bug#42406: Mouse-wheel scrolling can be flickering

[Eli Zaretskii]

> Cc: alan@idiocy.org, 42406@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Wed, 16 Dec 2020 09:46:59 +0100
> 
>  > As long as you invoke scrolling commands (and that's what the scroll
>  > bar eventually does in Emacs), you will always have the same problem:
>  > scrolling commands cause Emacs redraw all the frames.
> 
> Because it has to update mode lines or are there any other reasons?

Mode lines, header lines, and frame title.