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Never allow degenerate faces to be created in smoothing 

Regardless of whether "safe moves only" is being used or not.

Degenerate faces are annoying because the normal is undefined (null_vector)
and then things get tricky.

The hope is that if a move would create a degenerate face, we can
just not move it, and hope that the degenerate face would not appear
on the next move.
This commit is contained in:
Mael Rouxel-Labbé 2020-02-05 18:07:21 +01:00
parent 238e18f002
commit a2bdfd57c9
1 changed files with 26 additions and 9 deletions
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35
Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Smoothing/mesh_smoothing_impl.h
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@ -544,12 +544,13 @@ public:
// Gram Schmidt so that the new location is on the tangent plane of v (i.e. do mv -= (mv*n)*n)
const FT sp = traits_.compute_scalar_product_3_object()(vn, move);
move = traits_.construct_sum_of_vectors_3_object()(move,
traits_.construct_scaled_vector_3_object()(vn, - sp));
move = traits_.construct_sum_of_vectors_3_object()(
move, traits_.construct_scaled_vector_3_object()(vn, - sp));
Point new_pos = pos + move;
if((!use_sanity_checks || !does_move_create_bad_faces(v, new_pos)) &&
const Point new_pos = pos + move;
if(move != CGAL::NULL_VECTOR &&
!does_move_create_degenerate_faces(v, new_pos) &&
(!use_sanity_checks || !does_move_create_bad_faces(v, new_pos)) &&
(!enforce_no_min_angle_regression || does_improve_min_angle_in_star(v, new_pos)))
{
#ifdef CGAL_PMP_SMOOTHING_DEBUG
@ -619,11 +620,10 @@ private:
return get(vcmap_, v);
}
// check for degenerate or inversed faces
bool does_move_create_bad_faces(const vertex_descriptor v,
const Point& new_pos) const
// Null faces are bad because they make normal computation difficult
bool does_move_create_degenerate_faces(const vertex_descriptor v,
const Point& new_pos) const
{
// check for null faces and face inversions
for(halfedge_descriptor main_he : halfedges_around_source(v, mesh_))
{
const halfedge_descriptor prev_he = prev(main_he, mesh_);
@ -632,6 +632,23 @@ private:
if(traits_.collinear_3_object()(lpt, rpt, new_pos))
return true;
}
return false;
}
// check for degenerate or inversed faces
bool does_move_create_bad_faces(const vertex_descriptor v,
const Point& new_pos) const
{
// check for face inversions
for(halfedge_descriptor main_he : halfedges_around_source(v, mesh_))
{
const halfedge_descriptor prev_he = prev(main_he, mesh_);
const Point_ref lpt = get(vpmap_, target(main_he, mesh_));
const Point_ref rpt = get(vpmap_, source(prev_he, mesh_));
CGAL_assertion(!traits_.collinear_3_object()(lpt, rpt, new_pos)); // checked above
const Point_ref old_pos = get(vpmap_, v);
Vector ov_1 = traits_.construct_vector_3_object()(old_pos, lpt);