/**
* Try to flip a given edge, If successfull, return the new edge (reffed!),
* otherwise return NULL
*/
P2trEdge*
p2tr_cdt_try_flip (P2trCDT *self,
P2trEdge *to_flip)
{
/* C
* / | \
* B-----A to_flip: A->B
* \ | / to_flip.Tri: ABC
* D
*/
P2trPoint *A, *B, *C, *D;
P2trEdge *AB, *CA, *AD, *DB, *BC, *DC;
g_assert (! to_flip->constrained && ! to_flip->delaunay);
A = P2TR_EDGE_START (to_flip);
B = to_flip->end;
C = p2tr_triangle_get_opposite_point (to_flip->tri, to_flip, FALSE);
D = p2tr_triangle_get_opposite_point (to_flip->mirror->tri, to_flip->mirror, FALSE);
AB = to_flip;
/* Check if the quadriliteral ADBC is concave (because if it is, we
* can't flip the edge) */
if (p2tr_triangle_circumcircle_contains_point (AB->tri, &D->c) != P2TR_INCIRCLE_IN)
return NULL;
CA = p2tr_point_get_edge_to (C, A, FALSE);
AD = p2tr_point_get_edge_to (A, D, FALSE);
DB = p2tr_point_get_edge_to (D, B, FALSE);
BC = p2tr_point_get_edge_to (B, C, FALSE);
p2tr_edge_remove (AB);
DC = p2tr_mesh_new_edge (self->mesh, D, C, FALSE);
p2tr_triangle_unref (p2tr_mesh_new_triangle (self->mesh,
CA, AD, DC));
p2tr_triangle_unref (p2tr_mesh_new_triangle (self->mesh,
DB, BC, DC->mirror));
return DC;
}
/* Whenever a new point was inserted, it may disturb triangles
* that are extremly skinny and therefor their circumscribing
* circles are very large and will contain that point, even though they
* may be very far from that point.
* We have no choice but to check these and fix them if necessary
*/
static void
p2tr_cdt_on_new_point (P2trCDT *self,
P2trPoint *pt)
{
GList *bad_tris = NULL;
P2trTriangle *tri;
P2trHashSetIter iter;
p2tr_hash_set_iter_init (&iter, self->mesh->triangles);
while (p2tr_hash_set_iter_next (&iter, (gpointer*)&tri))
{
if (p2tr_triangle_circumcircle_contains_point (tri, &pt->c)
!= P2TR_INCIRCLE_OUT)
{
bad_tris = g_list_prepend (bad_tris, tri);
p2tr_triangle_ref (tri);
}
}
p2tr_cdt_flip_fix (self, bad_tris);
g_list_free (bad_tris);
}
