[Webkit-unassigned] [Bug 77568] Different font glyphs for Hebrew/Yiddish not being displayed

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=77568





--- Comment #11 from Steve White <Stevan_White at hotmail.com>  2012-02-03 14:52:53 PST ---
Hi Kenichi, 

You asked
    What is the exact mean when you say "passing 'lang' attribute 
    to the underling libraries

Of course that depends on the underlying libraries.  But the 'lang' attribute is just a string from a set of standard language codes.  The only complication I can imagine here is that some APIs may be picky about the particular languge code standard they accept (but I don't know that.)

The DOM-level *intent* is to mark the text content of the entity as being of a different language than that of enclosing entities.  Just how that translates into calls to the underlying formatting software -- you would surely know better than I.  In principle it should be easy though (barring the ususual premature optimizations etc).

You also asked 
     "what OpenType feature should we use"

All OpenType features are ultimately activated by a list of 
      script( lang1, lang2, ... )
Where one of the languages may be the 'default' language.
The script is detected from the Unicode range of the input characters.
The language is (in the present case) derived from 'lang' tags.
The feature is activated if the Unicode of the input characters matches the script and the specified language matches one of the languages in the list.

So the answer is "this applies to all OpenType feature lookups".

In the Cyrillic example I provided, DejaVu Serif uses the 'locl' feature (this one feature is specifically intended to substitute individual glyphs based on language).
In the Hebrew example Ze'ev gave, FreeSans uses 'mark' and 'mkmk' positioning that depend upon language.  
I'm currently working on another font in which various Indic lookups ('pres', 'blwf', etc) depend upon language.

As to the specifics of API calls you need to make: you would know better than I.
I can only tell you: they are certainly present on each platform.

Let me know if I can provide further examples.  I have, e.g. some examples of pango-view making different output based upon language specification.

Cheers!

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