[EversonMono] everson mono - bugs with Yiddish (Hebrew) with dagesh

John Hudson tiro at tiro.com
Tue Mar 3 14:45:18 GMT 2009


Michael wrote:

>> 1. The layout engine performs a character-level substitution of the 
>> precomposed letter+dagesh from the Alphabetic Presentation Forms block 
>> in Unicode. This is most likely done in a buffered state during 
>> display, not affecting the stored characters string.

> That would be OS-specific or application-specific, I guess?

Yes.

> Yes, by pointing Baseletter + combining Dagesh to the Alphabetic 
> Presentation forms glyphs. I have now updated Everson Mono to do this in 
> two ways. First, I checked to see that my mappings from Base + Diacritic 
> to Alphabetic Presentation forms were correct. Then, I duplicated this 
> GSUB feature so that the font contains both <ccmp> and <liga> (Why? 
> Because some apps render <liga> but ignore <ccmp>.)

That makes sense.

> Ah, yes, this witchcraft. I don't really know how to do this. Does 
> FontLab even support it? I know there's this VOLT thing out there, but 
> as I work on the Mac OS I find myself curiously unmotivated to try to 
> deal with it. I know... I lag behind... but I really do prefer font 
> tools made for humans, rather than for programmers. ;-)

Ironically, this is one of the reasons why I prefer VOLT to FL for 
OpenType Layout: it is a visual tool rather than code-based like the FDK 
syntax used in FontLab. I don't need to do any programming in VOLT: just 
enter lists of inputs and outputs for GSUB and numbers for GPOS positioning.

> "Layout engines" residing... where? Do they have names? I know that on 
> the Mac OS some apps -- even apps shipped by Apple do better than 
> others, but there's never any end-user info as to what "engine" 
> different apps use.

Adobe use their own layout engines, of which they basically have two: 
the Adobe Composer and the World-Ready Composer. The latter is fairly 
new, and is the default engine only in the Middle East version of CS4 
apps. The World-Ready Composer is very nice: even supports Indic scripts.

Most Windows apps use the Uniscribe layout engine. There is a 
system-level Uniscribe, and some MS apps also ship with their own 
version which can provide additional script support between OS releases.

Apple have their ATSUI engine, but for the most part this has not 
supported OT fonts for complex scripts.

JH




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