Path: utzoo!utgpu!watmath!uunet!tut.cis.ohio-state.edu!CS.WISC.EDU!dave
From: dave@CS.WISC.EDU (Dave Cohrs)
Newsgroups: gnu.emacs
Subject: smooth scrolling
Message-ID: <8908021543.AA00534@romano.cs.wisc.edu>
Date: 2 Aug 89 15:43:14 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 33

Have you ever noticed that sometimes when you (scroll-up) or
(scroll-down), emacs (18.54) insists on doing really ugly things to your
display, like scrolling the entire display up/down (moving the banner
line) and then scrolling it back again?  Well, I figured out the reason
behind this.  When you have a message in the minibuffer, like "Mark
set", and you scroll, emacs tries to "optimize" the screen refresh, and,
instead of just clearing out the minibuf line, it does this wonderful
scrolling stuff.  Bletch!

That may be more efficient on an ascii terminal (I doubt it), but on a
bitmapped display, it is always ALWAYS cheaper to clean up a single line
that to scroll the entire window all over the place.

Below are two functions, (smooth-scroll-up) and (smooth-scroll-down)
that solve the problem without trying to hack the update optimizer.
You need to have the (update-display) function defined -- you can find
it in the Sun or X11 support.  Perhaps (update-display) should be pulled
out of these packages and put in a central place?

(defun smooth-scroll-up (arg)
  (interactive "P")
  (message "")
  (update-display)
  (scroll-up arg))

(defun smooth-scroll-down (arg)
  (interactive "P")
  (message "")
  (update-display)
  (scroll-down arg))

(define-key global-map "\C-v" 'smooth-scroll-up)
(define-key esc-map "v" 'smooth-scroll-down)