[HarfBuzz] Multiple substitution and mark positioning

[Khaled Hosny]

Thanks Behdad!

Works fine so far :)

Regards,
 Khaled

On Fri, Jun 08, 2012 at 10:14:19PM -0400, Behdad Esfahbod wrote:
> Hi Khaled and others,
> 
> I fixed this, among other things, including a major mlig and mkmk regression.
>  Please test.
> 
> behdad
> 
> On 05/12/2012 08:54 AM, Khaled Hosny wrote:
> > Hi all,
> > 
> > There seems to be a difference between HarfBuzz and Uniscribe on how to
> > handle mark positioning when there is multiple glyph substitution,
> > namely HB seems to apply the mark to the last component while USP
> > applies it to the first component.
> > 
> > In other words, if there is <base> → <base₁><base₂> substitution, the
> > sequence <base><mark> will be rendered as if it was <base₁><base₂><mark>
> > with HB, but as <base₁><mark><base₂> with USP.
> > 
> > Using hb-shape with “uniscribe” shaper, and the word “سَتا” and Arabic
> > Typesetting font, I get
> > 
> >   [uniFE8E=3+343|uniFE98=2+376|uni064E=0 at 501,-260|uni0640.curvehalf=0@,34+152|uniFEB3=0@,34+840]
> >                                          ^^^^^^^^
> > but with “ot” shaper, I get:
> > 
> >   [uniFE8E=3+343|uniFE98=2+376|uni064E=0 at -11,-310|uni0640.curvehalf=0@,34+152|uniFEB3=0@,34+840]
> >                                          ^^^^^^^^
> > though the glyph string is the same, the position of the mark is clearly
> > different.
> > 
> > (background: I need this to contextually insert tatweel to avoid mark
> > collision in “crowded” places, but with the difference between both
> > engines this can’t be reliably done without breaking mark positioning in
> > one of them).
> > 
> > Regards,
> >  Khaled
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