delete obsolete func based on: https://github.com/libigl/libigl/issue…

[xarthurx]

…s/1783#issuecomment-845248820

Fixes #1783

#1783 (comment)

Checklist

• All changes meet libigl style-guidelines.
• Adds new .cpp file.
• Adds corresponding unit test.
• This is a minor change.

[alecjacobson]

Wow. I didn't even realize this old function was defined for integer coordinates. I'm guess it wasn't getting used much. For posterity, if anyone was using this function before. Perhaps like this:

std::vector<std::vector<unsigned int > >poly;
unsigned int xt,yt;
bool res = igl::point_in_poly(poly,xt,yt);

You could switch to calling igl::winding_number:

Eigen::MatrixXd V;
igl::list_to_matrix(poly,V);
Eigen::MatrixXi E(V.rows(),2);
for(int v = 0;v<V.rows();v++){ E.row(v) << v,(v+1)%V.rows(); }
bool res = std::abs(igl::winding_number(V,E,Eigen::RowVector2d(xt,yt))>0.5;

For most users, you'll already have your polygon in the V format. igl::winding_number can also process many query points (in parallel). In the future, it'd be nice to implement the fast variants of wn for point-in-poly queries.

In my experience, igl::winding_number will hold up pretty well w.r.t. floating point robustness, with the most obvious pitfall of the singularity for points directly on the polygon (or "too close" for good floating point math). For a robust query, probably CGAL is needed.