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Re: [css-fonts] proposal needed for synthesizing oblique fonts in vertical text

From: MURAKAMI Shinyu <murakami@antenna.co.jp>
Date: Sat, 18 May 2013 13:45:34 +0900
To: www-style@w3.org
Message-Id: <20130518134533.59C1.C598BCD7@antenna.co.jp>
John Daggett <jdaggett@mozilla.com> wrote on 2013/05/16 12:18:54
> I'm proposing that synthetic italics have behavior that's consistent with
> real italics and the synthesized glyph is in no way dependent on writing-mode
> or text-orientation.  In the illustration I posted, that would be option #1:
> 
> http://lists.w3.org/Archives/Public/www-archive/2013May/att-0027/synthetic-italics-tategaki.png

I have the same opinion with John. Synthetic italics should be consistent 
with real italics.

I understand some of Koji's concern about this behavior but I believe 
this is the most better choice: "#2 Top edge to right" (in upright orientation):
http://koji.ec/archives/32

| #2 Top edge to right is one way to implement naturally. If an 
| implementation renders a glyph in upright in vertical flow, 
| existing code will slant the top edge to right, so this behavior 
| requires the least work for such implementations. But this is 
| the only case where slant is applied orthgonally to the baseline, 
| which poses some issues such as:
| 
| 1. Characters will overlap with underlines if drawn on right.
| 2. Ruby and emphasis marks will not align if slanted together, or 
|   overlap with base characters if they don’t. How to handle such cases 
|   need to be determined.
|   If we want to slant ruby in the same way as the base character, 
|   UA needs an additional code to slant baseline.

I think these issues are not so important. "Synthetic italics" are a fallback
behavior and we cannot expect perfect results.
Professionals should not specify 'italic' to Japanese vertical text in general.

If you think the ruby and synthetic italics issue seriously, you should 
also think about the bopomofo ruby with synthetic italics, this causes
same problem even in horizontal writing mode (bopomofo ruby is placed on
the right side).

| 3. Oftentimes UA renders a glyph in upright, but the glyph looks rotated 
|   sideways because font has a rotated glyph. This results in inconsistent 
|   look, since both sideways-rendered glyphs and upright-rendered glyphs 
|   look similarly rotated to users, but they slant differently.
| 4. Unicode unifications unified many symbols and punctuation characters 
|   between Latin and East Asian scripts. This will result in some symbols 
|   and punctuation characters used commonly in Latin script drawn upright, 
|   or vice versa.
|   This, combined with #3 above, can break applying Italic to regular 
|   Latin text. Which characters will break depends on fonts’s tables, 
|   but EAW=A characters are the possible candidates.

UTR50 defines the default character orientations and CSS3 Writing Modes
says “When ‘text-orientation’ is ‘mixed’, the UA must render a character 
upright if its orientation property is U, T, or Tu; or typeset it sideways
(90° clockwise from horizontal) if its orientation property is R.”

Sideways-rendered glyphs or upright-rendered glyphs are determined by the
UTR50 property values of the code points, and it seems natural that while
the synthetic italics of upright glyphs are slanted to the right, the 
synthetic italics of sideways (rotated) glyphs are sloped down to the right.

We can get consistent results with this way. Dash characters are sideways 
(vo=R in UTR50) and two em-dashs keep straight and continuous.

| 5. There are some code points that are supposed to connect; 
|   U+2014 EM DASH, U+2015 HORIZONTAL BAR, and U+2026 HORIZONTAL ELLIPSIS 
|   are the examples. These code points look broken if slanted this way, 
|   both in Latin and Japanese. Other examples are U+3033-3035 
|   VERTICAL KANA REPEAT MARK UPPER HALF/LOWER HALF. Implementations need 
|   to create a table of code points that should not be slanted.

About U+2014 EM DASH, U+2015 HORIZONTAL BAR, and U+2026 HORIZONTAL ELLIPSIS
there are no a problem as mentioned above.

Synthetic italics of U+3033-3035 VERTICAL KANA REPEAT MARK UPPER HALF/LOWER HALF 
will be problematic, but appearances of these characters are very rare in 
modern Japanese text. Authors should avoid specifying italic in context
where these characters are used.

Regards,

Shinyu Murakami
Antenna House
Received on Saturday, 18 May 2013 04:45:59 UTC

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