Derive a per-subpath anchor model from a PolygonPath. Subpaths split on
every M command; a subpath is closed iff it ends with Z.
Cubic-segment control points become the outHandle of the previous anchor
and the inHandle of the next anchor. Quadratic segments are upgraded to
cubics (each control reused for both adjacent handles) — this loses no
geometry. Linear segments produce anchors with no handles.
Derive a per-subpath anchor model from a PolygonPath. Subpaths split on every
Mcommand; a subpath is closed iff it ends withZ.Cubic-segment control points become the outHandle of the previous anchor and the inHandle of the next anchor. Quadratic segments are upgraded to cubics (each control reused for both adjacent handles) — this loses no geometry. Linear segments produce anchors with no handles.