GNU bug report logs - #12401
scroll-preserve-screen-position broken with font height faces

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Message #26 received at 12401 <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 12401 <at> debbugs.gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>,
	l26wang <at> gmail.com
Subject: Re: bug#12401: scroll-preserve-screen-position broken with font	height
	faces
Date: Wed, 12 Sep 2012 10:08:48 +0200

>>> scroll-preserve-screen-position?  Is it just that doing N C-v's
>>> followed by N M-v's brings point to the same location where it was
>>> before this sequence of 2N commands?
>> I think this should be the main point, yes.
>
> For this to work, we would need to make sure that C-v followed by M-v
> end up with a window that has the same window-start as the one before
> C-v.

Why?

> But this is impossible to ensure with the way we compute
> window-start, because the move_it family of functions used for that
> can only move forward; therefore moving back is necessarily
> implemented differently, and the results differ when variable-size
> fonts are present.
>
> IOW, this is a limitation of the current design of the
> window-scrolling functions that can only be lifted by redesigning.

I'm completely happy with the following solution: Whenever, after a
sequence of scrolling commands, the original position (that is the
position before the sequence started) reappears in a window, move to
that position and leave the window start position alone.  See also

http://lists.gnu.org/archive/html/emacs-devel/2008-02/msg01892.html

martin

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