Stefan Kangas <stefan@marxist.se> writes:

> > What is expected is that mouse scrolling in the non-selected window
> > will affect the non-selected window.  Does this need to be changed?
>
> I'm not sure, but I think I agree with you that it should be changed.
> Perhaps we could try it and see if it feels better?

It turns out there is already a defcustom 'mouse-wheel-follows-mouse'
that controls this behaviour when scrolling.  If non-nil (the default)
it will scroll the window that the mouse pointer is over, otherwise
the one where point is.  So the job is not that hard: we should just
do what the user wants.

The attached patch makes changing font size respect that option.  What
do you think?

Best regards,
Stefan Kangas