// This file is part of libigl, a simple c++ geometry processing library.
//
// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla Public License
// v. 2.0. If a copy of the MPL was not distributed with this file, You can
// obtain one at http://mozilla.org/MPL/2.0/.
#include "flipped_triangles_ids.h"

#include <igl/edge_topology.h>

template <typename Scalar, typename Index>
IGL_INLINE Eigen::VectorXi flipped_triangles_ids(
  const Eigen::PlainObjectBase<Scalar> & V,
  const Eigen::PlainObjectBase<Index> & F
)
{
  assert(V.cols() == 2);
  std::vector<int> flip_idx;
  for (int i = 0; i < F.rows(); i++) {

    Eigen::Vector2d v1_n = V.row(F(i,0)); Eigen::Vector2d v2_n = V.row(F(i,1)); Eigen::Vector2d v3_n = V.row(F(i,2));

    Eigen::MatrixXd T2_Homo(3,3);
    T2_Homo.col(0) << v1_n(0),v1_n(1),1;
    T2_Homo.col(1) << v2_n(0),v2_n(1),1;
    T2_Homo.col(2) << v3_n(0),v3_n(1),1;
    double det = T2_Homo.determinant();
    assert (det == det);
    if (det < 0) {
      flip_idx.push_back(i);
    }
  }

  Eigen::VectorXi ret(flip_idx.size());
  for (unsigned i=0; i<flip_idx.size();++i)
    ret[i] = flip_idx[i];

  return ret;
}

#ifdef IGL_STATIC_LIBRARY
// Explicit template specialization
// generated by autoexplicit.sh
#endif