void Mesh::computeFaceGradients(Eigen::MatrixXd& gradients, const Eigen::VectorXd& u) const
{
for (FaceCIter f = faces.begin(); f != faces.end(); f++) {
Eigen::Vector3d gradient;
gradient.setZero();
Eigen::Vector3d normal = f->normal();
normal.normalize();
HalfEdgeCIter he = f->he;
do {
double ui = u(he->next->next->vertex->index);
Eigen::Vector3d ei = he->next->vertex->position - he->vertex->position;
gradient += ui * normal.cross(ei);
he = he->next;
} while (he != f->he);
gradient /= (2.0 * f->area());
gradient.normalize();
gradients.row(f->index) = -gradient;
}
}
double Mesh::area( void ) const
{
double sum = 0.0;
for( FaceCIter f = faces.begin();
f != faces.end();
f ++ )
{
sum += f->area();
}
return sum;
}
