Posted by Rallaz on Mar 07, 2012; 4:23pm
URL: https://forum.librecad.org/Add-entities-beeing-created-to-main-container-tp5539557p5544633.html

It may be a nonsense but...

A snapPerpendicular is a point from "relative zero" to entity in mouse.

line by 2 points case with a snapPerpendicular activated
click the first point, the relative zero are moved to the clicked point,
click the second point, RS_Snapper::snapPoint is called
snapPoint gets the "relative zero" coordinate and calculate the
perpendicular point in the entity over the mouse