Thank you for your reply,
I have sent this bug report directly from my email (in a web browser)... so I guess I evaded the regular way of reporting bugs, thus helpful info from report-emacs-bug was not automatically attached.
Really sorry about that, I will add those details at the end of this message.
Also, I'm not sure if replying to you in this manner (directly through email) is good practice or not... sorry if it's not.
Unfortunately, even emacs running without cairo doesn't help. The issue remains. The same goes for harfbuzz.
As for double-buffering, wasn't it removed in emacs v25... so I'm not sure how/what to disable here?
As for advanced optimization features of my system... not sure if compton/picom can qualify as such, but nevertheless I've disabled it, however the issue was still there.
The previous emacs version was 26.3. and when I downgrade emacs to that version, the issue is gone. I will attach details collected by report-emacs-bug for that version as well.
Thanks
In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, cairo version 1.17.3)
of 2020-08-28 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
System Description: Arch Linux
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set [27 times]
Making completion list...
Configured using:
'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
--localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
--with-modules --with-cairo --with-harfbuzz 'CFLAGS=-march=x86-64
-mtune=generic -O2 -pipe -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'
Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP
Important settings:
value of $LC_TIME: sr_RS.UTF-8
value of $LANG: en_US.UTF-8
locale-coding-system: utf-8-unix
Major mode: Lisp Interaction
Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
eldoc-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
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t
Load-path shadows:
None found.
Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic 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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)
Memory information:
((conses 16 46301 9196)
(symbols 48 6004 1)
(strings 32 15750 1765)
(string-bytes 1 515528)
(vectors 16 10212)
(vector-slots 8 133109 13846)
(floats 8 21 45)
(intervals 56 310 11)
(buffers 1000 12))
In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
of 2020-05-19 built on felixonmars2
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20) of 2020-05-19
Mark set [2 times]
previous-line: Beginning of buffer [3 times]
Quit
Configured using:
'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
--localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
--with-modules 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt'
CPPFLAGS=-D_FORTIFY_SOURCE=2
LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'
Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD LCMS2
Important settings:
value of $LC_TIME: sr_RS.UTF-8
value of $LANG: en_US.UTF-8
locale-coding-system: utf-8-unix
Major mode: Lisp Interaction
Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
eldoc-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
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t
Load-path shadows:
None found.
Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic 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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)
Memory information:
((conses 16 95190 5384)
(symbols 48 20385 1)
(miscs 40 59 118)
(strings 32 28709 989)
(string-bytes 1 751949)
(vectors 16 13954)
(vector-slots 8 502510 11290)
(floats 8 50 104)
(intervals 56 224 0)
(buffers 992 11))
Best regards.
P.S.
Eli, Sorry for the second message.