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EngrCAD

Offset & Minkowski sums

Offset(distance) grows (or shrinks, when negative) the solid by a uniform distance — offsetting a box rounds its edges and corners exactly:

var scene = new Scene();
scene.Add(new Part("box", Shape.Box(24, 24, 24), Palette.Steel,
    Matrix4d.CreateTranslation((-30, 0, 17))));
scene.Add(new Part("offset +5", Shape.Box(24, 24, 24).Offset(5), Palette.Coral,
    Matrix4d.CreateTranslation((30, 0, 17))));

A box next to its outward offset with rounded edges

Minkowski sums (what OpenSCAD’s minkowski() is for)

OpenSCAD models rounding as minkowski() { part(); sphere(r); } — the Minkowski sum with a ball. That exact operation is Offset(r): for any solid, the sum with a ball of radius r is the set of points within r of it, which is precisely what the signed distance field’s offset computes — same geometry, evaluated in microseconds instead of OpenSCAD’s notoriously expensive convolution. The common recipes map directly:

OpenSCADEngrCADNotes
minkowski { part; sphere(r) }part.Offset(r)exact as a field; polygonized on the way to a mesh
erode then dilate (opening)part.Offset(-r).Offset(r)rounds convex edges, preserves size
dilate then erode (closing)part.Offset(r).Offset(-r)rounds concave corners
rounding a convex polyhedronpart.RoundEdges(r)exact B-Rep — the morphological opening as real planes, cylindrical bands and spherical corner patches, no field involved
rounding one rimpart.Fillet(r, faces)exact B-Rep rim surgery
minkowski with a cube—axis-aligned box dilation ≈ Offset under the Chebyshev metric; not provided — see below

For rounding, prefer the B-Rep routes (RoundEdges, Fillet, Chamfer) when they apply: they produce exact analytic surfaces that export to STEP and measure exactly, where the offset field polygonizes. Use Offset when the shape lives in field land anyway (blends, lattices, imported meshes) or when the B-Rep route refuses.

General minkowski() — an arbitrary solid swept by an arbitrary solid — is deliberately not planned. The ball case covers rounding, which is nearly every real use; the general polyhedron⊕polyhedron sum is a different algorithm entirely (convex decomposition of both operands, pairwise convex sums, then a union of the pieces — combinatorially explosive for non-convex parts, which is exactly why OpenSCAD’s is slow), and its engineering uses (tolerance zones, cam envelopes, clearance sweeps) are better served by Offset on the exact field of the real geometry. If you truly need a convex⊕convex sum, Shape.Hull of translated copies gives it: Hull(a.Translate(v₀), a.Translate(v₁), …) over b’s vertices vᵢ is exact for convex polyhedral a and b.