bug#75333: 31.0.50; Feature-Request: Always keep cursor's position when pixel scrolling

bug#75333: 31.0.50; Feature-Request: Always keep cursor's position when pixel scrolling

[Eason Huang]

Recently, when the cursor is inside the screen, it's positon will not
move when pixel scrolling. But when the cursor touching the bording of
window, it's position begin to change.

expected:

1. when the cursor(line) is closed to the border of window, partially-visible
the cursor
2. when the cursor(line) is outside the window, hide the cursor
3. wehn the cursor(line) is inside the window, show the cursor again

Or there already an option to enable this feature?

As I known, Apple Xcode and Microsoft Word have the same behavior as
describe above.

-- 
Eason Huang


In GNU Emacs 31.0.50 (build 1, x86_64-apple-darwin24.2.0, NS
 appkit-2575.30 Version 15.2 (Build 24C101)) of 2025-01-01 built on
 192.168.1.4
Windowing system distributor 'Apple', version 10.3.2575
System Description:  macOS 15.2

Configured using:
 'configure --without-native-compilation --without-dbus
 'CPPFLAGS=-I/opt/local/include
 -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk'
 'LDFLAGS=-L/opt/local/lib -Wl,-headerpad_max_install_names -Wl,-rpath
 /opt/local/lib/gcc14
 -Wl,-syslibroot,/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
 -arch x86_64''

Configured features:
ACL GIF GLIB GMP GNUTLS JPEG LCMS2 LIBXML2 MODULES NOTIFY KQUEUE NS
PDUMPER PNG RSVG SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER
WEBP XIM ZLIB

Important settings:
  value of $LANG: zh_CN.UTF-8
  locale-coding-system: utf-8-unix

Major mode: ELisp/l

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  blink-cursor-mode: t
  minibuffer-regexp-mode: 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:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils vc-git
diff-mode track-changes easy-mmode files-x vc-dispatcher cl-loaddefs
cl-lib china-util rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/ns-win ns-win ucs-normalize mule-util term/common-win tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads kqueue cocoa ns lcms2
multi-tty make-network-process tty-child-frames emacs)

Memory information:
((conses 16 46556 10009) (symbols 48 5998 0) (strings 32 15092 2485)
 (string-bytes 1 375037) (vectors 16 11182)
 (vector-slots 8 185208 10596) (floats 8 24 154) (intervals 56 508 38)
 (buffers 992 12))

bug#75333: 31.0.50; Feature-Request: Always keep cursor's position when pixel scrolling

[Eli Zaretskii]

> From: Eason Huang <aqua0210@foxmail.com>
> Date: Sat, 04 Jan 2025 08:50:04 +0800
> 
> 
> Recently, when the cursor is inside the screen, it's positon will not
> move when pixel scrolling. But when the cursor touching the bording of
> window, it's position begin to change.
> 
> expected:
> 
> 1. when the cursor(line) is closed to the border of window, partially-visible
> the cursor
> 2. when the cursor(line) is outside the window, hide the cursor
> 3. wehn the cursor(line) is inside the window, show the cursor again
> 
> Or there already an option to enable this feature?
> 
> As I known, Apple Xcode and Microsoft Word have the same behavior as
> describe above.

Unlike other editors, Emacs' display engine was designed with the
explicit requirement that the position of point (what you call
"cursor") is always visible in the window.  So when the window is
scrolled for some reason, Emacs moves point to bring it back into the
visible portion of the window.  This behavior is coded and assumed all
over the place, and is hard to change.  There's therefore no option
for the behavior you expect.

There was an effort in the past to provide such behavior as an option,
but AFAIR it wasn't completed.  We did discuss some of the
consequences of such behavior and identified some problematic
decisions which will need to be made in various situations (e.g., what
should happen when point is outside of the window and the user runs
some command which modifies the buffer?), and I personally consider
those issues we considered to be the tip of a very large iceberg.  See
this discussion:

  https://lists.gnu.org/archive/html/emacs-devel/2021-12/msg00328.html

bug#75333: 31.0.50; Feature-Request: Always keep cursor's position when pixel scrolling

[Eason Huang]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Eason Huang <aqua0210@foxmail.com>
>> Date: Sat, 04 Jan 2025 08:50:04 +0800
>> 
>> 
>> Recently, when the cursor is inside the screen, it's positon will not
>> move when pixel scrolling. But when the cursor touching the bording of
>> window, it's position begin to change.
>> 
>> expected:
>> 
>> 1. when the cursor(line) is closed to the border of window, partially-visible
>> the cursor
>> 2. when the cursor(line) is outside the window, hide the cursor
>> 3. wehn the cursor(line) is inside the window, show the cursor again
>> 
>> Or there already an option to enable this feature?
>> 
>> As I known, Apple Xcode and Microsoft Word have the same behavior as
>> describe above.
>
> Unlike other editors, Emacs' display engine was designed with the
> explicit requirement that the position of point (what you call
> "cursor") is always visible in the window.  So when the window is
> scrolled for some reason, Emacs moves point to bring it back into the
> visible portion of the window.  This behavior is coded and assumed all
> over the place, and is hard to change.  There's therefore no option
> for the behavior you expect.
>
> There was an effort in the past to provide such behavior as an option,
> but AFAIR it wasn't completed.  We did discuss some of the
> consequences of such behavior and identified some problematic
> decisions which will need to be made in various situations (e.g., what
> should happen when point is outside of the window and the user runs
> some command which modifies the buffer?), and I personally consider
> those issues we considered to be the tip of a very large iceberg.  See
> this discussion:
>
>   https://lists.gnu.org/archive/html/emacs-devel/2021-12/msg00328.html
>

Hi Eli,

Thanks for your explanation, it make sense.

-- 
Eason Huang