- From: Eric Muller <emuller@adobe.com>
- Date: Wed, 22 Feb 2012 11:33:09 -0800
- To: www-style <www-style@w3.org>
- Message-ID: <4F4542F5.9030405@adobe.com>
> 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.
Received on Wednesday, 22 February 2012 19:33:56 UTC