太可爱了，应该是insideTriangle问题，
auto times_0 = (px – _v[0]).cross(_v[1] – _v[0]);
auto times_1 = (px – _v[1]).cross(_v[2] – _v[1]);
auto times_2 = (px – _v[2]).cross(_v[0] – _v[2]);

试试这个