Western vertical texts

>     Steve: But since then he concluded that upright is not a character-level
>            property.
>     Steve: Sometimes cluster.
>     Steve: (He didn't send that proposal yet.)
>     Steve: A mode in text combine that does the grouping in vertical stacking case.
>     Steve: More TCY and" IJ" in Dutch kind of thing.
>     John: So none of us heard this before.

I emailed that observation to John, fantasai, and Koji on 1/26, title 
"UTR50 / Mongolian".


When looking at running text, we can observe that the bulk of the cases 
concern text that is set tight, i.e. the letters are one next to the 
other. Over time, various mechanisms have been used to make such texts 
more legible: ligatures, kerning, contextual shaping, etc.

In some situations, the text is not set tight: when letterspacing is 
introduced, when displaying on a path. With enough letterspacing, or 
with paths that are far enough from a straight line, the mechanisms 
intended for tight text no longer work, and in fact are undesirable. 
Vertical western text is in the same situation from the get-go; it's 
really text on discontinuous path.

Furthermore, vertical western text is used predominantly in signage 
contexts rather than in running text. More often than not, additional 
graphic considerations enter in the setting: an article or other small 
word is set horizontally;  apostrophes and periods may be placed 
together with other letters rather than separately; in general, whatever 
works for the sign in question, in the context in which the sign is used.

It seems to me that a line western vertical text is therefore better 
understood not as a line in which individual "characters" are rotated 
(in the style of East Asian vertical lines), but as a line in which 
fragments are treated independently and stacked in a line, where the 
fragments are generally "characters" but may be larger. In fact, the 
machinery for Japanese Tate-chu-yoko (TCY, horizontal in vertical) seems 
to be just the ticket.

This view is also supported by implementation considerations. Most 
western fonts that include ligatures, kerning, etc are not built to be 
used vertically. When processing a run that contain "f" and "i" stacked, 
most OT fonts will not react to the clue of that "f" is below "i" (i.e. 
that the 'vert' feature is applied to those), and will do exactly the 
same thing as if "f" was on the left of "i". The implication for layout 
engine is that they will need to shape each "character" or fragment 
separately; and this is already what happens with TCY.

Therefore, what I would recommend is to handle western vertical text via 
text-combine:all rather than via text-orientation:upright.



The same considerations apply a priori to Japanese vertical text, but 
there are important differences. First, we are speaking about massive 
amounts of text, rather than an occasional isolated line here or there. 
Second, the fonts using in that context are typically reacting to 'vert' 
and the font themselves ensure that an "f" with an "i" below it do not 
form a ligature, or do not kern. Finally, users in Japan are probably 
much more aware that some fonts do not function correctly in vertical 
settings, which allow implementation to not go to extreme lengths to 
avoid incorrect output, when the font is not suitable.


Eric.