[HarfBuzz] Issue with cursive attachment

[Behdad Esfahbod]

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, 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.

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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