Scrollbar Knob Unexpectedly Changes Size When Scrolling

[Samuel Padgett]

This bug report will be sent to the Free Software Foundation,
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Please write in English, because the Emacs maintainers do not have
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In GNU Emacs 20.7.1 (i386-redhat-linux-gnu, X toolkit)
 of Thu Aug 24 2000 on porky.devel.redhat.com
configured using `configure  --mandir=/usr/share/man --infodir=/usr/share/info 
--prefix=/usr --libexecdir=/usr/lib --sharedstatedir=/var --with-gcc --with-pop 
--with-x-toolkit i386-redhat-linux-gnu'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

This is perhaps a subtle complaint, but the following has always
bothered me:

Whenever I scroll up and down through the contents of a buffer using
the C-v and M-v keys, I notice that the scrollbar knob changes size,
even though the buffer contents have not changed.  The change is very
small, but perceptible, particularly when scrolling quickly.

Typically, the size of a scrollbar knob is directly proportional to
the percentage of lines that are visible: If a buffer contains 100
lines and the window height is 10 lines, the knob should be exactly
1/10th the size of the scrollbar trough.  It should remain this size
as the user pages through the buffer as long as the buffer's contents
do not change and the window's height does not change.

It seems like Emacs is determining the size of the scrollbar knob by
the percentage of /characters/ that are visible, not lines.  It's
disconcerting to see the knob resize unexpectadly as you type and
scoll, and this behavior can be confusing to new users because it
looks like the buffer's contents are changing out from under them.  It
is also inconsistent with just about every other application I've ever
used.


Recent input:
up up up up up up up up up up up up up up up up up 
up up up up up up up up up up up C-h l C-n C-n C-n 
C-h l C-x 1 SPC u u m b u tab g s tab return SPC SPC 
SPC SPC SPC SPC SPC SPC SPC SPC SPC SPC SPC SPC b SPC 
SPC SPC SPC SPC SPC SPC SPC SPC C-h l C-x 1 SPC SPC 
SPC SPC SPC u l p SPC SPC d C-h l C-x 1 M-x r e p tab 
o r tab return

Recent messages:
Making completion list...
Mark set
Type C-x 1 to remove help window.  M-C-v to scroll the help.
Composing main Info directory...
Mark set
Composing main Info directory...done
Type C-x 1 to remove help window.  M-C-v to scroll the help.
Making completion list...
Loading emacsbug...
Loading emacsbug...done