Module boundary 

BoundarySurface: a face standing on its own, spanned by edges — the ruled face between two of them, or a closed loop of them filled.

Two edges that do not close a loop are joined by the ruled surface between them (see NurbSurface3D::ruled), the second turned, if need be, so that their ends line up, and a straight edge at either end.

A closed loop — the edges picked in any order, each running either way, end to end — is filled:

• flat, where every edge lies in one plane: one face on that plane, trimmed by the loop, exactly as an extrude’s cap is. Any number of edges, a single circle included.
• four edges: their Coons patch (see NurbSurface3D::coons), which runs exactly along every one of them. Along edges picked as tangent it is made tangent to the face each of those edges bounds, continuing it smoothly (see NurbSurface3D::tangent_to): exactly to a flat face, and to a curved one leaving it at a millionth of a radian outwards, proven so all along, so that it never dips through it.
• three, or five and more: a flat inner polygon and a quadrilateral along every edge, between the edge, the spokes from its ends to the inner polygon and the polygon’s side (see NurbSurface3D::fill). The fill runs exactly along the loop, every edge whole — it knits to the faces around the hole — and is smooth inside: the quadrilaterals meet each other across the spokes, and the polygon, tangentially. Along edges picked as tangent it is tangent to their faces, as a patch of four is.

A Coons patch needs a corner wherever two of its sides meet: a loop of four that runs on smoothly through a vertex leaves a patch with no normal there, and is refused, naming the vertex. Two edges sharing an end are ruled into a face that comes to a point there, as a cone into its apex: that side of the patch collapses to the shared vertex.

Structs

BoundarySurface

Spans a face standing on its own between the curves edges — two of them ruled, a closed loop of them filled, see the module docs — for the operation B. A curve is an edge, of a face or of a wire — a 3-D sketch’s line, arc or spline — or a planar sketch’s curve. The curves are copied, the originals left as they are; with tangent, the fill continues the faces those of its edges bound smoothly.

BoundarySurfaceArgs

Functions

boundary_surface

The sheet spanned between edges, tangent along tangent (see the module docs), each a curve picked, the edges of tangent by name, in part: what to build, named after namer, as BoundarySurface says.