inline Bedge_list
quad_cell_end_edges(PCell* cell)
{
// if the cell is a quad (4 sides) and has one neigbhor,
// return the side opposite from the neighbor.
assert(cell && cell->num_corners() == 4);
PCell_list nbrs = cell->nbrs();
if (nbrs.size() != 1) {
err_adv(debug, "quad_cell_end_edges: neighbors: %d != 1", nbrs.size());
return Bedge_list();
}
// find an edge of the shared boundary.
// do it now before messing with flags...
assert(!cell->shared_boundary(nbrs[0]).empty());
Bedge* e = cell->shared_boundary(nbrs[0]).front();
assert(e);
EdgeStrip boundary = cell->get_boundary();
assert(boundary.num_line_strips() == 1);
// iterate around the boundary, setting edge flags to value
// k that is incremented whenever we pass a cell corner.
int k = 0;
PCellCornerVertFilter filter;
for (int i=0; i<boundary.num(); i++) {
if (filter.accept(boundary.vert(i)))
k = (k + 1)%4;
boundary.edge(i)->set_flag(k);
}
// we want the edges with flag == k + 2 mod 4
return boundary.edges().filter(
SimplexFlagFilter((e->flag() + 2)%4)
);
}
