[Gimp-user] Restricting tool movement along a single axis

[alemelo <forums gimpusers com>]

Hello,
as I write in the subject: is there a way to restrict tool movement along a
single (horizontal or vertical) axis?
I'm not talking about moving objects - as I checked and there's a thread for
that - but moving those little squares in the corners of a transform tool
selection.
Example: I want to change the perspective of a picture. I apply the perspective
tool and the picture is overlaid with a grid and four corners. I want to be able
to pick a corner - say the bottom right one - and move it *only* right or left,
without any vertical shift.

I tried with guidelines but I cannot make them stick to the exact side of the
image neither if I tell GIMP they're magnetic.
But what's worst is that even if I manually put guides along the edge, it seems
that the corners of the perspective tool ignore completely the magnetic
attribute.

In Photoshop I could simply pick one corner, hold the shift key and restrict
movement to the two main axes.

Any analog trick in GIMP?

Thanks.

am

-- 
alemelo (via www.gimpusers.com/forums)