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Encodings and Regimes - Old Content (view source)
Revision as of 07:09, 27 December 2004
, 07:09, 27 December 2004no edit summary
==Typesetting in UTF==
Use <texcode>\enableregime[utf]</texcode> in order to be able to typeset in unicode under ConTeXt.
==How it works?==
'''Robert Ermers''' and '''Adam Lindsay'' provided a helpful explanation of how Characters are constructed in LaTeX and ConTeXt (in some discussion on the mailing list):
You know that all characters in a font have a number. If you type <code>a</code>, the font mechanism makes sure that you see an <context>a</context>. In reality the font shows you the character that is put on the numerical position of <code>a</code>. In the font dingbats for example, the character on that position is not an <context>a</context>, but a symbol.
===In Latex=== the combination <code>\"{a}</code> can mean two things:
* in most fonts: show the charachter on the a given numerical position, which means that there is one character <context>\"{a}</context>.
* in some other fonts <code>\"{a}</code> means: combine <code>"</code> with <code>a</code> and make an <context>\"{a}</context>. This means that <code>"</code> is combined with the character on the numerical position of <code>a</code>. TeX does this very well and thus construes very acceptable diacritical signs like <code>\"{q}</code>, <code>\d{o}</code>, <code>\v{o}</code>, which do not exist in regular fonts.
If you have a font which contains <code>\"{q}</code>, <code>\d{o}</code> or some other special characters, you may instruct TeX not to create the character, but rather to show the contents of a given numerical position in that font. That's what the .enc and .fd files under Latex are for.
That's also the reason there are, or used to be, special fonts for Polish an Czech and other languages: they contain predefined characters in one single numerical position, e.g. <code>\v{s}</code> and <code>\v{c}</code> that TeX does not have to create anew from two signs.
===In ConTeXt=== the combination \"{a} means one thing: \adiaeresis (see enco-acc). This \adiaeresis can mean one of two things, depending on the encoding:
* Numerical position, or
* The fallback case (defined in <b>enco-def</b>), where a diaeresis/umlaut is placed atop an 'a' glyph. Hyphenation implications as Hans described.
The interesting/helpful thing about ConTeXt is that internally, that glyph is given a consistent name, no matter how it is input or output. So, if you type <code>ä</code> in your given input regime, and that encoding is properly set, that numerical <code>ä</code> (e.g., character <code>#228</code> in the windows regime) is mapped to <code>\adiaeresis</code>.
Wanna know what happens in UTF-8? Here's my 'simplified' explanation:
In a UTF-8 bytestream, that character <context>\"{a}</context> is signified by two bytes:
<code>0xC3</code>, <code>0xA4</code>. That first byte triggers a conversion of both bytes into two
different bytes, the actual Unicode number, <code>0x00 0xE4</code> (or: <code>0, 228</code>). ConTeXt then looks into internal hashes set up (in this case, the <b>unic-000</b> vector), looks at the 228<sup>th</sup> element, and sees that it's <code>\adiaeresis</code>. Things then proceed as normal. :)
(It's also interesting to note that for PostScript and TrueType fonts, that number > name > number (glyph) mapping happens yet again in the driver. But all that is outside of TeX proper, so to say any more would be confusing.)
Use <texcode>\enableregime[utf]</texcode> in order to be able to typeset in unicode under ConTeXt.
==How it works?==
'''Robert Ermers''' and '''Adam Lindsay'' provided a helpful explanation of how Characters are constructed in LaTeX and ConTeXt (in some discussion on the mailing list):
You know that all characters in a font have a number. If you type <code>a</code>, the font mechanism makes sure that you see an <context>a</context>. In reality the font shows you the character that is put on the numerical position of <code>a</code>. In the font dingbats for example, the character on that position is not an <context>a</context>, but a symbol.
===In Latex=== the combination <code>\"{a}</code> can mean two things:
* in most fonts: show the charachter on the a given numerical position, which means that there is one character <context>\"{a}</context>.
* in some other fonts <code>\"{a}</code> means: combine <code>"</code> with <code>a</code> and make an <context>\"{a}</context>. This means that <code>"</code> is combined with the character on the numerical position of <code>a</code>. TeX does this very well and thus construes very acceptable diacritical signs like <code>\"{q}</code>, <code>\d{o}</code>, <code>\v{o}</code>, which do not exist in regular fonts.
If you have a font which contains <code>\"{q}</code>, <code>\d{o}</code> or some other special characters, you may instruct TeX not to create the character, but rather to show the contents of a given numerical position in that font. That's what the .enc and .fd files under Latex are for.
That's also the reason there are, or used to be, special fonts for Polish an Czech and other languages: they contain predefined characters in one single numerical position, e.g. <code>\v{s}</code> and <code>\v{c}</code> that TeX does not have to create anew from two signs.
===In ConTeXt=== the combination \"{a} means one thing: \adiaeresis (see enco-acc). This \adiaeresis can mean one of two things, depending on the encoding:
* Numerical position, or
* The fallback case (defined in <b>enco-def</b>), where a diaeresis/umlaut is placed atop an 'a' glyph. Hyphenation implications as Hans described.
The interesting/helpful thing about ConTeXt is that internally, that glyph is given a consistent name, no matter how it is input or output. So, if you type <code>ä</code> in your given input regime, and that encoding is properly set, that numerical <code>ä</code> (e.g., character <code>#228</code> in the windows regime) is mapped to <code>\adiaeresis</code>.
Wanna know what happens in UTF-8? Here's my 'simplified' explanation:
In a UTF-8 bytestream, that character <context>\"{a}</context> is signified by two bytes:
<code>0xC3</code>, <code>0xA4</code>. That first byte triggers a conversion of both bytes into two
different bytes, the actual Unicode number, <code>0x00 0xE4</code> (or: <code>0, 228</code>). ConTeXt then looks into internal hashes set up (in this case, the <b>unic-000</b> vector), looks at the 228<sup>th</sup> element, and sees that it's <code>\adiaeresis</code>. Things then proceed as normal. :)
(It's also interesting to note that for PostScript and TrueType fonts, that number > name > number (glyph) mapping happens yet again in the driver. But all that is outside of TeX proper, so to say any more would be confusing.)