Subject: bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

From: Rahguzar <[email-masked]>
Date: Thu, 10 Aug 2023 19:05:03 +0200

Dear Emacs developers,

To reproduce starting from 'emacs -Q' visit an image file. Then
repeatedly use 'i +' till the image is taller than the window. The
image can be scrolled using mouse wheel. Now do

M-x pixel-scroll-precision-mode

After this attempting to scroll the image will set the vscroll to 0
and then image can't be scrolled at all.

>From some investigation it seems like this behavior is not specific
to image-mode. Another way to reproduce the behavior is to evaluate
the following lisp code,

(let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
       (height (* (window-text-height win t) 2))
       (file "path/to/image"))
  (select-window win)
  (erase-buffer)
  (insert-image (create-image file nil nil))
  (goto-char 1)
  (pixel-scroll-precision-mode)
  nil)

This image thus displayed can not be scrolled. However if the code
above is slightly modified to insert a new line after the image,
scrolling can be done normally, i.e.

(let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
       (height (* (window-text-height win t) 2))
       (file "path/to/image"))
  (select-window win)
  (erase-buffer)
  (insert-image (create-image file nil nil))
  (insert "\n")
  (goto-char 1)
  (pixel-scroll-precision-mode)
  nil)

produces an image that can be scrolled. Inserting a newline after the
text covered by the text property holding the image also fixes the
problem in 'image-mode' but that doesn't seem like the right fix to me.

Rahguzar

In GNU Emacs 29.1 (build 1, x86_64-suse-linux-gnu, GTK+ Version 3.24.38,
 cairo version 1.17.8) of 2023-08-07 built on lamb11
System Description: openSUSE Tumbleweed

Configured using:
 'configure --host=x86_64-suse-linux-gnu --build=x86_64-suse-linux-gnu
 --program-prefix= --disable-dependency-tracking --prefix=/usr
 --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin
 --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include
 --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-pgtk --with-native-compilation=aot
 --with-cairo --with-libotf --with-jpeg --with-tiff --with-gif
 --with-png --with-rsvg --with-xft --with-xml2 --with-dbus --with-sound
 --with-json --with-mailutils --with-gnutls --with-tree-sitter
 --enable-locallisppath=/usr/share/emacs/29.1/site-lisp:/usr/share/emacs/site-lisp
 'CFLAGS=-O2 -Wall -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3
 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables
 -fstack-clash-protection -Werror=return-type -flto=auto'
 LDFLAGS=-Wl,-O2'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY
PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER XIM GTK3 ZLIB

Important settings:
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  locale-coding-system: utf-8-unix

Major mode: mu4e:main

Minor modes in effect:
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  dirvish-override-dired-mode: t
  server-mode: t
  pixel-scroll-precision-mode: t
  repeat-mode: t
  evil-mode: t
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  windmove-mode: t
  +popup-mode: t
  +modeline-global-mode: t
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  global-eldoc-mode: t
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  font-lock-mode: t
  window-divider-mode: t
  buffer-read-only: t
  size-indication-mode: t
  line-number-mode: t
  transient-mark-mode: t
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  auto-encryption-mode: t
  auto-compression-mode: t
  abbrev-mode: t

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Memory information:
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