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[css-fonts] selecting color or monochrome glyphs for emoji fonts

From: John Daggett <jdaggett@mozilla.com>
Date: Thu, 21 Aug 2014 00:37:52 -0700 (PDT)
To: www-style list <www-style@w3.org>
Cc: public-webfonts-wg <public-webfonts-wg@w3.org>
Message-ID: <1028799912.16539036.1408606672362.JavaMail.zimbra@mozilla.com>

As emoji fonts gain popularity across platforms, authors are
starting to run into problems where they end up getting a color
emoji glyph for a symbol they desire to be monochrome (for an
example bug report, see [1]). I'm thinking it might make sense to
have a CSS property to allow authors to explicitly control this:

  font-variant-color: auto | color | monochrome
  initial value: auto

The 'auto' value means the user agent determines which to use. In
some contexts, it might make sense to prefer monochrome glyphs (e.g.
a reader app) while in other contexts color glyphs might always be
preferred (e.g. a messaging app). Or a user agent might decide this
based on codepoint, using color glyphs for the emoji range
(U+1F300–1F5FF) while preferring monochrome glyphs for standard
Unicode symbol ranges.

The 'color' value means use color glyphs if available, the
monochrome glyph otherwise. The 'monochrome' value means avoid using
the color glyph and use the monochrome glyph.

Like other font-variant property values, this would only affect
glyph selection. If alternate glyphs are not available, using this
property would not affect how text is rendered. User agents must not
try and simulate fallback glyphs for fonts lacking color glyphs.

For authors, this property would assure that they didn't need to
worry about which font is used on which platform. By using
'font-variant-color: monochrome' they would guarantee that they
wouldn't see color glyphs.

I should note here that all the color font formats in use currently
(Apple/Google/Microsoft/SVG) all add additional tables to a TrueType
font to contain the color glyph data. So there are typically
monochrome glyphs for all characters but not necessarily color
glyphs.

Thoughts?

Regards,

John Daggett
Mozilla Japan

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1054780
Received on Thursday, 21 August 2014 07:38:20 UTC

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