[HarfBuzz] the feature tag support in harfbuzz

[Behdad Esfahbod]

On 05/28/2012 07:27 AM, Akira TAGOH wrote:
> Hi Behdad and the list,

Hi Akira,

> I'm not looking at the code carefully yet, so I don't know if it's
> done or capable so far.
> 
> When I have ever proposed to support the Japanese related feature tags
> (jp78, jp83, jp90, jp04) in Pango
> (https://bugzilla.gnome.org/show_bug.cgi?id=624457), you suggested in
> the off list to do it in Harfbuzz and fontconfig. is it still a way to
> go right? how is it easy to implement in Harfbuzz now?

Yes.  There is no need to change anything in HarfBuzz right now.  The
remaining pieces are:

  - Figure out whether we want to add the feature markup in fontconfig branded
as fontconfig itself, or harfbuzz, or pango.  I'd say do plain fontconfig.
After all, Uniscribe and DirectWrite allow enabling arbitrary features too
these days.

  - Add fontconfig elements for turning features on / off.  Not sure about the
best format.  Maybe just support turning on?

  - In the harfbuzz-ng-external branch of Pango, in the basic-fc.c module, get
the features from the FcPattern and pass them to HarfBuzz.

That's all you need.  Later on we should also add API and markup to turn
features on/off from Pango itself.

> I'm still keen to see this feature to make things better and willing
> to go back the work on this.

Well, since most of the work now is on the fontconfig side, I believe you're
in the right position to do that!

behdad