You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
66 lines
3.1 KiB
66 lines
3.1 KiB
3 years ago
|
### Javascript porting of Markus Kuhn's wcwidth() implementation
|
||
|
|
|
||
|
|
The following explanation comes from the original C implementation:
|
||
|
|
|
||
|
|
This is an implementation of wcwidth() and wcswidth() (defined in
|
||
|
|
IEEE Std 1002.1-2001) for Unicode.
|
||
|
|
|
||
|
|
http://www.opengroup.org/onlinepubs/007904975/functions/wcwidth.html
|
||
|
|
http://www.opengroup.org/onlinepubs/007904975/functions/wcswidth.html
|
||
|
|
|
||
|
|
In fixed-width output devices, Latin characters all occupy a single
|
||
|
|
"cell" position of equal width, whereas ideographic CJK characters
|
||
|
|
occupy two such cells. Interoperability between terminal-line
|
||
|
|
applications and (teletype-style) character terminals using the
|
||
|
|
UTF-8 encoding requires agreement on which character should advance
|
||
|
|
the cursor by how many cell positions. No established formal
|
||
|
|
standards exist at present on which Unicode character shall occupy
|
||
|
|
how many cell positions on character terminals. These routines are
|
||
|
|
a first attempt of defining such behavior based on simple rules
|
||
|
|
applied to data provided by the Unicode Consortium.
|
||
|
|
|
||
|
|
For some graphical characters, the Unicode standard explicitly
|
||
|
|
defines a character-cell width via the definition of the East Asian
|
||
|
|
FullWidth (F), Wide (W), Half-width (H), and Narrow (Na) classes.
|
||
|
|
In all these cases, there is no ambiguity about which width a
|
||
|
|
terminal shall use. For characters in the East Asian Ambiguous (A)
|
||
|
|
class, the width choice depends purely on a preference of backward
|
||
|
|
compatibility with either historic CJK or Western practice.
|
||
|
|
Choosing single-width for these characters is easy to justify as
|
||
|
|
the appropriate long-term solution, as the CJK practice of
|
||
|
|
displaying these characters as double-width comes from historic
|
||
|
|
implementation simplicity (8-bit encoded characters were displayed
|
||
|
|
single-width and 16-bit ones double-width, even for Greek,
|
||
|
|
Cyrillic, etc.) and not any typographic considerations.
|
||
|
|
|
||
|
|
Much less clear is the choice of width for the Not East Asian
|
||
|
|
(Neutral) class. Existing practice does not dictate a width for any
|
||
|
|
of these characters. It would nevertheless make sense
|
||
|
|
typographically to allocate two character cells to characters such
|
||
|
|
as for instance EM SPACE or VOLUME INTEGRAL, which cannot be
|
||
|
|
represented adequately with a single-width glyph. The following
|
||
|
|
routines at present merely assign a single-cell width to all
|
||
|
|
neutral characters, in the interest of simplicity. This is not
|
||
|
|
entirely satisfactory and should be reconsidered before
|
||
|
|
establishing a formal standard in this area. At the moment, the
|
||
|
|
decision which Not East Asian (Neutral) characters should be
|
||
|
|
represented by double-width glyphs cannot yet be answered by
|
||
|
|
applying a simple rule from the Unicode database content. Setting
|
||
|
|
up a proper standard for the behavior of UTF-8 character terminals
|
||
|
|
will require a careful analysis not only of each Unicode character,
|
||
|
|
but also of each presentation form, something the author of these
|
||
|
|
routines has avoided to do so far.
|
||
|
|
|
||
|
|
http://www.unicode.org/unicode/reports/tr11/
|
||
|
|
|
||
|
|
Markus Kuhn -- 2007-05-26 (Unicode 5.0)
|
||
|
|
|
||
|
|
Permission to use, copy, modify, and distribute this software
|
||
|
|
for any purpose and without fee is hereby granted. The author
|
||
|
|
disclaims all warranties with regard to this software.
|
||
|
|
|
||
|
|
Latest version: http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
|
||
|
|
|
||
|
|
|
||
|
|
|