[HarfBuzz] Issue with cursive attachment

[Khaled Hosny]

On Tue, Aug 25, 2015 at 05:06:12PM +0100, Behdad Esfahbod wrote:
> Basically what's happening is this:
> 
>   - Lookup 0 joins gid9 to gid6 saying that gid9 should stay on the baseline,
> 
> then:
> 
>   - Lookup 1 joins gid6 to git8 saying that gid8 should stay on the baseline.
> 
> Essentially gid6 is attached to two different sides...  I call this a faulty
> font,

It is a hack (but necessary one) that I didn’t even expect to work, but
it worked in Uniscribe.

> but I'll work something out to match Uniscribe to the extent possible.
> I suppose the later connection shall win, ie. gid8 stays on baseline and
> everything else adjusted to follow.

Yes, that is what Uniscribe is doing and my “expected” result.

Regards,
Khaled

> b
> 
> On 15-08-23 04:58 PM, Khaled Hosny wrote:
> > I’ve a problem with mixing cursive attachment lookups with RTL flag set
> > on some of them and not the others.
> > 
> > I’m attaching two minimal fonts showing this issue, the only different
> > between the good and bad fonts is that the bad font has a cursive
> > attachment lookup with RTL flag not set while all the others have it
> > set, and HarfBuzz seems to not to apply that lookup on the same word
> > where the other lookups are applied.
> > 
> > Testing with the word كمثل, the anchor between the 2nd and 3rd glyphs
> > (from right) is not applied in the bad font but applied in the good one.
> > Both DirectWrite/Uniscribe and Core Text apply it fine in both fonts
> > (though Core Text has other serious problems).
> > 
> > If I unset the RTL bit on all the cursive attachment lookups, it renders
> > correctly in HarfBuzz.
> > 
> > (If you are wondering why I’m doing this, it is because for some of my
> > cursive attachments I want rightmost glyph to stay in its natural
> > position and the other glyphs attached to it instead of having the
> > leftmost glyph stay in its natural position.)
> > 
> > Regards,
> > Khaled
> > 
> > 
> > 
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> >