bug#68786: 30.0.50; Horizontal overscroll

[Eli Zaretskii]

> From: Andrey Listopadov <andreyorst@gmail.com>
> Cc: 68786@debbugs.gnu.org
> Date: Mon, 29 Jan 2024 20:53:34 +0300
> 
> > ... I won't object to such a feature, provided that it's optional and
> > OFF by default, and also that it is supported on as many toolkits as
> > is practical.  Patches welcome.
> 
> Fair enough.  Right now I can't send a patch, because I don't have the
> solution for this problem.  The piece of code I sent works for me, but
> it's not general by any means, and has a lot of subtle flaws.
> 
> Maybe if you could point me out to parts of Emacs that do the
> calculation of the longest visible line for the scroll bar so I could
> adopt it instead of doing hacky unscallable-face-font-width-based
> calculation?  Or maybe help me think of a better way to calculate this.

That calculation is in xdisp.c:set_horizontal_scroll_bar, which also
sets the size of the scroll-bar thumb.