Feature-request: scroll-bar-granularity

[David Kastrup]

In GNU Emacs 21.1.1 (i586-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-10-22 on tupik.goethe.zz
configured using `configure  --prefix=/usr/local/emacs-21'
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.ISO8859-1
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

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

With the advent of variable-height text and inline images, scrolling
with the help of the scroll bar has become unintuitive: lines can
easily become tall; particularly when images are involved, even taller
than the screen.

In that case, using the scroll bars for scrolling can become quite
unintuitive.

I propose that
a) scrolling always orients itself on real screen estate.  This
includes the behavior of the Page-Up/Page-Down keys.  Where line
numbers come into account (like in the variable
next-screen-context-lines), they are converted into screen-estate
distances by multiplying them with the height of the current default font.

b) window-vscroll is taken into account when calculating the new
scrolling position.  If the resulting window-vscroll can conceptually
be made less in absolute value to scroll-bar-granularity, the
corresponding line will be made the top line of the window and
window-vscroll will be set to 0.  If not, the exact calculated value
of window-vscroll will be used instead.

The effect will be that when scrolling, the screen will snap to whole
lines only whenever this does not change the window beginning too much.

A necessity for navigating in buffers with larger inline images and
fonts.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum
Email: David.Kastrup@t-online.de