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Tommaso BianchiandClaude Opus 5
799f840218
snaporca-wm4s. Thickening the 4-walled open box (60x60 in plan, 40 tall, no caps) by 5 produced volume 29648.15 where the geometry requires (60^2-50^2)*40 = 44000 — about 67% of it. The corner material at the four vertical edges was simply absent. CAUSE. MakeThickSolidBySimple offsets each face along its own normal and sews; it never extends neighbours to meet, so wherever two faces join at an angle the corner is empty. A flat sheet has no such join and was always exact (18000.000), which is why the defect looked like a measurement artefact. WHY THE TWO EARLIER ATTEMPTS COULD NOT HAVE WORKED. Both switched to ByJoin — plain, then with Intersection/GeomAbs_Intersection — and both returned a shell, not a solid, so the body lost its volume entirely and both were reverted. That is not a parameter problem: in OCCT, BRepOffset_MakeOffset::MakeThickSolid builds a solid only inside `if (!myFaces.IsEmpty())` (BRepOffset_MakeOffset.cxx:1115). Handed an open sheet with no closing faces, it stops after the offset shell and returns it, reporting IsDone() with a non-null shape containing no TopAbs_SOLID. ByJoin hollows a CLOSED solid by removing faces; an open sheet is outside its contract. FIX. Close the sheet, then use the call that mitres: cap the free rims (ShapeAnalysis_FreeBounds -> MakeFace), sew shell+caps into a closed shell, make a solid, and hollow it inward passing the caps as the faces to remove — the caps come back off and leave the wall. Two details, each found by measurement rather than reasoning: * A shell sewn from an extruded sheet carries no guarantee of outward orientation, and MakeSolid does not fix it. Inside-out, the inward offset goes OUTWARD: measured bbox 70x70x40 and volume 339141.59, larger than its own bounding box because the result overlaps itself. A negative GProp mass is exactly that inversion, so it is the test; Reverse() on it. * A SINGLE face has no neighbour to mitre and must keep the BySimple path. It does have a free boundary, so "has free wires" is the wrong question — capping a lone face with its own rim sews a zero-thickness shell and measures 6000 against 18000. Also: IsDone() is not a success test here, since both failed attempts had it true. The code now explores for TopAbs_SOLID and refuses a shell. Tests: new case asserts 44000 with the wall's bbox at 60x60x40 (catching the inverted-orientation shape, which has the right volume nowhere near the right place), plus the flat-sheet control at 18000 that must not regress. Full kernel suite green: 2502 assertions in 187 test cases. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>