Constrain vertex to its face Here is a screenshot:


I want to use the scale tool to move the selected vertices closer to each other, but I want to do so without affecting the shape of the face. The normals of the two face may not be the same either (they might point in reflected directions, i.e. one measures 30 degrees and the other -30 degrees).

In 3ds max you can enable face constraints, and then all vertex movements happen only along a face. Is there such a thing in Blender? Or is there another way to achieve this.
One thing you can try is to scale selected vertices while locking normal Z axis.

To do so, enable Normal transform orientation with Alt+Space or from viewport header. Select vertices, enable Scale tool with S and press Shift+Z to lock movement along global Z axis, then Shift+Z once again to lock normal Z axis. After that move your mouse to change amount of effect.



It's also possible to move vertices as well while constraining normal Z axis making them roughly stay on the same surface.