bug#18990: 25.0.50; Scroll bar display problems

[martin rudalics]

> Starting Emacs like this:
>
> emacs -Q --eval "(progn (modify-all-frames-parameters '((scroll-bar-width . 7))) 
(custom-set-variables '(scroll-bar-mode (quote left))))"
>
> the scroll bar is correctly display on the left, but its width is the
> default, not the customized value, and it overlays the left fringe,
> which is hence hidden.

There are two ways to change the width or height of a scroll bar with
GTK: Either by choosing an appropriate theme or by setting the
slider-width in a configuration file.  You can't change the size
individually from within Emacs and IMO we should prevent users from
trying to do so.  What happens currently is that Emacs internally uses
the height you specified and GTK continues to draw the scroolbar in its
default size over it.

> These display problems do not happen when the scroll bar is either on
> the right or has its default width.

There are similar problems, for example, with side-by-side windows.

> They also don't happen with the
> non-toolkit-scroll-bar build.  They do happen with 24.3, the earliest
> version I currently have (I don't have a non-toolkit-scroll-bar build of
> 24.4 at hand but I guess it also has the problems).

Non-GTK scroll bars should not have any such problems.

> (I haven't noticed
> these problems before, since I've been using non-toolkit-scroll-bar
> builds for a long time, and only since the 24.4 release have switched to
> the toolkit scroll bar on the trunk to be able to test the horizontal
> scroll bar.)

The GTK horizontal scroll bar has similar problems.

martin