GNU bug report logs - #22395
25.0.50; 'C-v' scrolls only a half of the window height

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#22395: closed (25.0.50; 'C-v' scrolls only a half of the
 window height)
Date: Mon, 18 Jan 2016 16:26:02 +0000

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Your message dated Mon, 18 Jan 2016 18:25:24 +0200
with message-id <83y4bmdfd7.fsf <at> gnu.org>
and subject line Re: bug#22395: 25.0.50; 'C-v' scrolls only a half of the window height
has caused the debbugs.gnu.org bug report #22395,
regarding 25.0.50; 'C-v' scrolls only a half of the window height
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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22395: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22395
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From: Dani Moncayo <dmoncayo <at> gmail.com>
To: bug-gnu-emacs <bug-gnu-emacs <at> gnu.org>
Subject: 25.0.50; 'C-v' scrolls only a half of the window height
Date: Sun, 17 Jan 2016 21:50:16 +0100

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Recipe from "emacs -Q":

1. Eval:
    (setq scroll-preserve-screen-position t)
    (setq scroll-margin 2)

2. Visit the attached file.

On my system, I initially see lines 1 to 33.

3. Type 'C-v'

I observe that 'C-v' has scrolled the buffer vertically, but only by
about a half of the window height (I now see lines 16 to 48).
Subsequent 'C-v' commands do the same: they scroll the buffer by a
half of the window.

This seems wrong.  The amount of scrolling should be "a near full
screen", as described in 'C-h k C-v'.

I observe this bug also in the last 24.5 release.

In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2016-01-17 built on LEG570
Repository revision: a0d5b7ae3bb014bb0b1c205d123c597df0e76411
Windowing system distributor 'Microsoft Corp.', version 10.0.10586
Configured using:
 'configure --host=i686-pc-mingw32 --enable-checking=yes,glyphs'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

-- 
Dani Moncayo

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Dani Moncayo <dmoncayo <at> gmail.com>
Cc: 22395-done <at> debbugs.gnu.org
Subject: Re: bug#22395: 25.0.50; 'C-v' scrolls only a half of the window height
Date: Mon, 18 Jan 2016 18:25:24 +0200

> Date: Sun, 17 Jan 2016 21:50:16 +0100
> From: Dani Moncayo <dmoncayo <at> gmail.com>
> 
> 1. Eval:
>     (setq scroll-preserve-screen-position t)
>     (setq scroll-margin 2)
> 
> 2. Visit the attached file.
> 
> On my system, I initially see lines 1 to 33.
> 
> 3. Type 'C-v'
> 
> I observe that 'C-v' has scrolled the buffer vertically, but only by
> about a half of the window height (I now see lines 16 to 48).
> Subsequent 'C-v' commands do the same: they scroll the buffer by a
> half of the window.
> 
> This seems wrong.  The amount of scrolling should be "a near full
> screen", as described in 'C-h k C-v'.

Start the same recipe from line #3 or greater, and the "bug" goes
away.

You asked Emacs to do the impossible: preserve the screen position of
point at the first window line and also not to allow point to enter
the first 2 lines of the window.  Emacs didn't know what to do with
this conflict.  Now it does.

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