Module band 

Chains of curves in a plane, offset sideways — and the band between two offsets of one chain, the profile a rib or a lip is swept from.

Offsetting. A line moves sideways, an arc grows or shrinks around its centre: both stay exactly what they were. The offset of any other curve is no NURBS: a cubic is fitted through points of it, as many as it takes to come within [FIT_TOLERANCE] of the distance everywhere, proven (NurbCurve2D::offset_miss). Where two pieces meet smoothly their offsets meet at the joint moved along its normal; where two lines meet at a corner their offsets are cut back, or run on, to where they cross — a mitre. A corner involving any other piece is not supported: its offsets would need a round of their own, or a cut at an angle no piece defines.

Structs

Chain

A chain of pieces, each starting where the one before ends — closed if the last ends where the first starts — and the names of its joints: joints[i] where piece i starts, and for an open chain one more, its end.

Piece

A curve of a chain, from where the previous one ends, named for what it was made from.