I recorded what I saw and sent it as the attachment "bug_slow_motion.mp4".
Briefly, the child frame appeared, then moved downwards, and then resized.
The moving and resizing are very quick so I slowed down the video (about 10x slower).
There are two problems:
1. I wrap the set size and set position code in a `(let ((inhibit-redisplay t)) ...)'.
The docstring of `inhibit-redisplay' says "Non-nil means don’t actually do any redisplay.",
but the process of setting size and setting position is displayed.
2. In the code I gave, `set-frame-size' should be executed before `set-frame-position'.
But in fact, the child frame was first moved, and then resized. It is in the wrong order.
In GNU Emacs 29.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38,
cairo version 1.17.8)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Arch Linux
Configured using:
'configure --with-x-toolkit=gtk3 --with-native-compilation=aot
--sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
--with-tree-sitter --localstatedir=/var --with-cairo
--disable-build-details --with-harfbuzz --with-libsystemd
--with-modules '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'
'CXXFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions
-Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security
-fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSERTIONS -g
-ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto''
Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP 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.UTF-8
value of $XMODIFIERS: @im=fcitx
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
line-number-mode: t
indent-tabs-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 mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
comp comp-cstr warnings icons subr-x rx cl-seq cl-macs gv cl-extra
help-mode bytecomp byte-compile cl-lib sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils rmc iso-transl tooltip cconv
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd
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font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
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romanian slovak czech european ethiopic indian cyrillic chinese
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overlay sha1 md5 base64 format env code-pages mule custom widget keymap
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
native-compile emacs)
Memory information:
((conses 16 79379 8930)
(symbols 48 7147 0)
(strings 32 19698 1723)
(string-bytes 1 576171)
(vectors 16 16564)
(vector-slots 8 334975 11306)
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(intervals 56 420 0)
(buffers 984 14))