[HarfBuzz] Multiple substitution and mark positioning

[Khaled Hosny]

This only applies to the marks that result of multiple substitution i.e.
in Amiri the middle lam of لله is substituted with
<lam><shadda><smallalef>, I don’t think Arabic Typesetting has something
like that.

On Wed, Jul 25, 2012 at 01:58:08PM -0400, Behdad Esfahbod wrote:
> This also happens with Arabic Typesetting I assume?
> 
> b
> 
> On 06/12/2012 06:31 AM, Khaled Hosny wrote:
> > I’m not sure if this is related, but I now get no mkmk positioning when
> > the marks are “inserted” using multiple substitution. For example, “للّٰه”
> > is positioned correctly, while “لله” is not though it is the same mark
> > glyphs except they are being added by multiple substation.
> > 
> > [uni0647.fina_Lellah=4+721|uni0670=1 at -267,-162|uni0651=1 at -277,-440|uni0644.medi_Lellah=1+473|uni0644.init_Lellah=0+319]
> > 
> > vs.:
> > 
> > [uni0647.fina_Lellah=2+721|uni0670=1 at -245,-440|uni0651=1 at -277,-440|uni0644.medi_Lellah=1+473|uni0644.init_Lellah=0+319]
> > 
> > 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
> >>> _______________________________________________
> >>> HarfBuzz mailing list
> >>> HarfBuzz at lists.freedesktop.org
> >>> http://lists.freedesktop.org/mailman/listinfo/harfbuzz
> >