双方向テキスト

双方向テキスト(そうほうこうテキスト、英: bi-directional text)とは、右から左（RTL）と左から右（LTR）の2つの方向性を持つテキストです。

コンセプト

Text direction

in text editing, setting text direction changes how the program interacts with typed text including changes in text navigation, text selection, and text insertion.

Text alignment

text alignment only changes how text is displayed and styled.

Fake Bidi

a fake locale displaying completely reversed English sentences to mimic a RTL context. This helps developers who do not speak a RTL language to deal with RTL issues. For example:

This English sentence contains SDROW CIBARA EMOS and ends with English words.

Poor man's bidi mode

automatic visual text order right-to-left input in normal terminal.

Logical navigation

words are traversed as they are read.

Visual navigation

words are traversed as they are displayed. This GIF demonstrates the difference between the two.

Logical navigation is the correct way of navigation that programs should implement to fully support Bidi. Despite that, it would be preferable to have a switch between the two.

Unicode support

there are three main Unicode control characters: Wikipedia:RLM, Wikipedia:LRM, Wikipedia:ALM.

Bidirectional Algorithm

is the set of rules applied to display text in the correct order.

fribidi-git^AUR is an open source implementations of Bidi Algorithm. python-bidi^AUR is a python library for related functions.

サポート

In order for a program to fully support Bidi text, it must have:

Letter rendering (RTL)

able to correctly apply letter shaping and ligatures. See Complete Text Layout. This is often referred to shortly as RTL support.

Switch text alignment (Bidi)

E.g: Firefox Ctrl+Shift+X shortcut.

Logical navigation

in a RTL text, with RTL text alignment, arrow keys should not cause reversed navigation.

Tag	App	Date	RTL	Bidi	Nav	Notes
browser	chromium	2022-08-28	Yes	No	Yes	Chromium is the engine of ElectronJS. Fixing this should resolve Electron Apps too.
browser	firefox	2022-09-01	Yes	No	No
browser	qtwebbrowser	2022-11-01	Yes	No
browser	webkit	2022-11-01	Yes	No
editor	AbiWord	2007-12-06	Yes
editor	emacs	2019-06-31	Yes	No		With extension
editor	kate	2016-06-20	Yes	No
editor	LibreOffice		Yes	Yes	Yes	fully supported. Enabled using Complex Text Layout from settings.
editor	neovim	2014-04-17	No	No		see :set arabic
editor	texworks	2009-03-01	Yes	No
editor	vim	2015-08-19	No	No		see :set arabic
other	groff	2005-12-02	No	No	–
other	Wikipedia:HTML		Yes	Yes	Yes
other	latex		Yes	Yes	–	Using LuaTeX or XeLaTeX with polyglossia
other	wine	2002-04-21	Yes	No
terminal	alacritty	2017-07-15		No
terminal	dvtm	2019-10-12		No
terminal	gedit		Yes	No		For Gedit <= 2.1, workaround by extension.
terminal	irssi	2019-10-12		No
terminal	kitty	2019-11-01		No
terminal	konsole		Yes	No
terminal	libvte		Yes	No		including libvte-based like Gnome, sakura, xfce4...
terminal	mltermAUR		Yes	No
terminal	neatvi-gitAUR	2019-07-04		No
terminal	pymux	2019-10-12		No
terminal	qterminal		Yes	No
terminal	radare2	2015-02-03		No
terminal	tmux	2019-10-12		No		won't fix
terminal	wezterm	2021-05-11		No
terminal	xstAUR	2018-10-26		No

トラブルシューティング

Verify UTF-8 Encoding is properly configured first. Make sure you install the fonts corresponding to your language: Arabic, Persian, Hebrew. For some terminal, (bicon-git^AUR) is required to properly display Arabic and Hebrew text.

一時的な回避策

• Sublime text.

参照

内部リンク

• ロケール
• ローカリゼーション

外部リンク

• freedesktop specification for Bidi support: terminal.
• Comprehensive guide of RTL styling in HTML