GTK-scrollbar doesn't move over blank lines

[Stephen Berman]

I don't know if the following is a bug or expected (though AFAICT not
documented) behavior.

1. emacs -Q
2. Insert several lines of text, then insert several blank lines (the
more blank lines, the more obvious the issue), then several more lines
of text.
3. Scroll using either the mouse wheel or by clicking the arrows at
the top or bottom of the scroll bar with mouse-1.  When the lines of
text scroll into or out of view at the top of the window, the scroll
bar thumb moves correspondingly up or down.  But when scrolling over
blank lines at the top of the window, the scroll bar thumb remains
(more or less) still, not adjusting its position within the trough as
it does when scrolling over text.

This doesn't happen in Emacs 21 with the Xaw3d scroll bar (I can't
test it with that scroll bar now in CVS Emacs), but I wonder if it's a
GTK manifestation of the way Emacs treats scrolling over blank lines,
cf. http://article.gmane.org/gmane.emacs.pretest.bugs/12311/


In GNU Emacs 22.0.50.14 (i686-pc-linux-gnu, GTK+ Version 2.8.10)
 of 2006-04-17 on escher
X server distributor `The X.Org Foundation', version 11.0.60802000
configured using `configure '--with-x-toolkit=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: en_US.UTF-8
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Major mode: Summary

Minor modes in effect:
  tabbar-mwheel-mode: t
  tabbar-mode: t
  recentf-mode: t
  show-paren-mode: t
  display-time-mode: t
  tooltip-mode: t
  auto-compression-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  temp-buffer-resize-mode: t
  column-number-mode: t
  line-number-mode: t

Recent input:
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<help-echo> <help-echo> <select-window> <help-echo> 
<down-mouse-5> <mouse-5> <down-mouse-5> <mouse-5> <double-down-mouse-5> 
<double-mouse-5> <triple-down-mouse-5> <triple-mouse-5> 
<triple-down-mouse-5> <triple-mouse-5> <triple-down-mouse-5> 
<triple-mouse-5> <down-mouse-5> <mouse-5> <down-mouse-5> 
<mouse-5> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <f11> <return> M-x r e p o <tab> 
r <tab> b <tab> <return>

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