Dear Richard and Peter,
apologies for the lack of clarity. Let me try to explain below.
On 2018-08-29 01:13, WORDINGHAM RICHARD via Unicode wrote:
On 27 August 2018 at 15:22 Peter Constable via Unicode
<[email protected]> wrote:
Layout engines that support CJK vertical layout do not rely on the
'vert' feature to rotate glyphs for CJK ideographs, but rather
rotate the glyph 90° and switch to using vertical glyph metrics.
The 'vert' feature is used to substitute vertical alternate glyphs
as needed, such as for punctuation that isn't automatically rotated
(and would probably need a differently-positioned alternate in any
case).
Cf. UAX 50.
There have been some pretty confused statements. I believe the
observed problem is that PUA characters for Zhuang CJK ideographs get
rotated when displayed vertically rather than left-to-right.
Yes, as Richard says when CJK Zhuang text is displayed vertically whilst
the Zhuang characters in Unicode remain upright, but those with PUA
codepoints are rotated 90°. This is because the PUA characters are
treated like English text, which are correctly rotated 90°. The
orientation of the CJK characters in this case appears to depend on
which block they belong to. As Peter points out this does not seem to
match UAX 50.
Unicode is doing what it can in this matter:
(a) Zhuang PUA characters are being made individually obsolete.
Yes and No. Whilst a thousand Zhuang characters have been enocoded and
two thousand have been submitted via IRG, however the number of PUA
Zhuang characters is about the same or increasing. In 2006 when started
just under 6k PUA points were used, presently there are over 8k, over 6k
of which have not been submitted, and the earliest any future
submissions can be encoded is 2026. That being said the number of more
common Zhuang characters needing PUA support is coming down. So whilst
individual characters are being resolved, the need for PUA Zhuang
characters remains, and will so for decades to come.
(b) By default, PUA characters have the value of
Vertical_orientation=upright as do CJK ideographs.
Noted above.
Regards
John
For CJK ideographs, it is not clear to me when the vert feature (if
present) would be applied. Is it only for some codepoints (vo=tu), or
is it for all that the engine expects to be displayed 'upright' in
vertical text? The vrtr feature (if present) would be applied when
glyphs are to be rotated. Is it for all such glyphs, or only those
for which rotation is expected to be inadequate (vo=tr)? It seems
that feature vrt2 is to be applied to all glyphs; perhaps rotation is
the default behaviour when there is no look-up value for a glyph that
the engine expects to be rotated. The truly difficult case would be
when there is no attempt to apply a look-up - possibly vrtr would not
apply to /p{vo=r}.
I would expect that defining the lookup vrt2 or vrtr to map Zhuang
glyphs to themselves (or something prerotated) would cure the problem.
This would not work for sequences of Zhuang ideographs treated as RTL
text - but that is unlikely to happen.
Richard.
