[XeTeX] On combining diacritics again

Jonathan Kew jonathan_kew at sil.org
Fri Jan 20 13:26:38 CET 2006

One more follow-up on this, just to illustrate the various behaviors.  
The attached screenshot shows the exact same Unicode text sequence  
rendered in three different ways: (1) without any layout tables in  
the font (so the diacritics just overstrike); (2) with full OpenType  
tables present, so they stack properly; and (3) via the Cocoa text  
system without layout tables, so we get Cocoa's default stacking  

With most fonts, assuming the characters are present at all, you'll  
see (1) in XeTeX (because few fonts have the layout tables needed),  
and you'll see (3) in most Cocoa applications. The correct appearance  
is (2), but requires both a font that has the proper tables, and an  
application that knows how to use them. (This example is, of course,  
XeTeX using Charis SIL.)

(Note that as of Mac OS 10.4, ATSUI and Cocoa Text *does* know how to  
use some OpenType layout features, if present in the font; the  
implementation is incomplete, however.)

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