Snap Interaction can snap to segments intersection

[langpavel]

I'm trying to snap to intersection point but also to edge too. Adding computed intersection point to Snap Interaction isn't working when edge snapping is enabled too (See #13440).

When I analyze the problem, I decided that computing intersection point in interaction itself can be the most efficient way.

[ahocevar]

I could think of adding an option for snapping to intersections. Optional because it would significantly increase the calculation time when the modification candidate geometries change. If you'd like to work on that, please feel free to create a pull request.