Module out_and_back 

Where a face’s boundary runs out along a path and straight back along it.

Two consecutive edges of a wire, the first from one vertex to another and the second from that one back along the first, bound nothing between them: the region the wire encloses is the same with that stretch of boundary as without. The tip is a vertex of the boundary that bounds no corner, every boolean through the face meets a strand there, and a mesher has to strip it before it can triangulate.

• A tail: the second edge comes back to the vertex the first left from. Both edges run out and back whole. is_tail also takes one edge walked out and straight back (a slit), which the booleans cut and make with exact volumes; out_and_back does not report a slit, only two distinct edges over one path.
• A notch: one edge runs farther than the other. The shorter one’s far end stands on the longer within the tolerance either edge or that vertex states, and the stretch of the longer from there to the tip runs along the shorter. Only that stretch and the shorter edge bound nothing.

A pair is one only where all of these hold, so that nothing a neighbour holds or the chart tells apart is taken for one:

• neither edge is degenerate, and the pair’s ends are distinct vertices;
• no other face of the shape walks either edge, nor this face again, except as the pair itself (one edge walked out and back, a tail). Uses are counted per placed occurrence: two placements of one face share every node, but each walks its own edges;
• neither edge is a seam on the face, and in the face’s chart the tip is one point, and a tail’s walk back ends where its walk out began, with no whole period between them along a direction the surface closes in: two meridians a period apart on a sphere are one curve in space and bound the whole sphere between them in the chart;
• the two curves stand no farther apart than the wider of the two edges’ tolerances anywhere along the stretch that runs out and back.

Structs

Notch

Where a notch’s shorter edge turns back from the longer.

OutAndBack

Two consecutive edges of a face’s wire running out and back along one path. See the module documentation.

Functions

edge_uses

How many times each edge node is walked by the faces of shape, every placed occurrence of it together.

is_tail

Whether out, then back, walked in that order by one wire of the face on surface, are a tail. uses counts how many times the faces of the shape walk each edge as placed (placed_edge_uses). See the module documentation.

notch_of

The notch out, then back, walked in that order by one wire of the face on surface, make, where they make one. See is_tail and the module documentation.

out_and_back

Every pair of consecutive edges of a face of shape that runs out and back along one path, tails of two distinct edges and notches alike, face by face in the shape’s order and wire by wire; a slit, one edge walked out and back, is not one. See the module documentation.

placed_edge_uses

How many times each edge of shape, as placed (node and placement, SameKey), is walked by the faces of shape.