[X3D-Public] Any way to do a 'LineSensor' (Like PlaneSensor but in one dimension)

[Dave A]

  I need to be able to drag objects along one dimension only, and I'd 
like the interaction to look natural too.

A PlaneSensor can let you drag things, and restrict *movement* using the 
min/max fields (set them to the same value, say, 0).

The problem is, they *detect* mouse movement in both directions, and 
arbitrary movement always produces some movement in both directions. The 
result is, for example, moving the mouse up/down the screen produces 
movement right/left in the object. This is bad.

So, is there any way to restrict the detection of mouse movement? Is 
there a different type of sensor available. I'm using Contact, maybe 
they have something handy?

Dave A.