[webkit-dev] Adding CSS3 font feature propreties

[Kenichi Ishibashi]

Hi webkit-dev,

I'm thinking about adding CSS3 font feature properties[1] support to WebKit.
 It allows page authors to control over advanced typographic features.
 Firefox has an experimental implementation and an article[2] shows how
these properties work.  I really would like to add this feature so I'd like
to ask comments and suggestions in advance.

My current plan is starting with adding the font-feature-settings property
(6.12 Low-level font setting control) as -webkit-font-feature-settings,
following a similar approach that Firefox did.  For OpenType fonts, other
properties can be treated as specific cases of the font-feature-settings
property and I think adding this property is good starting point.

One shortcomings of this approach is that it requires OpenType support for
each port.  A port which uses AAT might not be able to support this
property, or we need to add an extra text rendering subsystem which can
handle OpenType features to the port.

If I get started with this plan, I will start implementing css parsing part,
then implement font rendering part on a specific port (Chromium Linux port
is in mind for now) on trial.

I'd also like to put some notes of supporting CSS3 font feature properties
with AAT and CoreText here:
- AAT features are listed at [3].
- While the spec lists the equivalent OpenType feature tag for each
property, it is unclear that what AAT feature setting corresponds with each
property.  An email written by the spec editor[4] lists them partially but
not complehensive.
- [5] describes OpenType support of CoreText (I'm not sure this is correct,
though).

Comments and suggestions are highly appreciated.

[1] http://dev.w3.org/csswg/css3-fonts/#font-rend-props
[2] http://hacks.mozilla.org/2010/11/firefox-4-font-feature-support/
[3] http://developer.apple.com/fonts/registry/
[4] http://lists.w3.org/Archives/Public/www-style/2009Jun/0506.html
[5] http://en.wikipedia.org/wiki/OpenType_feature_tag_list

Regards,
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