Duospaced font
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A duospaced font (also called a duospace font) is a fixed-width font whose letters and characters occupy either of two integer multiples of a specified, fixed horizontal space. Traditionally, this means either a single or double character width, although the term has also been applied to fonts using fixed character widths with another simple ratio between them. These dual character widths are also referred to as ''half-width'' and ''full-width'', where a full-width character occupies double the width of a half-width character. This contrasts with variable-width fonts, where the letters and spacings have more than two different widths. And, unlike
monospaced font A monospaced font, also called a fixed-pitch, fixed-width, or non-proportional font, is a font whose letters and characters each occupy the same amount of horizontal space. This contrasts with variable-width fonts, where the letters and spac ...
s, this means a character can occupy up to two effective character widths instead of a single character width. This extra horizontal space allows for the accommodation of wider glyphs, such as large ideographs, that cannot reasonably fit into the single character width of strictly uniform, monospaced font.


In CJK typography

The idea of a "duospaced" font came from East Asian typography, where the local scripts of
CJK characters In internationalization, CJK characters is a collective term for the Chinese, Japanese, and Korean languages, all of which include Chinese characters and derivatives in their writing systems, sometimes paired with other scripts. Collectively, th ...
simply cannot fit into a narrow column used in Latin fixed-pitch fonts. Note that this "duospace" name is mostly a historical (c. 1990) Western distinction; Asian typefaces with such characteristics simply call themselves "monospaced" or "fixed pitch". CJK monospace fonts typically include
halfwidth and fullwidth forms In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK: 半角) characters. Unlik ...
of characters that provide different widths for typesetting. In addition to East Asian characters and such forms, it is common for other technical and
pictographic A pictogram, also called a pictogramme, pictograph, or simply picto, and in computer usage an icon, is a graphic symbol that conveys its meaning through its pictorial resemblance to a physical object. Pictographs are often used in writing and ...
symbols to become ''duospaced'' in some East Asian fonts, a phenomenon known as "ambiguous width". It is a common pitfall for Western programmers to neglect support for such fonts: * Terminal applications may have misaligned output due to assuming all character "pitch" to be 1 column wide. The function, originally part of
POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming inter ...
, is available for querying the width of characters. * Qt has a bug where it fails to list CJK monospaced fonts because the underlying
fontconfig Fontconfig (or fontconfig) is a free software program library designed to provide configuration, enumeration and substitution of fonts to other programs. Fontconfig was originally written and maintained by Keith Packard, and is currently maintai ...
defined "monospace" as "fixed-pitch" fonts. With the exception of some Japanese monospace fonts like Source Han Code JP, where a 1.5× width is used as the ideograph width, almost all CJK monospace fonts use 2× as the ideograph width. (In the case of the
Korean language Korean ( South Korean: , ''hangugeo''; North Korean: , ''chosŏnmal'') is the native language for about 80 million people, mostly of Korean descent. It is the official and national language of both North Korea and South Korea (geographic ...
, Hangul characters which are usually slightly narrower than the ideographs are made to match them.) Some CJK monospace fonts with two or more widths are: * Andale Duospace WT *
GNU Unifont GNU Unifont is a free Unicode bitmap font using an intermediate bitmapped font format created by Roman Czyborra. The main Unifont covers all of the Basic Multilingual Plane (BMP). The "upper" companion covers significant parts of the Supplementa ...
(pan-character set) * Migu 1M, Migu 2M * Monotype Sans Duospace WT * Thorndale Duospace WT * WorldType Sans Duo, WorldType Serif Duo * Source Han Code JP (1.5×) * WenQuanYi Micro Hei Mono, WenQuanYi Zen Hei Mono


In Western typography

Western duospaced fonts are similar in purpose to CJK duospaced fonts, but they are much rarer and less supported. The idea seems to be limited to an iA Writer typeface where the latin characters have 1.5× widths, so that they retain the traditional letter shape better.


See also

*
Halfwidth and fullwidth forms In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK: 半角) characters. Unlik ...
*
Half-width kana are katakana characters displayed compressed at half their normal width (a 1:2 aspect ratio), instead of the usual square (1:1) aspect ratio. For example, the usual (full-width) form of the katakana ''ka'' is カ while the half-width form is カ. ...


Notes


References

{{Reflist Typesetting