Feature Request: Allow limiting zooming to certain direction

[vendillah]

I'd like to request a nice to have feature, which is zooming in a certain direction. Perhaps toggle it with key presses x or y, and have them being displayed as toggle buttons? I'm not sure what the best UI paradigms is for that.

Below you see my usecase - yes, here I am with the gaussian functions again :-) The red function "completely" fits my screen (before being practically zero), but I have to zoom in to have a better view of the differences, and thereby loosing the global view. It would be nice if I could make use of the entire height of the window by zooming only in the y-axis.

I can imagine x-zooming being useful for certain cases as well.