size_t carve::triangulate::detail::removeDegeneracies(vertex_info *&begin, std::vector<carve::triangulate::tri_idx> &result) {
vertex_info *v;
vertex_info *n;
size_t count = 0;
size_t remain = 0;
v = begin;
do {
v = v->next;
++remain;
} while (v != begin);
v = begin;
do {
if (remain < 4) break;
bool remove = false;
if (v->p == v->next->p) {
remove = true;
} else if (v->p == v->next->next->p) {
if (v->next->p == v->next->next->next->p) {
// a 'z' in the loop: z (a) b a b c -> remove a-b-a -> z (a) a b c -> remove a-a-b (next loop) -> z a b c
// z --(a)-- b
// /
// /
// a -- b -- d
remove = true;
} else {
// a 'shard' in the loop: z (a) b a c d -> remove a-b-a -> z (a) a b c d -> remove a-a-b (next loop) -> z a b c d
// z --(a)-- b
// /
// /
// a -- c -- d
// n.b. can only do this if the shard is pointing out of the polygon. i.e. b is outside z-a-c
remove = !internalToAngle(v->next->next->next, v, v->prev, v->next->p);
}
}
if (remove) {
result.push_back(carve::triangulate::tri_idx(v->idx, v->next->idx, v->next->next->idx));
n = v->next;
if (n == begin) begin = n->next;
n->remove();
count++;
remain--;
delete n;
} else {
v = v->next;
}
} while (v != begin);
return count;
}
/**
* \brief Determine whether p is internal to the anticlockwise
* angle ac, with apex at (0,0).
*
* @param[in] a
* @param[in] c
* @param[in] p
*
* @return true, if p is contained in a0c.
*/
inline bool internalToAngle(const P2 &a,
const P2 &c,
const P2 &p) {
return internalToAngle(a, P2::ZERO(), c, p);
}
