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RE: [css3-fonts] Font fallback for grapheme cluster and IVS

From: Koji Ishii <kojiishi@gluesoft.co.jp>
Date: Sat, 28 May 2011 08:27:36 -0400
To: John Daggett <jdaggett@mozilla.com>
CC: "www-style@w3.org" <www-style@w3.org>
Message-ID: <A592E245B36A8949BDB0A302B375FB4E0AC29AEA05@MAILR001.mail.lan>
>> The former is if the UA should use code point for font fallback, or
>> grapheme cluster. My vote is to use grapheme cluster, but I'd like
>> to wait for John's investigations.
> I don't think there's anything to vote for here, the question is how
> best to do font selection for grapheme clusters that involve more than
> a single codepoint.  This was discussed on the list back in February
> and I think the description Eric Muller outlined makes
> the most sense.

I'm glad to hear that you agreed with Eric Muller's message[1], I agree with that too.

>> IVS has yet another issue; IVS defines its fallback mechanism, and
>> CSS3 Fonts defines its fallback mechanism too. The question is how
>> these two fallback mechanisms should be combined to work together.
> You're comparing apples and oranges here.  The IVS spec defines
> codepoint fallback, it does not define *font* fallback.  The nature of
> the IVS database adds a number of complications to this issue here, as
> I noted back in February on the list [2].

I'm sorry that my wording was incomplete and misleading. You're right that the two are different things, but what I wanted to say here was that there's no clear agreement where the IVS codepoint fallback should fit into the logic Eric described[1].

> As I pointed out back in February, over 90% of the variation selectors
> among the Adobe-Japan1 selectors are the default glyph, so for those
> selectors the "ideal" fallback will be Option 1, not Option 2, for
> fonts lacking an IVS cmap.

I agree with you here. But you could also find that over 55% of the variation selectors among the Hanyo-Denshi selectors are not the default glyph today, and such Hanyo-Denshi selectors is going to increase to over 70% by the end of FY2011. I hope you understand that the situation is gradually changing and improving after the initial Adobe-Japan1 release.

I talked about this with Yasuoka-san, the author of the blog and the article you pointed[3]. He agreed with you that option 1 is ideal if the spec must be written based on what we have with current Adobe-Japan1 selectors, but he also said option 2 is ideal if we look at later releases (Hanyo-Denshi) and future.

Since today's situation splits, i.e., option 1 for Adobe-Japan1 and option 2 for Hanyo-Denshi, if you believe that it's too early to spec it out, I have to agree to postpone it. But logically speaking, there's no way to add more default glyphs, so all glyphs being added to Adobe-Japan1/Hanyo-Denshi are new glyphs. It's going to favor option 2 more as time goes. I hope you understand this.

It looks like you agree that option 3 is not a good way to handle IVS, that's a great news to me.

> p.s. Hopefully there won't be more IVS selector registrations that overlap existing
> ones but that may be wishful thinking.

I can't agree more. There's a proposal to allow sharing IVSes across IVD[4], which I hope improves the situation further.


[1] http://lists.w3.org/Archives/Public/www-style/2011Feb/0818.html

[2] http://lists.w3.org/Archives/Public/www-style/2011Feb/0799.html

[3] http://itpro.nikkeibp.co.jp/article/COLUMN/20110124/356398/

[4] http://www.unicode.org/review/pri184/

Received on Saturday, 28 May 2011 12:27:34 UTC

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