युनिकोड: Difference between revisions

Unicode, in intent, encodes the underlying [[character (computing)|charactercharacters]]s — [[grapheme]]s and grapheme-like units — rather than the variant [[glyph]]s (renderings) for such characters. In the case of [[Chinese character]]s, this sometimes leads to controversies over distinguishing the underlying character from its variant glyphs (see [[Han unification]]).

| {{CT-16}} | [[2001#March|March, 2001]] || {{CT-15}} | Unicode 3.1 || Added [[Mapping_of_Unicode_charactersMapping of Unicode characters|Supplementary Planes]] from ISO 10646-2, providing supplementary characters

UTF-16 is similar to UCS-2 but can include one or two 16-bit words in order to cover the supplementary characters (introduced from Unicode 3.1 onwards). UTF-16 is used by many APIs, often for upward compatibility with APIs that were developed when Unicode was UCS-2 based, or for compatibility with other APIs that use UTF-16. UTF-16 is the standard format for the [[Microsoft Windows|Windows]] API (though surrogate support is not enabled by default) and for the [[Java_Java (programming_languageprogramming language)|Java]] (J2SE 1.5 or higher) and .NET bytecode environments.

UCS-2 is an obsolete, 16-bit fixed-width encoding covering the [[Basic Multilingual Plane]] only. For characters in the Basic Multilingual Plane (16 bit range), UCS-2 and UTF-16 are identical. Therefore they can be considered as different implementation levels of the same encoding. The UCS-2 and UTF-16 encodings specify the Unicode [[Byte Order Mark]] (BOM) for use at the beginnings of text files. Some software developers have adopted it for other encodings, including UTF-8, which does not need an indication of byte order. In this case it attempts to mark the file as containing Unicode text. The BOM, code point U+FEFF has the important property of unambiguity, regardless of the Unicode encoding used. The units <code>FE</code> and <code>FF</code> never appear in [[UTF-8]]; U+FFFE (the result of byte-swapping U+FEFF) does not equate to a legal character, and U+FEFF conveys the zero-width no-break space (a character with no appearance and no effect other than preventing the formation of [[ligature (typography)|ligatureligatures]]s). The same character converted to UTF-8 becomes the byte sequence <code>EF BB BF</code>.

Unicode includes a mechanism for modifying character shape and so greatly extending the supported glyph repertoire. This covers the use of [[combining diacritical mark]]s. They get inserted after the main character (one can stack several combining diacritics over the same character). However, for reasons of compatibility, Unicode also includes a large quantity of [[precomposed character|pre-composed charactercharacters]]s. So in many cases, users have many ways of encoding the same character. To deal with this, Unicode provides the mechanism of [[canonical equivalence]].

[[As of 2004]], most software still cannot reliably handle many features not supported by older font formats, so combining characters generally will not work correctly. For example, {{unicode|ḗ}} (precomposed e with macron and acute above) and {{unicode|ḗ}} (e followed by the combining macron above and combining acute above) should be rendered identically, both appearing as an [[e]] with a [[macron]] and [[acute accent]], but in practice, their appearance can vary greatly across software applications. Similarly, [[dot (diacritic)|underdotunderdots]]s, as needed in the [[romanization]] of [[Indo-Aryan languages|Indic]], will often be placed incorrectly. As a workaround, Unicode characters that map to precomposed glyphs can be used for many such characters. The need for such alternatives inherits from the limitations of fonts and rendering technology, not weaknesses of Unicode itself.

* [[Uniscribe]] — [[Microsoft Windows|Windows]]

* [[Apple Type Services for Unicode Imaging]] — new engine for [[Apple Macintosh|Macintosh]]

* [[WorldScript]] — old engine for [[Apple Macintosh|Macintosh]]

* [[Pango]] — [[Open Source]], used by [[GTK+]] (and hence [[GNOME]])

* [[International Components for Unicode|ICU Layout Engine]] — Open Source

* [[Graphite (SIL)|Graphite]] — (Open Source renderer from [[SIL International|SIL]])

* [[Qt (toolkit)|Scribe]] — Open Source renderer from [[Trolltech]]

In the [[Vim (text editor)|Vim]] text editor, Unicode characters can be entered by pressing CTRL-V and then entering a key combination. For more information, type "<code>:help i_CTRL-V_digit</code>" in Vim. (Note that the entered text will be Unicode only if the current encoding is set to UTF-8 or another Unicode encoding; type "<code>:help encoding</code>" in Vim for details.) Many Unicode characters can also be entered using [[Digraph (computing)|digraphdigraphs]]s; a table of such characters and their corresponding digraphs can be obtained using the "<code>:digraphs</code>" command (again provided the current encoding is set to Unicode).

* [http://quickkeydotnet.sourceforge.net/ Quick Key] (Open Source)

* [http://cjb.ie/u.php Lightweight Unicode Map/Picker] (In-browser character map; operating-system independent. Open Source)

* [http://www.ergonis.com/products/popchar/ PopChar Demo Version]

[[Imageकिपा:Unicodeconsortium_book4.jpg|thumb|right|The Unicode Standard, Version 4.0]]

** Insert characters instantly with [http://quickkeydotnet.sourceforge.net/ Quick Key Character Grid].

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