Fonts and Canonical Equivalence

[Richard Wordingham via Unicode]

On Sat, 10 Aug 2019 16:37:48 +0100
Andrew West via Unicode <unicode at unicode.org> wrote:

> On Sat, 10 Aug 2019 at 15:46, Richard Wordingham via Unicode
> <unicode at unicode.org> wrote:

> > Does vowel above before vowel below yield a dotted circle?  
> 
> Yes. Attached are screenshots for two real world examples, one which
> is logically spelled as i + u, and one as u + i:
> 
> 1. ཉིུ <0F49 0F72 0F74> [nyiu] as a contraction for ཉི་ཤུ [nyi shu]
> "twenty"
> 
> 2. བཅིུག <0F56 0F45 0F74 0F72 0F42> [bcuig] as a contraction for
> བཅུ་གཅིག [bcu gcig] "eleven"

Thanks for the clarification.  I must have done something wrong when I
tried to break Tibetan rendering by an above-below sequence - unless MS
Edge denormalises Tibetan text so that it will render.

However, we may be able to redress the balance between the renderers by
inserting CGJ between the vowels to preserve the order when the strings
are copied:

nyiu ཉི͏ུ 0F49 0F72 034F 0F74

bcuig བཅུ͏ིག  0F56 0F45 0F74 034F 0F72 0F42

On my machine they display without dotted circles in Claws-Mail and
LibreOffice, but I may be using too old a version of HarfBuzz.  However,
the ligaturing is missing in _nyiu_ with CGJ. LibreOffice at least is
using Tibetan Machine Uni.  However, in a snapshot of HarfBuzz I pulled
in the past few days, both were rendered with dotted circles. This issue
is apparently being worked on - 
(https://github.com/harfbuzz/harfbuzz/issues/483).

The forms without CGJ render fine in the two applications

Richard.