Module split 

Splitting a face along curves: edges lying on it, or dropped onto it along its normals or along a direction.

Each curve is first given its trace in the face’s chart: its own pcurve where it carries one on the surface, the exact or fitted one where it lies on the surface, or, for a projection, the curve through its landed points fitted together with their chart positions, so curve and trace share a parameter. A trace leaving the face’s window of a chart that wraps round (it repeats, or its two sides are one line of points) is cut there and brought back by a period, and the pieces of all the curves are chained end to end into paths.

Each path is then cut where it meets the face’s boundary, and each stretch of it inside the face divides the face it runs through: a stretch from one point of a boundary loop to another point of the same loop cuts that loop in two, and a path closing on itself inside the face cuts out the region it encloses, leaving a hole in the rest. A closed path that meets the boundary is walked from a meeting, so it is a stretch from the boundary to the boundary. Stretches are cut one at a time, so a later path meets the pieces of the earlier ones as boundary and may end on them.

The boundary edges a stretch ends on are cut there in every face that holds them, so the rest of the shape stays joined to the pieces. Pieces a piece of the face’s own seam parts are joined again into one face, whose boundary jumps a period where it crosses the seam.

Enums

Projection

How the curves to split along reach the face.

Functions

split_face

Cut face of shape along edges and rebuild shape around the pieces.