bug#42406: Mouse-wheel scrolling can be flickering

[martin rudalics]

> Does “not necessarily” mean
>
> (a) if I dont’ have the mentioned problem now, I will never see it;
>
> or
>
> (b) I should not be surprised if I see it in three weeks, say.

(a) hopefully.  But note that this is just the isolated problem that
when you scroll the buffer and redisplay has to relocate point in the
buffer in order to make it visible, the current line number doesn't get
updated correctly in the mode line.  As Eli noted elsewhere, there might
be other things that don't get updated correctly.  Ideally, none of
these other things should be affected by scrolling but who knows what
users put into their 'window-scroll-functions' ...

Finally, I doubt that the two 'wset_update_mode_line' calls in
'wset_update_mode_line' are responsible for the flickering you see.  If
they are not, it might make sense to look for the real culprits.

martin