Bug: ruler-mode breaks scroll-conservatively (HEAD)

Bug: ruler-mode breaks scroll-conservatively (HEAD)

[Karl Chen]

This bug exists in Emacs HEAD 2002-12-14. Emacs 21.2 with ruler-mode.el from
HEAD has a similar problem.

Synopsis:

     emacs-21-3.50 -q    # in X (the bug doesn't occur with -nw)

     C-x C-f file_with_more_lines_than_window_height.txt

     M-x set-variable scroll-conservatively 99999

     ;; Scrolling occurs one line at a time when the cursor moves past the
     ;; first or last lines in the window (expected/desired behavior)

     M-x ruler-mode

     ;; Moving point past to/past the last line of the window recenters it
     ;; rather than scrolling by one line (bug).

Actually if you try to even move to the last displayable line in the window
(e.g. <down>, clicking on the last line, resizing the window smaller), it
recenters. So actually, ruler-mode breaks being able to have point on the last
line of the window.  Moving point upward isn't affected. Setting scroll-step
to 1 has the same problem.

In Emacs 21.2 with ruler-mode.el from HEAD, the problem exists slightly
differently. Point can exist on the first and last lines in the window, but
scrolling behaves non-conservatively when you move past the top/bottom.

This may ahve to do with the fact that with ruler-mode on, the last line of
text has one or two pixels less than without it.

--
Karl Chen / quarl@quarl.org



In GNU Emacs 21.3.50.8 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-12-14 on quack.quarl.org
configured using `configure '--prefix=/usr/local/stow/emacs' 'CC=distcc''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Re: Bug: ruler-mode breaks scroll-conservatively (HEAD)

[Juanma Barranquero]

On Sun, 15 Dec 2002 12:50:20 -0800, Karl Chen <quarl@hkn.eecs.berkeley.edu> wrote:

> Synopsis:
> 
>      emacs-21-3.50 -q    # in X (the bug doesn't occur with -nw)
> 
>      C-x C-f file_with_more_lines_than_window_height.txt
> 
>      M-x set-variable scroll-conservatively 99999
> 
>      ;; Scrolling occurs one line at a time when the cursor moves past the
>      ;; first or last lines in the window (expected/desired behavior)
> 
>      M-x ruler-mode
> 
>      ;; Moving point past to/past the last line of the window recenters it
>      ;; rather than scrolling by one line (bug).

This problem has already been reported several times. The behavior
appeared after a patch by RMS to fix a bug in the redisplay of
partially-visible lines.

See:

http://mail.gnu.org/pipermail/emacs-devel/2002-July/010505.html
http://mail.gnu.org/pipermail/emacs-devel/2002-July/010512.html
http://mail.gnu.org/pipermail/emacs-devel/2002-July/010588.html
http://mail.gnu.org/pipermail/emacs-devel/2002-September/012049.html
http://mail.gnu.org/pipermail/emacs-devel/2002-September/012539.html

for part of the little bugger's history.

> This may ahve to do with the fact that with ruler-mode on, the last line of
> text has one or two pixels less than without it.

Yes. In fact, anything that would make the last line of the window to be
only partially visible should trigger the bug.

                                                           /L/e/k/t/u