From: lee <lee@yagibdah.de>
To: help-gnu-emacs@gnu.org
Subject: Re: prevent scroll-lock-mode from scrolling?
Date: Mon, 20 Jun 2016 17:24:53 +0200 [thread overview]
Message-ID: <87twgnhohm.fsf@heimdali.yagibdah.de> (raw)
In-Reply-To: 87y4609nv5.fsf@gmail.com
Dmitry Alexandrov <321942@gmail.com> writes:
> lee <lee@yagibdah.de> writes:
>> Can you explain to me why the cursor remains at its position /on the
>> screen/ while I'm scrolling with scroll-lock-mode enabled all the time
>> like it should --- and then suddenly moves when the top or bottom of the
>> buffer contents come into view? That doesn't make any sense to me; the
>> cursor still shouldn't move.
>
> Given that there is no free space before the first line of a buffer,
> this does make perfect sense with regard to scrolling backward (to the
> top of a buffer). The other way we would just get stuck with the point
> in the middle of a screen not being able to reach first lines. The
> scrolling forward behaves the same way for sake of coherence, I guess.
There is no free space beyond the last line of a buffer, either.
It doesn't make sense, though, because scroll-lock means that the cursor
does not move when scrolling. Why else would I use scroll-lock-mode?
> Anyway, if you look into the code, you’ll see that this behaviour is
> definetely intentional:
>
> (defun scroll-lock-next-line (&optional arg)
> "Scroll up ARG lines keeping point fixed."
> (interactive "p")
> (or arg (setq arg 1))
> (scroll-lock-update-goal-column)
> (if (pos-visible-in-window-p (point-max))
> (forward-line arg)
> (scroll-up arg))
> (scroll-lock-move-to-column scroll-lock-temporary-goal-column))
>
> (defun scroll-lock-previous-line (&optional arg)
> "Scroll up ARG lines keeping point fixed."
> (interactive "p")
> (or arg (setq arg 1))
> (scroll-lock-update-goal-column)
> (condition-case nil
> (scroll-down arg)
> (beginning-of-buffer (forward-line (- arg))))
> (scroll-lock-move-to-column scroll-lock-temporary-goal-column))
"Scroll up ARG lines keeping point fixed.": It doesn't keep point fixed
(as I expect) but moves it when the end or start of buffer are near
(which defeats the mode).
> However, if you do not like it, just remove the condition:
>
> (defun my-scroll-lock-next-line (&optional arg)
> "Scroll up ARG lines keeping point fixed."
> (interactive "p")
> (or arg (setq arg 1))
> (scroll-lock-update-goal-column)
> (scroll-up arg)
> (scroll-lock-move-to-column scroll-lock-temporary-goal-column))
>
> (defun my-scroll-lock-previous-line (&optional arg)
> "Scroll up ARG lines keeping point fixed."
> (interactive "p")
> (or arg (setq arg 1))
> (scroll-lock-update-goal-column)
> (scroll-down arg)
> (scroll-lock-move-to-column scroll-lock-temporary-goal-column))
>
> (advice-add 'scroll-lock-next-line :override #'my-scroll-lock-next-line)
> (advice-add 'scroll-lock-previous-line :override #'my-scroll-lock-previous-line)
Thank you very much! That does the trick --- and I just found out that
I have scroll-preserve-screen-position set to t and forgot about it ages
ago. The result of that is pretty much what scroll-lock-mode is
supposed to do.
I guess I'm a bit confused because emacs at work and emacs at home are
configured differently. I should be fine when I set
scroll-preserve-screen-position to t at work, too.
> Also, if you are regularily toggling the ‘scroll-lock-mode’ on and off,
> you might consider to use approach that, one might say, is more
> ‘Emacsish’ — another keychord instead of mode:
>
> (setq scroll-preserve-screen-position 'always)
> (global-set-key (kbd "M-n") #'scroll-up-line)
> (global-set-key (kbd "M-<down>") #'scroll-up-line)
> (global-set-key (kbd "M-p") #'scroll-down-line)
> (global-set-key (kbd "M-<up>") #'scroll-down-line)
The idea was to make use of the ScrollLock key. So I did that and found
that when scroll-lock-mode is enabled, the point does move when it
shouldn't.
Since what scroll-lock-mode does is achieved by setting
scroll-preserve-screen-position to t, what is the point or purpose of
scroll-lock-mode? That the cursor moves when it shouldn't?
BTW, it seems that changing scroll-preserve-screen-position requires
restarting emacs to take effect. Maybe that's what scroll-lock-mode is
for, being able to change the behaviour without restarting?
--
GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, X toolkit)
of 2016-03-18 on heimdali
next prev parent reply other threads:[~2016-06-20 15:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-17 1:12 prevent scroll-lock-mode from scrolling? lee
2016-06-17 1:25 ` Emanuel Berg
2016-06-17 4:14 ` Stefan Monnier
2016-06-17 6:00 ` Emanuel Berg
2016-06-17 22:40 ` Stefan Monnier
2016-06-18 1:19 ` what to require (was: Re: prevent scroll-lock-mode from scrolling?) Emanuel Berg
2016-06-17 22:47 ` prevent scroll-lock-mode from scrolling? lee
2016-06-17 6:47 ` Eli Zaretskii
2016-06-17 23:10 ` lee
2016-06-18 8:38 ` Eli Zaretskii
2016-06-19 23:54 ` lee
2016-06-20 8:33 ` tomas
2016-06-20 14:32 ` lee
2016-06-20 10:05 ` Dmitry Alexandrov
2016-06-20 15:24 ` lee [this message]
2016-06-20 16:12 ` Dmitry Alexandrov
2016-06-20 19:50 ` lee
2016-06-20 14:34 ` Eli Zaretskii
2016-06-20 21:21 ` lee
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