Fwd: UAX#50 conformance: Is it possible to update existing fonts without causing damage to existing non-CSS applications?

---------- Forwarded message ---------
From: fantasai <fantasai@inkedblade.net>
Date: 2019年12月10日(火) 0:37
Subject: Re: UAX#50 conformance: Is it possible to update existing fonts
without causing damage to existing non-CSS applications?
To: Taro Yamamoto <tyamamot@adobe.com>, MURATA Makoto <
eb2m-mrt@asahi-net.or.jp>, Nat McCully <nmccully@adobe.com>
Cc: Florian Rivoal <florian@rivoal.net>


On 12/9/19 3:14 AM, Taro Yamamoto wrote:
>
> One example that was discussed at the last meeting with Murata--san:
U+2192 RIGHTWARDS ARROW, whose vertical posture is defined to be 'R' by
UAX50, but has been traditionally been included in the 'vert' table of
fonts based on the Adobe-Japan1-x Character Collection (glyph set) since
the late 1980s. According to Nat, InDesign assumes its vertical posture to
be 'Tr', so InDesign lets the 'vert' do the "pseudo-rotation" for the
corresponding glyph without any scruple.  There are very many similar
cases, where glyphs corresponding to the characters whose vertical postures
are defined to be 'R' by UAX50 are assumed to have the 'Tr' vertical
posture, and as a result, our fonts have them in the 'vert' features to do
the "pseudo-rotation". At this point, my guess may be wrong, but I have the
idea that without the assumption, if these characters had not been assumed
to have the 'R' vertical posture, as expected by UAX50 today, it would have
not been possible for anyone to guarantee that the glyphs corresponding to
these characters could have been rotated correctly at the very center of
the Japanese EM square type body. There is the distinction here between
Japanese glyphs and Western glyphs to be detected beforehand.

Ah, this is the tricky case. A 'vert' feature which implements Tr-style
rotated alternate instead of upright-style alternate for some glyph would
be
incompatible with the intention of UAX50/CSSWM for that glyph.

I wonder if there are many examples other than arrows?

> However, as far as the 'vert' features are concerned, which are in font,
for any font developers, it is self-explanatory whether a font is for
Japanese or Western languages/scripts. So, by having the 'vert' features do
the "pseudo-rotation", applications seem to have been free from the
responsibility of rotating Japanese glyphs at the center of their EM square
type bodies. Whatever type of glyphs, Japanese full-width characters or
Western proportional glyphs, as far as applications position them correctly
by rotating and shifting them, understanding how they should be positioned
in Japanese vertical lines, it is not necessary to have those 'R' glyphs in
the 'vert' features, but it is possible to have applications really rotate
and shift them. But I guess it was impossible to assume all applications
really could do it in those days. But is it possible to guarantee that they
do it rightly at the end of 2019?

We think there are definitely glyphs for which a rotated presentation needs
an
alternate glyph rather than a simple rotation by the application. But this
is
why the 'vrtr' feature was added to OpenType. For such characters, it is
intended for the application to rotate them, and the font to provide a
'vrtr'
alternate for vertical presentation of a rotated glyph.

The CSS Writing Modes system uses the combination of this 'vrtr' feature,
the
application’s ability to set any character upright or not upright
(defaulting
to UAX50), and the 'vert' feature as intended for truly upright typesetting
of
each character (excepting those such as brackets for which an upright
presentation would be nonsensical, which are marked as Tr in UAX50). This
should give authors, applications, and fonts together the ability to
typeset
text perfectly in each case,

The concern for compatibility of fonts with such a system then seems to be
whether fonts have 'vert' alternates that rotate characters which, in a
fully
upright typesetting style, could be upright. For example, the case of
arrows
you discuss above. In such cases, there is no way to set that glyph upright
except maybe to disable the 'vert' feature.

~fantasai



-- 
Regards,
Makoto