Re: The unwarranted scrolling assumption

[David Engster <deng@randomsample.de>]

Eli Zaretskii writes:
>> From: Lennart Borgman <lennart.borgman@gmail.com>
>> Date: Thu, 17 Jun 2010 20:32:27 +0200
>> Cc: emacs-devel@gnu.org, david@harpegolden.net
>> 
>> Several of us has said that the problem is easily reproduceable.
>
> Please show a recipe starting from "emacs -Q".

OK, I'll try. Using Emacs 23.2 GTK GNU/Linux:

* emacs -Q

* Insert in the *scratch* buffer:

  (setq scroll-preserve-screen-position 'always
      scroll-conservatively           most-positive-fixnum
      scroll-step                     0
      redisplay-dont-pause            t)

  and evaluate. These are the recommended settings given in this thread
  to get single-line scrolling.

* Insert the following and evaluate (adapt path accordingly):

  (dotimes (dummy 50)
    (insert-file-contents "~/emacs/share/emacs/23.2/etc/HELLO"))

* Now press <down> and hold key to scroll the buffer. The results will
  be different, depending on the default font and machine speed. On my
  machine (Celeron 900 @2.2GHz), the cursor sometimes jump to the middle
  or beginning of the window while scrolling.

  (BTW, I also notice that the cursor shape sometimes "sticks" in the
  "Hindi" line, but that's new to me).

Now this is just an example. As I've written, I've seen this behavior
for years, especially in large buffers when using different fonts,
elaborate font-locks, etc.

HTH,
-David