In a buffer that contains bidirectional text, setting
bidi-paragraph-direction to 'left-to-right aligns the RTL text with the
left margin like the LTR text; see the first sexp below and the top
buffer in the attached screenshot.
Another alternative to get this alignment is to leave
bidi-paragraph-direction at its default value of nil and use a space
display specification with a suitable value for the :align-to property,
but this requires a calculation that seems to depend at least on the
font used and the values of `window-width' and `string-width' for the
string used (or the corresponding pixel-width values); see the second
sexp below and the middle buffer in the attached screenshot.
It's also possible to avoid this calculation and use an :align-to value
of 0 in combination with setting bidi-paragraph-direction to
'left-to-right; see the third sexp below and the bottom buffer in the
attached screenshot. However, as the screenshot shows, this last
alternative breaks Arabic text shaping, at least for the fonts I tried
(Noto Naskh Arabic, DejaVu Sans and Amiri). If this is not an Emacs bug
but a limitation of the current display engine or a HarfBuzz bug,
perhaps it should be noted in etc/PROBLEMS.
(let* ((a "السّلام عليكم")
(b "Hello")
(buf (get-buffer-create "Test1")))
(with-current-buffer buf
(erase-buffer)
(setq bidi-paragraph-direction 'left-to-right)
(insert a "\n\n" b)
(switch-to-buffer buf)))
(let* ((a "السّلام عليكم")
(wa (+ (- (window-width) (string-width a)) 0.75))
(b "Hello")
(buf (get-buffer-create "Test2")))
(with-current-buffer buf
(erase-buffer)
(insert (propertize " " 'display `(space :align-to ,wa)) a "\n\n" b)
(switch-to-buffer buf)))
(let* ((a "السّلام عليكم")
(b "Hello")
(buf (get-buffer-create "Test3")))
(with-current-buffer buf
(erase-buffer)
(setq bidi-paragraph-direction 'left-to-right)
(insert (propertize " " 'display `(space :align-to 0)) a "\n\n" b)
(switch-to-buffer buf)))
Screenshot_2024-02-25_15-28-01.png
Description: PNG image
In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38, cairo version 1.18.0) of 2024-02-20 built on strobelfs2 Repository revision: d9afa1f30fdf9d00b447fea0a8343397333e172f Repository branch: master Windowing system distributor 'The X.Org Foundation', version 11.0.12101009 System Description: Linux From Scratch r12.0-112 Configured using: 'configure -C --with-xwidgets 'CFLAGS=-Og -g3' PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig' Configured features: ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM XWIDGETS GTK3 ZLIB
--- End Message ---