Re: Fallback for Sinhala Consonant Clusters

Hi Richard,

On 15/10/18 6:53 pm, Richard Wordingham via Unicode wrote:
> On Mon, 15 Oct 2018 01:55:24 +1100
> Harshula via Unicode <unicode_at_unicode.org> wrote:
>
>> 3) However, what you have observed is an issue with *explicit*
>> conjunct creation. After the segmentation is completed, the
>> layout/shaping engine needs to first check if there is a
>> corresponding lookup for the explicit conjunct, if not, then it needs
>> to remove the ZWJ and redo the segmentation and lookup(s). Perhaps
>> that is not happening in Harfbuzz.
>
> This indeed seems to be the problem with HarfBuzz and with Windows 7
> Uniscribe. Curiously, they almost adopt this behaviour when touching
> letters are not available. (The ZWJ seems not to be completely removed
> - in HarfBuzz at least it can result in the al-lakuna not interacting
> properly with the base character.)
>
> But where is this usually useful behaviour specified?
>
> 1. There may be nothing but time and money to stop fallbacks being
> built into the font. For example, what prohibits the rendering of a
> conjunct falling back to touching letters or a missing glyph symbol?

I had not considered the missing glyph symbol. Perhaps that is the most
accurate solution when a font is missing a glyph during an *explicit*
conjunct lookup.

Note, touching letters are formed by <ZWJ><AL-LAKUNA>, so they should
not be displayed as a fallback for <AL-LAKUNA><ZWJ> conjuncts.

cya,
#
Received on Mon Oct 15 2018 - 10:48:06 CDT