bug#18990: 25.0.50; Scroll bar display problems

[martin rudalics <rudalics@gmx.at>]

 > That possibility didn't occur to me.  Is there some command I can call,
 > or some other way to convince myself that this is what is happening (not
 > that I don't believe you, I'd just like to understand it).

I suppose the window manager simply crops everything that doesn't fit
within its external borders.  You should be able to convince yourself
for a single window frame by removing modeline and echo area and
decreasing the height of the horizontal scroll bar.

 > And why does
 > it happen on the right but not on the left (nor on the right side of a
 > non-right window)?

It doesn't happen on the left or for non-right windows because in this
case the (default sized) scroll bar gets drawn into Emacs' client area
and the window manager assumes that Emacs knows how to deal with it.

 > I meant Emacs can make it thinner, since it didn't occur to me that the
 > appearance of the right scroll bar could be due to the WM.

We must discriminate: Emacs reserves the area as you specify it.  Gtk
draws its slider into that area alas with a width determined by the
theme or a resource file.

 > Indeed: with (modify-all-frames-parameters '((scroll-bar-width . 32)))
 > the scroll bar

... more precisely, the slider ...

 > still has the default width but there are nearly equally
 > wide spaces on both sides of it (between the scroll and the fringe to
 > the left and between the scroll bar and the frame border to the right).
 > Ok, this convinces me that Emacs is not modifying the width.

... the width of the slider.

 > As I mentioned, I can't simply build both the Lucid and the Gtk builds
 > on my system, apparently due to incompatible libpng requirements.

Maybe Jan has an idea.

 > Anyway, it seems that the appropriate fix for this bug it to make
 > modifying the scroll-bar-width and scroll-bar-height frame parameters
 > noops in Gtk builds.

Another problem is that currently we prescribe a minimum width for
scroll bars which has parts of the scroll bar background change
appearance when the Gtk slider is narrower.

martin