Can I "lock" movement of a vertex to certain angles? In many 2d art programs, the user can draw lines that are "locked" to certain angles, e.g. in MS Paint holding SHIFT draws only 45 or 90 degree lines.

Is there a similar function in Blender, so that I can move vertices on 45 degree lines?

I know how to move vertices so that they stay on an axis, but I want to be able to constrain the vertices to a line 45 degrees between two axes.
Constrain to Custom Transform Orientation

I usually create a simple object (e.g an empty, or a cube...), rotate its local axis and create a Custom Transform Orientation from it (Ctrl+Alt+Space).


  Custom transform orientations defined from objects use the local orientation of the object whereas those defined from selected mesh elements (vertices, edges, faces) use the normal orientation of the selection.




Once created, the orientation can be selected in the Transform Orientation menù and called with doublepressing the axis shortcut (e.g. GXX) to limitate the vertex movement along the choosen axis.