In the OpenType model, a distinction is made between font-specific behaviours and font-neutral script behaviours. OpenType Layout tables were designed to deal with only font-specific details, leaving it to OTL client software to handle anything that is font-neutral.
Re-ordering of prepended Buginese vowel /e/ is a font-neutral behaviour. More generally, re-ordering in Brahmi-derived scripts is considered a font-neutral behaviour, and OpenType Layout does not include means to describe the re-ordering of characters. (You could fake things out by creating ligature glyphs for entire syllables, but that isn't generally recommended. So, if you're not seeing Buginese script text rendering as expected specifically wrt the re-ordering issue, that's an issue with the rendering software--a bug if the software claims to support Buginese, a limitation if it doesn't. Peter -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of verdy_p Sent: Saturday, July 23, 2011 9:13 AM To: Unicode Mailing List Subject: Prepending vowel exception in Lontara/Buginese script ? 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. 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 ? 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, or should Unicode be modified to inclide the "prepended vowel" exception also for Buginese, and so the default grapheme boundaries modified as well, and the Unicode 6.0 chart modified too for U+1A19 ? -- Philippe.
