Thin Extrude: walls of a set thickness along sketch curves (#721) (#991)

Thin Extrude builds walls of a set thickness along sketch curves, open chains and closed loops, with the wall centred, inside, outside or on both sides at two thicknesses. Saved under format 20 (thin on an Extrude); an extrude without thin saves as before. Closes #721.

docs/book/src/guide/features.md

@@ -7,7 +7,7 @@ it.
 
 | Panel | Features |
 |---|---|
-| Create | extrude (one side, two sides, symmetric, taper, start offset, to a distance or through all; new body, join, cut, intersect), revolve, sweep, loft, box, cylinder, sphere, torus, coil, pipe, rib, web, emboss, hole (simple, counterbore, countersink, tapped; on faces or at sketch points), thread, rectangular/circular/path patterns, mirror |
+| Create | extrude (one side, two sides, symmetric, taper, start offset, to a distance or through all; new body, join, cut, intersect; thin walls along curves), revolve, sweep, loft, box, cylinder, sphere, torus, coil, pipe, rib, web, emboss, hole (simple, counterbore, countersink, tapped; on faces or at sketch points), thread, rectangular/circular/path patterns, mirror |
 | Modify | press pull, fillet, chamfer, shell, draft, scale, combine, split body, offset face, replace face, move/copy, align, remove |
 | Construct | offset plane, plane at angle, plane along path |
 | Inspect | measure, section analysis, interference, curvature comb and map, zebra, draft, minimum radius, isocurves, centre of mass |
@@ -23,6 +23,19 @@ curves move in or out together, and a flat tip shorter than the taper closes to
 taper steeper than the profile's details (a stroke, a curve or a gap narrower than it) is
 refused with that reason; a smaller taper or distance builds.
 
+**Thin Extrude** (`thin: true` on `solid.extrude`, the Thin Extrude box in its dialog) builds a
+wall of constant thickness along sketch curves instead of filling profiles: open chains (a single
+wall) and closed loops (a ring), lines, arcs, circles, ellipses and splines. In the dialog, a
+picked profile stands for the curves around it (its outline and its holes). The wall lies on the curves' centre, inside,
+outside, or on both sides with two thicknesses (`side`: `center`, `inside`, `outside`,
+`two_sides` with `thickness2`). A closed loop's inside is the area it encloses; an open chain's
+is the side it bends toward (the inside of a U), and a straight line's is the left of its first
+curve as drawn. Curves that meet end to end are one chain whose corners are mitred; walls that
+cross or meet (a ring and a cross, a honeycomb) become one piece. Every extent, operation and target of an extrude applies, and a taper
+for walls of straight lines or of whole circles. A wall thicker than the
+radius of a curve it follows on the inside is refused. Spline walls follow the exact offset
+within 0.0001 mm.
+
 Editing an extrusion retains its signed distances, From/To Object inputs, taper expressions
 and explicit body targets. Revolve edits retain world, sketch and explicit-line axes, both
 angle expressions and To Object targets. An unchanged **All profiles** selection continues
@@ -124,7 +137,7 @@ still be added through `set`. The fields of the common features:
 
 | Feature | Fields |
 |---|---|
-| Extrude | `extent`: {`distance`, `direction`: positive\|negative\|symmetric, `distance2`, `start_offset`, `through_all`, `taper`, `to`, `to_offset`, `from`}; `operation`: new_body\|join\|cut\|intersect; `targets`; `profiles`; `sketch` |
+| Extrude | `extent`: {`distance`, `direction`: positive\|negative\|symmetric, `distance2`, `start_offset`, `through_all`, `taper`, `to`, `to_offset`, `from`}; `operation`: new_body\|join\|cut\|intersect; `targets`; `profiles`; `sketch`; `thin`: {`curves`, `thickness`, `side`: center\|inside\|outside\|two_sides, `thickness2`} |
 | Revolve | `angle`, `angle2`, `symmetric`, `axis`, `to`, `operation`, `targets`, `profiles`, `sketch` |
 | Fillet | `radius`, `edges` (a point on each edge), `body`, `style` |
 | Chamfer | `distance`, `distance2` or `angle`, `flip`, `edges`, `body` |

docs/book/src/guide/files.md

@@ -73,7 +73,7 @@ is available. Missing or incompatible pictures use the usual thumbnail generatio
 The default `cache: false` omits the portable thumbnail too.
 The repository's `docs/design-container.md` describes limits and encoding details.
 
-Current designs use format 19, including editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
+Current designs use format 20, including thin extrudes, editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
 links, persistent
 names from exact face history, exact planar shell-face anchors, persistent analytic offset boundary roles and
 association profile references, durable sketch face anchors, periodic fit splines and versioned

docs/design-container.md

@@ -7,7 +7,7 @@ self-contained input/output format. `io::write_design` keeps its JSON contract;
 `io::write_design_container` is the fallible container writer.
 
 Packages have `container.json` with `{"format":"solidcraft-container/1"}` and
-`document.json` with the versioned parametric document (currently `solidcraft/19`).
+`document.json` with the versioned parametric document (currently `solidcraft/20`).
 The independent versions let document migrations evolve without changing blob encodings.
 Existing serialized document fields are retained automatically, without a second copy
 of the document schema or a deep clone of embedded payloads.

docs/oracle.md

@@ -9,7 +9,7 @@ Where the expected values come from (the **Source** column):
 
 No expected value comes from a commercial CAD product.
 
-**81 / 81 cases pass**; sources: 60 analytic, 21 freecad. 0 known failure(s) tracked in issues; 0 case(s) without expected values yet.
+**82 / 82 cases pass**; sources: 61 analytic, 21 freecad. 0 known failure(s) tracked in issues; 0 case(s) without expected values yet.
 
 | Case | Source | Result | Surface distance mm (max / mean) | Method | Notes |
 |---|---|---|---|---|---|
@@ -54,7 +54,7 @@ No expected value comes from a commercial CAD product.
 | 39-tee-pipe | freecad 1.1.4 | pass | 0.008 / 0.0014 (worst at -9.7, 2.4, 40.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part extrude join, Part extrude cut |  |
 | 40-box-sphere-torus | analytic | pass |  | box 60x60x10 (z -10..0) + upper hemisphere r12 + spherical cap h2 below z=-10 (V = pi h^2(3R-h)/3, A = 2 pi R h) - lower half torus R22 r4 (Pappus: V = pi r^2/2 * 2 pi R, centroid -4r/3pi, A = pi r * 2 pi R); top loses disc r12 and annulus 18..26, bottom loses disc r sqrt(44) | faces: bottom, 4 sides, top split by the groove into an annulus (r 12..18) and the outer part, upper sphere, lower cap, torus |
 | 41-tube-radial-holes | freecad 1.1.4 | pass | 0.010 / 0.0012 (worst at 1.9, 19.9, 24.8) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part extrude cut, pattern (tools transformed and re-applied) |  |
-| 42-overlapping-patterns | freecad 1.1.4 | pass | 0.030 / 0.0010 (worst at -20.0, -0.0, 5.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part extrude cut, pattern (tools transformed and re-applied), Part extrude cut, pattern (tools transformed and re-applied) |  |
+| 42-overlapping-patterns | freecad 1.1.4 | pass | 0.009 / 0.0010 (worst at -1.0, -10.1, 2.2) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part extrude cut, pattern (tools transformed and re-applied), Part extrude cut, pattern (tools transformed and re-applied) |  |
 | 43-cut-splits-body | analytic | pass |  | two boxes 35x20x20 (x 0..35 and 45..80): V = 2abc, A = 2*2(ab+bc+ca) |  |
 | 44-shell-l-bracket | analytic | pass |  | L prism (area 736, perimeter 200) x 20 minus cavity = L shrunk by 2 (SolidCraft's intersection-join shell convention: inner faces offset by 2 and extended to meet, sharp inner corner at (6,6); area 352) from z=2 to 20. A rounded (arc) join would give V 8368.5487, A 8768.5487, 16 faces |  |
 | 45-shell-boss-plate | analytic | pass |  | plate 60x60x10 + boss r12 h20 minus cavity (box 56x56x8 + cylinder r10 z8..28) under SolidCraft's intersection-join shell convention (offset faces extended to meet: sharp circular inner edge at r10, z8). A rounded (arc) join would give V 13620.2567, A 14104.4455, 16 faces (torus round r2) |  |
@@ -71,13 +71,13 @@ No expected value comes from a commercial CAD product.
 | 56-holes-on-curved-face | freecad 1.1.4 | pass | 0.009 / 0.0018 (worst at -16.9, 18.5, 0.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, hole tool (cylinder/cone) cut |  |
 | 57-hole-pattern-sketch-points | analytic | pass |  | plate 80x50x10 minus 6 counterbored through holes (cb d10 x 5.5, hole d5.5) at x 15/40/65, y 15/35 |  |
 | 58-phone-stand | freecad 1.1.4 | pass | 0.007 / 0.0010 (worst at 82.5, 11.7, 6.1) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part makeFillet, Part extrude cut |  |
-| 59-enclosure-base | freecad 1.1.4 | pass | 0.008 / 0.0017 (worst at 90.9, 51.0, 6.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part makeFillet, makeThickness shell, Part extrude join, Part extrude cut |  |
+| 59-enclosure-base | freecad 1.1.4 | pass | 0.008 / 0.0017 (worst at 90.9, 53.0, 6.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part makeFillet, makeThickness shell, Part extrude join, Part extrude cut |  |
 | 60-pipe-flange | freecad 1.1.4 | pass |  | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part revolve, Part extrude cut, pattern (tools transformed and re-applied), Part makeChamfer, Part makeFillet | No reference.stl: over 409600 bytes even at 0.02 mm deflection (11380 facets). |
-| 61-shaft-keyway | freecad 1.1.4 | pass | 0.008 / 0.0019 (worst at 11.9, 3.9, 45.8) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part revolve, Part makeChamfer, Part extrude cut |  |
+| 61-shaft-keyway | freecad 1.1.4 | pass | 0.008 / 0.0019 (worst at 12.2, 2.8, 72.1) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part revolve, Part makeChamfer, Part extrude cut |  |
 | 62-heat-sink | analytic | pass |  | base 60x50x5 + 15 fins 1.5x50x25 at x = 2 + 4k: sums of boxes; fin ends coplanar with the base ends | faces: bottom, x=0, x=60, y=0 and y=50 (each merged with the fin ends), 16 base-top strips, 15x3 fin faces |
 | 63-hinge-knuckle | freecad 1.1.4 | pass | 0.008 / 0.0016 (worst at 28.0, 36.9, 4.7) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Part extrude, Part extrude join, Part extrude cut |  |
 | 64-sketch-tangent-arc-chain | analytic | pass |  | solved sketch: 80x20 rectangle whose top is 4 tangent R12 arcs on 20 mm chords alternating up/down (net area 1600); prism h3: V = A h, area = 2A + perimeter*h, Green's theorem for centroid |  |
-| 65-sketch-gear-tooth | freecad 1.1.4 | pass | 0.008 / 0.0017 (worst at 6.5, 39.5, 8.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Sketcher-solved sketch, Part extrude |  |
+| 65-sketch-gear-tooth | freecad 1.1.4 | pass | 0.008 / 0.0017 (worst at -6.5, 39.5, 0.0) | FreeCAD (OpenCASCADE) build of recipe.json by tools/freecad-oracle/build.py: Sketcher-solved sketch, Part extrude |  |
 | 66-sketch-linkage | analytic | pass |  | solved sketch: hull of circles R12 at (0,0) and R8 at (60,0) (outer tangent lines, cos a = 4/60) minus holes d12, d8 (concentric) and d4 at (30,+-4) (symmetry keeps radii equal); prism h6 |  |
 | 67-sm-base-flange | analytic | pass |  | plate 100 x 60 x t, t = 2.5 (Steel (mm) rule), thickness along +Z: V = 100*60*t, A = 2(ab+bc+ca) |  |
 | 68-sm-edge-flange | analytic | pass |  | extrusion along x (100) of the YZ section: base y 5..60 x t; 90 deg bend annulus R 2.5..5 about (y 5, z 5); flange y 0..2.5, z 5..20. Setback (R+t)tan45 = 5 (inside bend position, outer-face height datum: outer face of flange reaches z = 20); V = L*A_sec, A = 2 A_sec + L P_sec | trim/setback and height datum are SolidCraft's documented edge-flange conventions (sheet.rs add_flanges) |
@@ -94,6 +94,7 @@ No expected value comes from a commercial CAD product.
 | 79-fillet-chord-length | analytic | pass |  | box 40x30x20, top front edge rounded 4 wide across (chord c): r = c / (2 cos 45 deg) = 2 sqrt 2; V = abc - (1 - pi/4) r^2 L, A = 2(ab + bc + ca) - 2 r L + (pi/2) r L - 2 (1 - pi/4) r^2 |  |
 | 80-fillet-taper-to-fit | analytic | pass |  | plate (top 20 -> 2 wide over x 0..40, 15 high) with its top front edge filleted at 3, fit: taper. The radius is the taper law: a clamped cubic B-spline in u = x/40 on 8 equal spans, control radii min(3, 0.9 room) at the Greville abscissae, room = min(20 - 18u, 15) tan 45 deg (top face width, front face height): 3.0000, 3.0000, 3.0000, 3.0000, 3.0000, 3.0000, 3.0000, 3.0000, 3.0000, 2.4750, 1.8000. Sections are quarter rounds; V, moments and areas integrated along the edge |  |
 | 81-fillet-spline-radius | analytic | pass |  | box 40x30x20 with its top front edge (y=0, z=20) rounded at a radius that is a clamped cubic B-spline in u = x/40, knots 0,0,0,0,0.25,0.6,1,1,1,1, control radii 2, 5, 1.5, 4, 1, 3 (r(0) = 2, r(40) = 3). Sections are quarter rounds; V, moments and areas integrated along the edge, exactly per knot span |  |
+| 82-thin-extrude-frame | analytic | pass |  | square frame: the lines' 40 mm square walled 3 mm inside and 1 mm outside (mitred corners) is 42 x 42 less 34 x 34, 10 mm tall: V = (42^2 - 34^2) * 10, A = 2 (42^2 - 34^2) + 4 * 42 * 10 + 4 * 34 * 10 |  |
 
 ## Not covered by a reference case