This patch adds support for clip_planes (ie ignore what is behind a face)... The idea is to first execute a raycast to get the polygon to which the mouse cursor points. Then a snap test is done on the vertices or edges of the polygon. Then with the normal and location obtained in raycast a new clip_plane is created and the snap over the whole scene is processed ignoring the elements behind the clip_plane. Here 2 gif of how the previous patch would work on blender2.79: {F497176} {F497177} Reviewers: mont29, campbellbarton Reviewed By: campbellbarton Subscribers: bliblubli Tags: #bf_blender_2.8 Differential Revision: https://developer.blender.org/D2527