- From: John Hudson <tiro@tiro.com>
- Date: Fri, 15 Aug 2014 12:06:51 -0700
- To: "Tab Atkins Jr." <jackalmage@gmail.com>, John Daggett <jdaggett@mozilla.com>
- CC: fantasai <fantasai.lists@inkedblade.net>, WWW International <www-international@w3.org>, www-style list <www-style@w3.org>
> Note: This means that color changes, font changes, letterspacing >changes, etc. have no effect on shaping. Shaping might not result >in the glyphs joining correctly, but will nonetheless choose the >correct form of the letter (initial, medial, final, isolated). Further to what John D and Glenn have written with regard to this: Whether a change in font results in a change in character shaping will depend on whether the desired shaping is affected by discrete layout features applied based on character level analysis (broadly speaking, the OpenType Layout model for basic Arabic shaping and *some* aspects of Indic cluster shaping), or is instead affected at the glyph level using contextual substitutions (broadly speaking, the AAT/Graphite model). So, for example, an Arabic medial letter form can be displayed by a typical Arabic OpenType font using character string analysis, even if there is a change in font between this letter and the next. The two resulting glyphs won't join nicely, but they should take their respective basic joining forms according to the Unicode joining behaviour model. In contrast, an AAT font that uses glyph string analysis to affect state changes seems almost guaranteed to break shaping when the font changes in mid-string. The reality of most complex script fonts, though -- even those following the MS OpenType script specifications --, is that they utilise a mixture of basic shaping associated with discrete features applied by layout engines according to character string analysis and glyph-level contextual substitutions. J.
Received on Friday, 15 August 2014 19:07:23 UTC