[XeTeX] Contextual shaping

[Zdenek Wagner]

2013/11/27 Simon Cozens <simon at simon-cozens.org>:
> This is possibly a daft question, but...
>
> In traditional TeX, character tokens are processed and put into boxes
> individually, with fairly primitive ligature tables. Obviously XeTeX doesn't
> do this, using Harfbuzz (or ICU or whatever) to do the shaping and layout.
>
> My question is, if you're not "showing" individual characters to the shaping
> engine for it to consider, what defines how big a string of characters to
> shape at a time? Does XeTeX break at the "word" level and then shape a word,
> and if so what defines a word? (Chinese has no word breaks!) Or does it
> shape an entire paragraph of text at a time (!) and then box up the glyphs
> individually? Or...?
>
I am not an expert but shaping can be changed within a pragraph. The
following file produces the attached PDF:

\documentclass{article}
\usepackage{fontspec,polyglossia}
\setotherlanguages{hindi,sanskrit}
\newfontfamily\hindifont[Language=Hindi,Script=Devanagari,Mapping=velthuis]{FreeSerif}
\newfontfamily\sanskritfont[Language=Sanskrit,Script=Devanagari,Mapping=velthuis]{FreeSerif}
\def\shakti{"sakti}
\begin{document}

Hindi: \texthindi{\shakti}, Sanskrit: \textsanskrit{\shakti}

\end{document}


> (I've tried starting at layoutChars in XeTeXLayoutInterface.cpp and working
> backwards but I can't understand where I end up: measure_native_node shapes
> a node, but what's a node?)
>
>
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-- 
Zdeněk Wagner
http://hroch486.icpf.cas.cz/wagner/
http://icebearsoft.euweb.cz
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