundary::{Boundary, boundary_patch};
 pub use boundary_network::{BoundaryCurve, CurveSource, MAX_CHAIN_CURVES, MAX_EDGE_PICKS, boundary_join, boundary_surface};
 pub use bridge::{Continuity, Frame, blend_between, bridge, chain, chain_closes, frames, frames_across, sample_grid};
 pub use build::{
-    PathSeg, box_solid, canonical_revolve_axis, cylinder, extrude, extrude_tapered, extrude_tapered_between, loft, path_polyline, revolve,
-    revolve_whole, sphere, sweep, sweep_with, torus,
+    PathSeg, box_solid, canonical_revolve_axis, cylinder, extrude, extrude_tapered, extrude_tapered_between, extrude_whole_sides, loft,
+    path_polyline, revolve, revolve_whole, sphere, sweep, sweep_with, torus,
 };
 pub use clearance::{Clearance, Occupancy};
 pub use coaxial_overlap::{CoaxialOverlap, coaxial_overlap};