[EversonMono] Everson Mono: mac os: mozilla mac os x 10.5 yiddish hebrew test

John Hudson tiro at tiro.com
Fri Mar 13 04:26:18 GMT 2009

> do you have
> any theory off the top of your head as to why Ezra SIL horizontal placement
> of vowel points (nonspacing marks) is mostly wrong on Mac OS X?

See previous message for the general answer. Here is the more specific one:

Before Microsoft began to develop OpenType technology and layout, they 
had a crude Hebrew text engine that would position marks relative to 
letters by aligning the zero-width mark on the centre of the letter. 
Since the majority of Hebrew marks are horizontally centred on the 
letter, this crude mechanism worked reasonably well for most 
combinations. Obviously it didn't work for letters like dalet and resh 
that take marks under the right vertical, but this was an accepted 
limitation of this primitive mechanism. It was to address such 
limitations that the much more sophisticated mechanisms of OpenType 
glyph substitution and positioning were introduced (c.1997)

Because of this legacy mechanism, the tendency of people producing 
OpenType Hebrew fonts primarily targeted at Windows -- such as Ralph 
Hancock, maker of the Ezra SIL SR font, with whom I collaborated on 
working out the Hebrew glyph processing intelligence in that font and in 
my SBL Hebrew -- has been to position marks centred on the zero-width, 
rather than, say, offset to the right so that, in the absence of OTL 
support, they sit roughly somewhere under the preceding letter. This 
means that if a Windows user has not updated his operating system to 
Windows 2000 or later (yup, there are still Windows ME users out there), 
the new fonts will still display as well as possible using the old, 
crude mechanism.

Since Mac OS never had the same older mechanism, such fonts display 
incorrectly in the absence of OTL support: the marks centred on their 
zero-widths will display between the preceding letter and the following 
one, as seen in your PDF.


PS. I don't know all the fonts spec'd in your test document. It is 
possible that some of them include Apple's AAT tables, which provide 
some similar functionality to OpenType but only on the Mac and not in 
all applications. It is possible that Firefox makes use of ATSUI, the 
Apple system resource for Unicode text, and so might display AAT fonts 
better than others.

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