571372 - Consider supporting IVS-based font fallback

Status: RESOLVED DUPLICATE of bug 392588

(Core :: Graphics, defect)

Description

[Masatoshi Kimura [:emk]]

HanaMin (花園明朝) supports all Ideographic Variation Sequences which are defined in Adobe-Japan1 collection. But I do not want to set this font as a default Japanese font because its glyph quality is not so good. HanaMin is intented to be a "Last Resort" font for Japanese Kanji.
Currently I have to select HanaMin explicitly every time IVS appears in the text. Obviously I'ts impossible when I'm visiting random Web pages. Moreover, I can't select fonts in plain text context (for example <textarea> and <input type="text">).
It's the purpose of IVS to express glyph restrictions in plain text.
http://www.unicode.org/reports/tr37/tr37-5.html#w1aab7b1

Comment 1

[John Daggett (:jtd)]

Sorry, I'm not clear what you're requesting here.  Are you saying that when variation sequences exist they should fallback until a font is found, including system fallback fonts?

So something like:

1. For each font in the fontlist (i.e. font-family value), look for <base> + <variation-selector> mappings.  Choose the first font that does.

2. If no fonts support <base> + <variation-selector>, fallback to system fonts, looking for the first font that supports the variation.

3. If (1) and (2) fail to find a match, run the normal font matching procedure with only the <base> character and ignore the <variation-selector>.

Looking over the code, current behavior is effectively:

1. Find the first font that matches <base>

2. If a variation exists for that font, use that, otherwise use the default glyph.

So in effect, the current behavior will only have effect when the first font containing the <base> character also has a given variation, otherwise the variation selectors will effectively be ignored.

Comment 2

[Masatoshi Kimura [:emk]]

(In reply to comment #1)
> Sorry, I'm not clear what you're requesting here.  Are you saying that when
> variation sequences exist they should fallback until a font is found,
> including system fallback fonts?
Right. Although I can compromise about system fallbacks, at least I want to handle a case such as |font-family: 'MS Mincho', KozMin-Pr6N, IPAmjMincho;|.

Comment 3

[Masatoshi Kimura [:emk]]

Bug 392588 is older and more generic.