[HarfBuzz] [p-c] Perso-Arabic symbols for "year"

[Khaled Hosny]

On Thu, May 31, 2012 at 01:00:31AM -0400, Behdad Esfahbod wrote:
> On 2012-05-28, at 10:29 PM, Khaled Hosny <khaledhosny at eglug.org> wrote:
> 
> > On Mon, May 28, 2012 at 07:50:55PM -0400, Behdad Esfahbod wrote:
> >> [CC'ing Khaled and HarfBuzz list]
> >>
> >>>
> >>>
> >>>
> >>
> >> This block:
> >>
> >> feature calt {
> >>  sub                                              @YearSign @Digits' lookup digit2medium;
> >>  sub @Digits.medium                               @YearSign @Digits' lookup digit2medium;
> >>  sub @Digits.medium @Digits.medium                @YearSign @Digits' lookup digit2medium;
> >>  sub @Digits.medium @Digits.medium @Digits.medium @YearSign @Digits' lookup digit2medium;
> >> } calt;
> >>
> >> Looks completely wrong to me in that it matches the backtrack sequence in the
> >> wrong order.  Ie, from what I understand, and I can be totally wrong, it
> >> should have lines like this:
> >>
> >>  sub @YearSign @Digits.medium @Digits.medium    @Digits' lookup digit2medium;
> >>
> >> instead of this:
> >>
> >>  sub @Digits.medium @Digits.medium    @YearSign @Digits' lookup digit2medium;
> >
> > AFAIK the backtrack coverage has to be in the reverse order, if I do as
> > you suggest, only first digit will be matched. This have been tested
> > with FireFox¹ (hb-ng), Pango (hb-old), LibreOffice (ICU) and MS Word
> > (Uniscribe), so I think it is correct² :)
> 
> Reporting back from the Adobe communication thread:
> 
> So, apparently Adobe meant the backtrack sequence to be in logical
> order, not reversed. Combining this with Khaled's observation of the
> font working can only suggest that Fontforge is producing backtrack
> table in reverse. Fixing that will break all fo ts relying on that
> behavior of Fontforge. Khaled is to investigate more to figure out how
> to proceed.

This have been fixed in FontForge’s master branch, it will break feature
files expecting the older behaviour, but there is not much we can do
here, and it is hardly the only incompatible fix to FontForge’s feature
file code since the last release.

Regards,
 Khaled