{

// Mesh with per-face color

Eigen::MatrixXd V, C;

Eigen::MatrixXi F;

// Load a mesh in OFF format

igl::readOFF(TUTORIAL_SHARED_PATH "/fertility.off", V, F);

// Initialize white

C = Eigen::MatrixXd::Constant(F.rows(),3,1);

igl::opengl::glfw::Viewer viewer;

viewer.callback_mouse_down =

[&V,&F,&C](igl::opengl::glfw::Viewer& viewer, int, int)->bool

{

int fid;

Eigen::Vector3f bc;

// Cast a ray in the view direction starting from the mouse position

double x = viewer.current_mouse_x;

double y = viewer.core().viewport(3) - viewer.current_mouse_y;

if(igl::unproject_onto_mesh(Eigen::Vector2f(x,y), viewer.core().view,

viewer.core().proj, viewer.core().viewport, V, F, fid, bc))

{

// paint hit red

C.row(fid)<<1,0,0;

viewer.data().set_colors(C);

return true;

}

return false;

};

std::cout<<R"(Usage:

)";

// Show mesh

viewer.data().set_mesh(V, F);

viewer.data().set_colors(C);

viewer.data().show_lines = false;

viewer.launch();