Prepending vowel exception in Lontara/Buginese script ?

From: verdy_p <verdy_p_at_wanadoo.fr>
>
> If I look in the Unicode 6.0 charts for the Buginese script, I see that
> vowel /e/ (U+1A19) is prepended visually on the left of the base consonnant
> to which it applies. This should mean that the vowel has to be encoded
> ilogically in texts AFTER the base consonnant to which it applies.

It actually IS encoded logically, just not visually. Logically, the E comes after after the consonant sound. That's the reality that Unicode reflects. The fact that the script prepends this vowel mark before the consonant doesn't change that it logically comes after the consonant.

> However, I have tested all fonts available on the web for this script, and
> none of them contain the necessary OpenType substitution feature needed to
> make the logical-to-visual reordering.
>
> Is this a bug of these fonts (most of them are TrueType only, not OpenType
> with a reordering feature like those used in other Indic scripts, but built
> like basic TrueType fonts for Thai, Lao and Tai Viet scripts, that are the
> only scripts for which Unicode has defined the "Prepended Vowel" exception)?
>
> Or is is a bug/limitation of text renderers ?

If a script has prepended vowels, the fonts should have OpenType features enabled. It is absolutely a bug with the fonts.

> I note for example that Chrome correctly uses Unicode 6.0 default grapheme
> cluster boundaries, when editing and selecting in Lontara text (written in
> Biginese or Makassar languages), so that the vowel will be selected/deleted
> logically along with the base character encoded before it (for example a
> space or punctuation, or even a HTML syntax character). But if I use this
> browser to display Lontara text, the vowel /e/ is still shown with the
> diacritic on the right of the base consonnant (or dotted circle symbol),
> meaning that the text is garbled when I use any one of those available fonts.
>
> All texts in Makassar or Buginese I have found, encoded in Unicode, seem to
> assume the visual order (i.e. the same "prepended vowel" exception as in
> Thai and Lao). Given the geographical area where the Lontara script is
> mostly used (Indonesia and Thailand), it seems quite logical that text
> authors assumed this exception to the logical encoding order.
>
> What can be done? Should the fonts be corrected to include the OpenType
> feature,

Yes.

> or should Unicode be modified to inclide the "prepended vowel"
> exception

No.

> also for Buginese, and so the default grapheme boundaries modified
> as well, and the Unicode 6.0 chart modified too for U+1A19 ?

No.

> -- Philippe.

Van
Received on Sat Jul 23 2011 - 19:05:37 CDT