Problems with recenter.

[Matt Hodges]

In GNU Emacs 21.3.50.1 (i686-pc-linux-gnu, GTK+ Version 2.4.13)
 of 2004-11-10 on dugong
Distributor `The XFree86 Project, Inc', version 11.0.40300001
configured using `configure '--with-gtk''

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: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

I sometimes see problems when using recenter with a negative-argument.
I think this is restricted to certain combinations of header-line
(inherited from mode-line) and default fonts. In particular, I see
problems with the following:

    (progn
      (set-frame-font
       "-xos4-terminus-medium-r-normal--20-200-72-72-c-100-iso8859-1")
      (set-face-attribute 'modeline nil :box nil :family "helv"))

(On Debian, this font is from the xfonts-terminus package, and was
apparently downloaded from <URL:http://www.is-vn.bg/hamster/>.)

After emacs -Q, then C-h i, and scrolling up by more than one full
screen:

 (1) With point at the start of a line, M-- C-l causes point to move
     up one line. The line which point was on is visible, and using
     C-n to move onto it causes a redisplay, with the original line
     centered in the window (like after C-l with no prefix arg).
     
 (2) With point not at the start of a line, M-- C-l acts like C-l;
     point is unchanged.

Perhaps related to this, but not requiring the font customizations
above, I also see the following problems. Run emacs -Q, M-x
customize-face RET default RET, then C-x 2.

 (1) In the upper window, with M-> then M-- C-l, I see a flicker as if
     two redisplays have happened. This is more obvious if M-- C-l is
     repeated.

 (2) In the lower window, after M-> then M-- C-l, only the top of the
     line displaying the cursor is visible. Trying M-- C-l on several
     of the lines above this, various proportions of the line
     displaying the cursor are visible; moving forward with C-f on a
     partially visible line, a redisplay occurs (with point
     recentered) after the button widget is passed.

(In these cases, the font is
-Adobe-Courier-Medium-R-Normal--17-120-100-100-M-100-ISO8859-1).

Thanks,

Matt