[HarfBuzz] Retrieving optical size info?

[Khaled Hosny]

On Tue, Nov 27, 2012 at 04:00:49PM +0000, Jonathan Kew wrote:
> On 27/11/12 15:37, Khaled Hosny wrote:> On Mon, Nov 26, 2012 at
> 02:03:15PM +0200, Behdad Esfahbod wrote:
> >> On 12-11-24 10:58 PM, Khaled Hosny wrote:
> >>> On Sat, Nov 24, 2012 at 01:05:26AM -0500, Behdad Esfahbod wrote:
> >>>> On 12-11-23 07:42 PM, Khaled Hosny wrote:
> >>>>
> >>>>> (Background: I’m almost done with porting XeTeX from ICU
> LayoutEngine to
> >>>>> HarfBuzz, one of the few things remaining is getting optical
> size. The
> >>>>> current code uses some internal LE API and I want to move away
> from this
> >>>>> as possible).
> >>>>
> >>>> Sure, I'll implement it in HarfBuzz for you!
> >>>
> >>> Great!
> >>
> >> Done.  Untested though.  Let me know if it works!
> >
> > Thanks Behdad. It seems that looking for ‘size’ feature under default
> > script does not work, with the attached patch which makes it check all
> > GPOS features, things work fine.
> >
> > Now what remains is handling fonts with broken ‘size’ feature that AFDKO
> > used to make prior 2006, but I’m yet to find documentation for it (Adobe
> > is said to have sent some explanation for a heuristic to handle broken
> > ‘size’ features to OpenType mailing list somewhere in 2006, but I don’t
> > have access to list archives).
> >
> 
> I don't seem to have that mail on hand either, but IIRC the existing
> xetex code includes heuristics to handle this, so you could probably
> just use that as a guide.

I was hoping for some plain language :) anyway the relevant part of the
old code is:
https://github.com/mojca/xetex/blob/15b7827a5d8344c685fe27128cd4a03a729e1ee2/texk/web2c/xetexdir/XeTeXFontMgr.cpp#L492

I tried to replicate this in HarfBuzz but I couldn’t find a simple way
to get the FeatureList offset and pass it to get_feature_params() (and
all non-simple ways I came up with failed of course :).

Regards,
 Khaled