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9日(月) 15:36
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 12/2/19 3:04 AM, Taro Yamamoto wrote:
>
> As I have repeated, the switching of glyph postures in Japanese
typesetting are ruled mainly by application software. The area that the
'vert' feature really can control is relatively small.

The 'vert' feature should not, in general, be controlling the rotation of
glyphs other than Tr glyphs. It should provide alternates for upright
typesetting, for when the application indicates to the font that this run
of
text will be upright.

If a font is compatible with application software that can take any glyph
and
override its orientation to be upright or sideways, then it is definitely
compatible with CSS Writing Modes and UAX50.

> So, what you wrote in the "Document" is only half the domain of the
possible problems of vertical glyph posture inconsistency with UTR #50.
> For example, If you type a COPYRIGHT SIGN U+00A9 character in a vertical
line on some page layout application software, the result posture will be
often  different from that defined by UTR #50. These applications treat it
as an R-vertical-posture character, and rotate it 90 degrees, but the
character must have the vertical posture of U according to UTR #50. This is
only ONE example of the inconsistency problems that you are concerned
about, but the 'vert' feature in font is NOT responsible for this problem
that occurs to the U+00A9 character at all, because the character is NOT
included in the 'vert' feature. This problem of U+00A9 is not a 'vert'
problem at all.

This is an example of UAX50 having a different default orientation than
such a
page layout application software. This is why such software, as Nat
explains,
cannot "upgrade" itself to match UAX50, but has to offer it as an opt-in
option.

It is not an example of an incompatibility of the font with UAX50.

UAX50 is only a table of defaults, similar to the one in InDesign that
decides
whether the default orientation of a glyph should be upright or sideways,
but
with potentially some different values.

> (On the other hand, this also means that as long as the 'vert' produces a
variant glyph shape whose vertical posture is still Upright, there will be
no problem, even if the vertical glyph design has some difference from the
original Upright shape with the effect of the 'vert' feature, usually the
vertical glyph shape is what is expected by the type designer. This kind of
glyph substitution by the 'vert' feature must be allowed.)

Yes. This is the intention of the 'vert' feature.

~fantasai



-- 
Regards,
Makoto