[Basnederveen]

What

New curve and surface family: geometry given in a flat space and bent around a cylinder axis, the way a sheet metal bend wraps a flat sheet.

Wrap { frame, radius } maps a flat point (x, y, z) to frame.point([z cos(x/r), z sin(x/r), y]). x is arc length on radius r, y runs along the axis, z is the distance from the axis, so lines along flat z become radial lines. The map is exact and preserves orientation (Jacobian determinant z / r).

• CurveGeometry::Wrapped { wrap, curve } wraps a line, circle or ellipse.
• SurfaceGeometry::Wrapped { wrap, surface } wraps any elementary surface.

Both keep the flat geometry's parameters and charts, so pcurves are written in the flat surface's UV.

Why: a cut through a bend has no analytic support. A round hole through a bend has a wrapped cylinder as its wall and wrapped circles as its edges. A slanted cut is a wrapped plane bounded by helices (wrapped lines). With this family such parts are exact B-reps rather than approximations.

Support across the kernel:

• Geometry: point, first and second derivatives (chain rule through the wrap), normal (cofactor of the Jacobian), projection (exact on the surface; the angle is taken in (-pi, pi] around frame.x unless a hint picks the turn), and conservative interval bounds for curves and surfaces.
• Tessellation:
  • Grid sizes come from the exact second derivatives, sampled on a 9 x 9 grid of the patch with a 1.5x margin. A strict closed-form bound is far too loose along the rulings.
  • Periodic parameters keep the existing turn floor.
  • Wrapped circles and ellipses get the same per-turn floor as circles.
  • The area error bound reports infinity for wrapped faces (no closed-form bound yet).
• Point classification: ray roots on a wrapped face come from UV subdivision while the face's conservative box meets the ray, then Newton from each small box. There is no implicit form.
• STEP export:
  • Wrapped surfaces become bicubic B_SPLINE_SURFACE_WITH_KNOTS over the UV of all faces on that support. The knots are the surface's own parameters, so pcurves stay valid.
  • Wrapped edges become cubic B_SPLINE_CURVE_WITH_KNOTS over every range an edge uses.
  • Both are Hermite fits, checked against the exact geometry at 16 samples per span or patch side, and their error is charged to the exchange budget.
• Placement: rigid moves only. Scaling wrapped geometry is refused.
• Refused with UnsupportedGeometry: booleans, shells, SSI, mirroring and IFC export of wrapped geometry.

Compatibility:

• JSON gains a "kind": "Wrapped" for curves and surfaces, and existing bodies read unchanged.
• In Rust, CurveGeometry and SurfaceGeometry gain a variant, so an exhaustive match over them in downstream code needs a new arm. Two integration tests in this repo did (tests/primitives.rs, tests/creating/sweep_bends.rs).
• Nothing changes on the TypeScript side.

Robustness

• A fitted surface reaches 10% past its faces in each direction, but never around a periodic direction onto itself (a hole wall spans a full turn). Some CAD readers rebuild a face's trim by intersecting its neighbouring surfaces and ignore the pcurves. A B-spline that ends exactly on the face's edges makes such a reader trim short, by up to the fit error.
• A wrapped surface cannot wrap another wrapped surface. A wrapped curve must wrap a line, circle or ellipse.
• The normal is refused (SingularParameterization) on the axis, where z <= 0.
• Ray classification gives up with Unknown after 50,000 boxes rather than guessing.
• The fitters stop at a span or patch budget with LimitExceeded, and STEP refuses when the exchange budget leaves no room for fitting.

Tests

• Per-family geometry tests: two wrapped surfaces join the existing family list (a hole wall through a bend, a slanted cut), covering derivatives, normals, projection and conservative boxes. A new test checks that the wrap keeps arc length on its radius, round-trips through flatten, and that a wrapped line is a constant-speed helix with a correct tangent and box. Another checks that wrapped circle samples meet their chord error.
• Fitting: a wrapped plane and a wrapped circle fit within tolerance between their samples.
• A bend sector with a slanted wrapped side (a builder fixture, 6 faces):
  • its mesh volume matches the exact volume (flat area times the radial integral of z / r) to 1e-4;
  • points on either side of the wrapped wall classify Inside and Outside;
  • it exports to STEP with one B-spline surface, two B-spline curves and a pcurve per edge use, within the exchange budget;
  • it moves rigidly, and refuses scaling, mirroring, booleans and shelling.
• On Windows with CI=true: cargo fmt --check, cargo clippy --all-targets -D warnings (kernel and test-support) and cargo test --all-targets pass, including the source_rules binary. That's 382 crate tests here, against 373 on main. npm run check:source, check:duplicates and check:cycles pass. Browser runs and the golden comparison were not run, because golden files are only recorded on macOS.

Files

• New:
  • src/brep/geometry/wrap.rs
  • src/query/wrapped_roots.rs
  • src/tessellation/wrapped.rs
  • src/exchange/fit_bezier/
  • src/exchange/step/wrapped.rs
  • src/brep/builder/fixtures.rs (test only)
• Variant arms: brep/geometry/{curve,surface,store,turned}.rs, brep/placement/, query/{classify,ray_roots}.rs, tessellation/{area_bound,deviation,grid,trim}.rs, intersection/ssi/, intersection/universal_ssi/implicit_bounds.rs, operations/modifying/boolean/{dispatch,batch,shell,handlers/sphere_sphere}, exchange/{preflight,step,ifc_body}.
• lift moved from surface.rs to turned.rs, so wrap.rs can share it without a sibling import cycle.
• tests/primitives.rs, tests/creating/sweep_bends.rs: a "wrapped" arm in their surface-kind helpers.

🤖 Generated with Claude Code

[Basnederveen]

Heads-up for merging this together with #37: there's no textual conflict, but the build fails once both are in. #37 adds raisable() in tessellation/loop_minimum.rs, which matches on CurveGeometry without the Wrapped variant from this PR:

error[E0004]: non-exhaustive patterns: `CurveGeometry::Wrapped { .. }` not covered
  --> src\tessellation\loop_minimum.rs:54:11

A wrapped curve is curved in 3D, so it should be raised in a non-planar loop just like an intersection curve:

CurveGeometry::Intersection { .. } | CurveGeometry::Wrapped { .. } => !planar,

With that one line, all seven open PRs (#35–#41) merged together pass fmt, clippy, the full test suite, check:source, check:duplicates and check:cycles.

I also pushed 8a22f57 to this PR. It puts the unsupported_wrapped import in boolean/shell.rs on its own line, so the file stays at 600 lines when #40's one-line addition lands next to it.