Re: scrollbar (no toolkit) display bug

[Raphaël Berbain]

Gerd Moellmann writes:

> raphael.berbain@bigfoot.com (Raphaël Berbain) writes:
> 
>> Anyway, I'll try to find a way to make it appear.  In the worst case
>> with Gnus, it sometimes shows up but I'll try to find a simpler way
>> because this one involves all my usual setup.

OK, here we go:

I ran the tests with 21.1 release, and with 21.1 with xterm.c patched,
with the scrollbar on the left side or on the right side.  As far as I
can tell, the size of the scrollbar isn't relevant, as long as it's
smaller than the default size.  However, depending on this size, the
bug is more or less visible.  I just tried to choose values for which
the glitch was the most visible.

Each time, I started Emacs, did a screen capture, hit space, and re did
a screenshot.

I used two files:

,----[ left.el ]
| (add-to-list 'default-frame-alist '(scroll-bar-width . 12))
`----

,----[ right.el ]
| (add-to-list 'default-frame-alist '(scroll-bar-width . 10))
| (set-scroll-bar-mode 'right)
`----

I invoked Emacs like this:
emacs -geometry 30x20 -q --no-site-file -l [left|right].el

"appres Emacs" yields:
Emacs*Font: -ETL-Fixed-Medium-R-Normal--16-160-72-72-C-80-ISO8859-1

Screenshots are available at: http://raphael.berbain.free.fr.
and are named [release|patched]-[left|right]-[before|after].png

The following table sums up in which case I saw a display problem.

scrollbar |      |
on the -> | left | right
----------+------+-------
release   | ! OK | ! OK
----------+------+-------
patched   |  OK  | ! OK

[OK means no bug, ! OK means bug]

And I guess this is it.  I hope you'll be able to reproduce this
behavior, as I have no idea how to make it more deterministic.  Maybe
you'll have to tweak the scroll bar width in order to see the bug, the
"suitable" size depends on the font and on the S.B. position: e.g. on my
system, with the default font, for the scroll bar on the right, 6 is a
good value to see the problem.

-- 
Raphaël