Fonts and Canonical Equivalence

[Andrew West via Unicode]

On Sat, 10 Aug 2019 at 08:29, Richard Wordingham via Unicode
<unicode at unicode.org> wrote:
>
> There are similar issues with Tibetan; some fonts do not work properly
> if a vowel below (ccc=132) is separated from the base of the
> consonant stack by a vowel above (ccc=130).

It's not that the fonts don't work, it's that some the rendering
engines do not apply the OpenType features in the font that support
both sequences of vowels (vowel-above followed by vowel-below, and
vowel-below followed by vowel-above). Just retested on Windows 10 with
a Tibetan font that supports both sequences of vowels, and both
sequences display correctly under Harfbuzz (as expected), but only
vowel-below followed by vowel-above displays correctly when using
built-in Windows rendering.

It is very frustrating that Windows cannot correctly support the
display of Tibetan in normalized form, yet Harfbuzz does not have any
problems. Personally, I think USE is a failed experiment, and I wish
Microsoft would simply adopt Harfbuzz as the default rendering engine.

Andrew