// swaps an edge (a.org, b.org) with (a.dst, b.dst)
void swap(edge er) {
Edge_Record a, b;
a = er.oprev();
b = er.sym().oprev();
splice(er, a);
splice(er.sym(), b);
splice(er, a.lnext());
splice(er.sym(), b.lnext());
er.get_qr().v = a.sym().get_qr().v;
er.sym().get_qr().v = b.sym().get_qr().v;
}
void delete_all_edges(edge hull_edge) {
edge e, e1, e2;
std::vector<Quadedge*> *to_delete = new std::vector<Quadedge*>;
// mark all hull edges as visited
e = hull_edge.sym();
while (not e.get_qr().flag) {
e.get_qr().flag = true; // visited
to_delete->push_back(e.q);
e = e.lnext();
}
// perform dfs and mark all visited faces
std::stack<edge> fringe = std::stack<edge>();
fringe.push(hull_edge);
// invariants:
// if e is popped, e's sym() was already visited
// if e is not visited, neither have any of the other edges of the face
while (not fringe.empty()) {
e = fringe.top();
fringe.pop();
if (not e.get_qr().flag) {
// visit the triangle left of e, mark e and all adjoining edges
// add the sym() of each visited edge except e
e1 = e.lnext();
e2 = e1.lnext();
// assert e == e2.lnext()
e.get_qr().flag = true;
if (not e.sym().get_qr().flag) {
to_delete->push_back(e.q);
}
e1.get_qr().flag = true;
if (not e1.sym().get_qr().flag) {
to_delete->push_back(e1.q);
fringe.push(e1.sym());
}
e2.get_qr().flag = true;
if (not e2.sym().get_qr().flag) {
to_delete->push_back(e2.q);
fringe.push(e2.sym());
}
}
}
std::vector<Quadedge*>::iterator it;
for (it = to_delete->begin(); it != to_delete->end(); ++it) {
delete *it;
}
delete to_delete;
}
// given a counterclockwise convex hull edge, returns a string of triangles
// <v1> <v2> <v3>
// oriented counter clockwise, separated by newlines
std::string serialize_triangles(edge hull_edge) {
edge e, e1, e2;
// mark all hull edges as visited (we don't return the open face)
e = hull_edge.sym();
while (not e.get_qr().flag) {
e.get_qr().flag = true; // visited
e = e.lnext();
}
// perform dfs and mark all visited faces
std::string output = "";
std::stack<edge> fringe = std::stack<edge>();
fringe.push(hull_edge);
// invariants:
// if e is popped, e's sym() was already visited
// if e is not visited, neither have any of the other edges of the face
while (not fringe.empty()) {
e = fringe.top();
fringe.pop();
if (not e.get_qr().flag) {
// visit the triangle left of e, mark e and all adjoining edges
// add the sym() of each visited edge except e
std::stringstream ss;
e1 = e.lnext();
e2 = e1.lnext();
// assert e == e2.lnext()
ss << e.org() << " ";
e.get_qr().flag = true;
ss << e1.org() << " ";
e1.get_qr().flag = true;
fringe.push(e1.sym());
ss << e2.org() << "\n";
e2.get_qr().flag = true;
fringe.push(e2.sym());
std::string triangle = ss.str();
output += triangle;
}
}
// unvisit the hull
e = hull_edge.sym();
while (e.get_qr().flag) {
e.get_qr().flag = false; // unvisit
e = e.lnext();
}
// perform dfs and unmark all visited faces
fringe.push(hull_edge);
// invariants:
// if e is popped, e's sym() was already unvisited
// if e is not visited, neither have any of the other edges of the face
while (not fringe.empty()) {
e = fringe.top();
fringe.pop();
if (e.get_qr().flag) {
// unvisit the triangle left of e, unmark e and all adjoining edges
// add the sym() of each unvisited edge except e
e1 = e.lnext();
e2 = e1.lnext();
// assert e == e2.lnext()
e.get_qr().flag = false;
e1.get_qr().flag = false;
fringe.push(e1.sym());
e2.get_qr().flag = false;
fringe.push(e2.sym());
}
}
return output;
}
// removes an edge er, deletes its corresponding quadedge.
void delete_edge(edge er) {
splice(er, er.oprev());
splice(er.sym(), er.sym().oprev());
delete er.q;
}
