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

[F Wolff <friedel@xxxxxxxxxxxxxxxx>]

Op Dinsdag 2008-01-01 skryf David Rowe:

Hallo David

...

> In order for a Unicode font to support dynamic composition, the font 
> must contain the necessary information and there must be software that 
> can use that information to correctly position the diacritic with the 
> base character. Under Windows, the Uniscribe processor provides the 
> software support necessary for an application to render combining 
> diacritics (provided the application knows to use the Uniscribe 
> processor). For example, Word 2003 running on Windows XP can render 
> U+025B U+0303 U+0300 (epsilon with the tilde combining diacritic on top 
> of the epsilon and the grave combining diacritic stacked on top of the 
> tilde) provided that a font (such as Doulos SIL) is used which contains 
> the information for placing these diacritics.

It is my understanding that OpenOffice.org running on Windows XP will
also use Uniscribe, perhaps selectively.

> 
> 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. I have created such fonts by using SIL's Encore Font system 
> (originally designed for creating custom 8-bit fonts, but also capable 
> of creating Unicode fonts) then adding the substitution information with 
> VOLT. The Microsoft Uniscribe processor is still needed to do the 
> substitution, so this solution should work with Word 2003 on Windows XP.
> 
> My need for a sans-serif font and a mono-spaced font was the motivation 
> for creating fonts that support only a subset of base character / 
> diacritic combinations. (SIL Doulos is a serif, variable width font.) 
> When a sans-serif Unicode font that supports all the needed characters 
> becomes available, then it can be used instead of my custom font with no 
> change in the text of the document, just a change of font.

I am curious about this: Does .DejaVu not cover everything you need? Are
there features missing in terms of the diacritic placing? .DejaVu
contains .serif, .sansserif and .sansmono faces. I would really like to
know if there are shortcomings in this area, as this is quite important
for several locales in Africa, I think. I was under the impression that
it already works reasonably well for Vietnamese, which contains a lot of
these combinations.

> 
> If the text were to contain the sequence U+025B U+0300 U+0303 (epsilon 
> with grave and tilde), then the Doulos SIL font will render it correctly 
> (with the tilde on top of the grave on top of the epsilon) whereas the 
> fonts I created will not since that particular combination doesn't occur 
> as a precomposed character (because none of the languages that this font 
> was intended to support uses that combination).
> 
> I don't know what the situation is for Mac. 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.
> 
> David Rowe
> SIL Togo-Benin

On .Linux such rendering is performed by .Pango (part of .GTK
and .GNOME) or by the .Qt widget set. This means that most applications
support this automatically to the level that the underlying software
(.Pango or .Qt) supports it, and don't really need to "support" it in
themselves, except perhaps for .Unicode normalisation (I'm not sure
about this).

Keep well
Friedel Wolff