[mpeg-OTspec] AHG conference call - Composite Fonts Requirements

John Hudson john at tiro.ca
Tue May 12 08:00:35 CEST 2009

>> Advanced Layout Features

>>   - Each component font should have code ranges and language tags  
>> identified, and will be used based on this information.

Before committing to agreement with MS and Adobe on layout 
non-interaction between component fonts, I just want to confirm that my 
understanding of intended code range and language tag behaviour is 
correct. The attached image shows text strings containing two different 
  scripts, typeset using two different fonts which, for purposes of this 
illustration represent two component fonts in a composite font. In this 
illustration, for clarity, I have set the two fonts in distinct colours, 
but one may presume them to represent text in a single colour. Language 
tagging is indicated.

There are two layout issues at work here. One is selection of an 
appropriate font for common punctuation characters adjacent to 
alphabetic characters, and hence correct kerning relationship between 
those glyphs. The other is the more complex selection of appropriate 
closing parenthesis to match opening parenthesis (as the illustration 
shows, there will definitely be cases in which this results in 
collisions between adjacent glyphs from different component fonts).

Given the language tagging illustrated in the graphic, is my 
understanding of the expected component font selection and layout correct?

I'm leaving aside, for now, posssible fallback behaviours, based on 
algorithms, if accurate language tagging is not applied.

Regards, John


Tiro Typeworks        www.tiro.com
Gulf Islands, BC      tiro at tiro.com

I'm like that Umberto Eco guy, but without
the writing.   -- anonymous caller
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