This snippet deals with selecting front facing polygons, thanks to paleajed for the hint on the eye code, and vrav for the suggestion to multiply obj_matrix with the face normal (turns out my demo object suzanne gets rotated around the x axis after insertion into the scene)
Paper on Visibility in Computer Graphics by Jirˇ´ı Bittner and Peter Wonka . This paper looks promising and might pave the way to get a decent faux3d svg render of 3d geometry.
