bug#3956: Happens on Windows too

[Eli Zaretskii <eliz@gnu.org>]

> From: Ville-Markus Yli-Suutala <villemarkus.ylisuutala@gmail.com>
> Date: Sun, 22 Aug 2021 23:35:43 +0300
> Cc: 3956@debbugs.gnu.org
> 
> On Sun, Aug 22, 2021 at 9:06 AM Eli Zaretskii <eliz@gnu.org> wrote:
> >
> > > From: Ville-Markus Yli-Suutala <villemarkus.ylisuutala@gmail.com>
> > > Date: Sat, 21 Aug 2021 23:40:48 +0300
> > >
> > > Height of the scrollbar thumb changes while scrolling on Windows too.
> >
> > That's how the scroll-bar thumb was designed to work in Emacs.
> 
> By height changing I mean the tallness of the thumb, not its position
> on the scrollbar.

Yes, that's what I meant.

> My display resolution is 1920 x 1080. If I start
> Emacs with emacs -Q, click the maximize window button in the top right
> corner, and go to the tutorial by pressing C-h t. The scrollbar thumb
> is now 24 pixels tall. Now if I press C-v to scroll down, the
> scrollbar thumb grows to be 42 pixels tall.
> 
> Is it actually meant to work this way? GTK+ Emacs on my Debian machine
> does not change the size of the scrollbar thumb as I scroll.

The thumb reflects the size in characters, not in screen lines, so it
cannot be constant as you scroll, especially if lines in the buffer
differ a lot in their length.