Re: [A12n-Collab] Re: 5 categories of African orthographies (Latin)

[John Hudson <tiro@xxxxxxxx>]

David Rowe wrote:

> It is also possible to create a font that provides support for a subset 
> of base character / diacritic combinations by including all the needed 
> combinations as precomposed characters in the Private Use Area, and then 
> adding substitution information (using Microsoft's VOLT) that will, for 
> example, substitute the precomposed epsilon+tilde+grave character which 
> I put at U+E04F when the combination U+025B U+0303 U+0300 is found in 
> the text. 
Note that such glyphs do not need to have PUA codepoint: they can be unencoded glyphs, 
accessed via the OpenType Layout substitution lookups you describe.
> I don't know what the situation is for Mac. 
Apple are gradually adding support for OpenType Layout, but they have a ways to go and do 
not, as yet, support dynamic mark positioning.
Apple also have their own font layout intelligence -- AAT -- which is supported in their 
own apps. It is possible to make a font that supports both OTL and AAT, but very few 
people have bothered to do so, since OpenType clearly has the dominant market share.
> For Linux, there exist 
> already, or are in development, ways to render Unicode text which uses 
> combining diacritics. The font needs to include the necessary 
> information and the application and the operating system need to provide 
> the software support for the rendering.
Yes, for instance the ICU layout engine, used in a lot of open source software, which 
makes use of OpenType Layout.
John Hudson