S2CopyingEdgeCrosser is exactly like S2EdgeCrosser, except that it makes its own copy of all arguments so that they do not need to persist between calls. This is less efficient, but makes it possible to use points that are generated on demand and cannot conveniently be stored by the client.
This class allows edges to be efficiently tested for intersection with a given fixed edge AB. It is especially efficient when testing for intersection with an edge chain connecting vertices v0, v1, v2, ...