bug#69534: Scrolling up causes all text to shift drastically when cursor hits bottom of viewable area.

bug#69534: Scrolling up causes all text to shift drastically when cursor hits bottom of viewable area.

[Arkdae via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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Start 'emacs -Q'. Open a long document which is longer than can fit in
the window all at once. C-x 2 to split into two windows. Drag with the
mouse on the information bar with button one to shrink the bottom
window a bit. Then grab the scroll bar in the top window and drag up.

The cursor reaches the bottom. Then I slowly scroll one more pixel up
and all of the text contents are repositioned with the cursor at the
middle. The next pixel scrolled up keeps the cursor in the middle and
corrects the text to where it should have been.

Scrolling at normal speed causes flickering due to this, and when I am
trying to follow my place to see where I need to get to, it is hard due
to this shifting every half-page. Scrolling down does not shift the
text in this way, and the cursor correctly moves to stay within the
viewable area.

In GNU Emacs 29.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.40,
cairo version 1.18.0)
Windowing system distributor 'The X.Org Foundation', version
11.0.12101011
System Description: Arch Linux

Configured using:
 'configure --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
 --with-tree-sitter --localstatedir=/var --with-cairo
 --disable-build-details --with-harfbuzz --with-libsystemd
 --with-modules --with-x-toolkit=gtk3 'CFLAGS=-march=x86-64
 -mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=2
 -Wformat -Werror=format-security -fstack-clash-protection
 -fcf-protection -g
 -ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto'
 'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -
flto=auto''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US
  locale-coding-system: iso-latin-1-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
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mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date network-stream puny nsm files-x cl-extra help-mode
ace-window avy slime-fancy slime-indentation slime-cl-indent cl-indent
slime-trace-dialog slime-fontifying-fu slime-package-fu slime-
references
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bridge slime-macrostep macrostep slime-mdot-fu slime-enclosing-context
slime-fuzzy slime-fancy-trace slime-fancy-inspector slime-c-p-c
slime-editing-commands slime-autodoc slime-repl slime-parse slime
easy-mmode apropos compile text-property-search etags fileloop
generator
xref project arc-mode archive-mode noutline outline icons pp comint
ansi-osc ansi-color ring hyperspec thingatpt ace-window-autoloads
avy-autoloads package browse-url url url-proxy url-privacy url-expand
url-methods url-history url-cookie generate-lisp-file url-domsuf
url-util mailcap url-handlers url-parse auth-source cl-seq eieio
eieio-core cl-macs password-cache json subr-x map byte-opt gv bytecomp
byte-compile url-vars cl-loaddefs cl-lib rmc iso-transl tooltip cconv
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
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hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 122838 9467)
 (symbols 48 13323 2)
 (strings 32 45474 2514)
 (string-bytes 1 1178662)
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bug#69534: Scrolling up causes all text to shift drastically when cursor hits bottom of viewable area.

[Eli Zaretskii]

> Date: Sun, 03 Mar 2024 15:56:36 +0000
> From:  Arkdae via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Start 'emacs -Q'. Open a long document which is longer than can fit in
> the window all at once. C-x 2 to split into two windows. Drag with the
> mouse on the information bar with button one to shrink the bottom
> window a bit. Then grab the scroll bar in the top window and drag up.
> 
> The cursor reaches the bottom. Then I slowly scroll one more pixel up
> and all of the text contents are repositioned with the cursor at the
> middle. The next pixel scrolled up keeps the cursor in the middle and
> corrects the text to where it should have been.

I cannot reproduce this, but then I don't think I understand what you
mean by "scroll one more pixel up".  AFAIK, scrolling text in Emacs
works by lines, not by pixels.  Maybe a GTK3 build allows pixelwise
scrolling via the scroll-bar?  If so, this could be specific to GTK3
builds or something.

Are you sure you don't have some local changes wrt stock Emacs 29.2,
or maybe activated some non-default feature that affects scrolling?

bug#69534: Scrolling up causes all text to shift drastically when cursor hits bottom of viewable area.

[Arkdae via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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What I am trying to say is, when the point gets to the bottom of a
window, and you move the scroll bar up the smallest amount you can,
then the point and the text all move to the middle. Then you move the
scroll bar up one more tiny amount and the text shifts back down to
where it should have been for normal line scrolling.

But, really if you don't see it, you don't have the problem. It's
reasonably obvious. It is a good point that you made, and so I tried a
different GTK theme. I believe the default is Adwaita, so I started
Emacs like so:

GTK_THEME=Adiaita emacs -Q

But it still occurs, but maybe not quite as often.

Otherwise, I can't say that I am aware of any customization to Emacs.
I'm rather new to using it. The only extensions I use are slime and
ace-window.

On Mon, 2024-03-04 at 14:15 +0200, Eli Zaretskii wrote:
> > Date: Sun, 03 Mar 2024 15:56:36 +0000
> > From:  Arkdae via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> > 
> > Start 'emacs -Q'. Open a long document which is longer than can fit
> > in
> > the window all at once. C-x 2 to split into two windows. Drag with
> > the
> > mouse on the information bar with button one to shrink the bottom
> > window a bit. Then grab the scroll bar in the top window and drag
> > up.
> > 
> > The cursor reaches the bottom. Then I slowly scroll one more pixel
> > up
> > and all of the text contents are repositioned with the cursor at
> > the
> > middle. The next pixel scrolled up keeps the cursor in the middle
> > and
> > corrects the text to where it should have been.
> 
> I cannot reproduce this, but then I don't think I understand what you
> mean by "scroll one more pixel up".  AFAIK, scrolling text in Emacs
> works by lines, not by pixels.  Maybe a GTK3 build allows pixelwise
> scrolling via the scroll-bar?  If so, this could be specific to GTK3
> builds or something.
> 
> Are you sure you don't have some local changes wrt stock Emacs 29.2,
> or maybe activated some non-default feature that affects scrolling?


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bug#69534: Scrolling up causes all text to shift drastically when cursor hits bottom of viewable area.

[Eli Zaretskii]

> Date: Thu, 07 Mar 2024 02:13:22 +0000
> From: Arkdae <arkdae@lnx.graphics>
> Cc: 69534@debbugs.gnu.org
> 
> What I am trying to say is, when the point gets to the bottom of a
> window, and you move the scroll bar up the smallest amount you can,
> then the point and the text all move to the middle. Then you move the
> scroll bar up one more tiny amount and the text shifts back down to
> where it should have been for normal line scrolling.
> 
> But, really if you don't see it, you don't have the problem. It's
> reasonably obvious. It is a good point that you made, and so I tried a
> different GTK theme. I believe the default is Adwaita, so I started
> Emacs like so:
> 
> GTK_THEME=Adiaita emacs -Q
> 
> But it still occurs, but maybe not quite as often.
> 
> Otherwise, I can't say that I am aware of any customization to Emacs.
> I'm rather new to using it. The only extensions I use are slime and
> ace-window.

Strange.  Can anyone else reproduce this weird display issue?