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Re: [css-ruby] Tone mark of bopomofo in ruby

From: Koji Ishii <kojiishi@gmail.com>
Date: Sat, 24 Jan 2015 17:03:22 +0900
Message-ID: <CAN9ydbWLEHcf5B5NFTXvXF5kHETZj+ztWETi1z+xZ8EO+gYHzA@mail.gmail.com>
To: Bobby Tung <bobbytung@wanderer.tw>
Cc: Xidorn Quan <quanxunzhen@gmail.com>, www-style list <www-style@w3.org>, CJK discussion <public-i18n-cjk@w3.org>
I had an impression that someone has solved somehow and Bobby knows
that, because WebKit has implemented inter-character already. It's a
bit unfortunate to know that this wasn't solved yet.

I agree with Xidorn that this should be solved outside of the ruby spec.

So, both of you know the spec/algorithm to layout Bopomofo tonemarks?
I suspect still-in-work CLREQ might cover that, but if there was a
polyfill on github, that'd be a great first step. It helps authors,
and it may help possible contributors with font knowledge to
understand the necessary spec/algorithm.

/koji

On Fri, Jan 16, 2015 at 10:11 AM, Bobby Tung <bobbytung@wanderer.tw> wrote:
> Hi Xidorn,
>
> I remember this issue is discussed in TPAC 2014 ruby session. Layout Engine
> and fonts' GPOS are ok for the tone marks.
>
> But fonts vary and may take longer for penetration. I'd like to hear more
> comments from implement side for the issue.
>
> WANDERER Bobby Tung
> Sent from my iPhone.
>
> Xidorn Quan <quanxunzhen@gmail.com> 於 2015年1月16日 上午8:38 寫道:
>
> Hi,
>
> The current CSS Ruby spec requires UAs to position the tone marks in ruby
> annotation properly in the note below "ruby-position: inter-character;" [1]
> and I was trying to implement this during the last few days. But it then
> makes me wonder whether it is worth to implement this in layout engine.
>
> The first reason made me think about this was the fact told by Bobby that
> the tone marks are always positioned in a separate column for vertical
> bopomofo in all contexts, not only when they are inside ruby annotation.
> Which means, the tone mark positioning is not limited to inter-character
> ruby; it also covers ruby and non-ruby text in vertical text. It is
> definitely what fonts should handle.
>
> The other potential problem for this is that, it will never be interoperable
> until all UAs implement this in the same way. There are a lot of details
> need to be considered, for example, what tone marks should be repositioned?
> Only trailing ones, or every one? What exactly position the tone mark should
> be placed when font or font size vary? It would be hard for author to detect
> whether a UA support the tone mark positioning, and how it is implemented.
>
> In conclusion, I don't think it is a good idea to implement tone mark
> positioning in layout engine. It would affect interoperability and
> complicate the impls. The positioning should be handled by fonts.
>
> However, we know that no fonts seem to support this currently. They even
> display a rotated tone mark in vertical text. For this, I suggest we use
> polyfiller to do the positioning. It would be easier to implement this in
> JavaScript and DOM, a polyfiller also provides more flexiblilty for authors
> to control over the behavior. Once the fonts start supporting this, authors
> can simply remove the polyfiller.
>
> The attachment is a simple polyfill demo for tone mark positioning. It seems
> to work almost fine with Trident and WebKit (with a little problem with
> Gecko, though, because of the incomplete ruby impl)
>
> - Xidorn
>
> [1]: http://dev.w3.org/csswg/css-ruby/#valdef-ruby-position-inter-character
>
> <tone-mark-positioning.html>
Received on Saturday, 24 January 2015 08:03:49 UTC

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