Getting right-click position.

If a user selects a mesh, I want to be able to find the location of the right-click that he used.

Is this possible?

For example, if a mesh comprises 4 vertices, I want to know which of the 4 is closest to the point he clicked when he selected the mesh.


I guess if I could find the location of the mouse on the screen, if would help. Then I need to transcribe the mesh vertices to the screen and find which one is closest.