[HarfBuzz] Display issue with DejaVu Sans Mono font

[Behdad Esfahbod]

If the font has a GPOS table, we won't do any fallback positioning.  As a
result, if font has missing data (anchors in this case), you get exposed to
that.

On Sun, Aug 18, 2019 at 4:06 PM Khaled Hosny <dr.khaled.hosny at gmail.com>
wrote:

>
>
> > On Aug 18, 2019, at 4:40 AM, Eli Zaretskii <eliz at gnu.org> wrote:
> >
> >> From: Khaled Hosny <dr.khaled.hosny at gmail.com>
> >> Date: Sun, 18 Aug 2019 00:48:14 +0200
> >> Cc: Harfbuzz <harfbuzz at lists.freedesktop.org>
> >>
> >>> https://lists.gnu.org/archive/html/bug-gnu-emacs/2019-08/msg01082.html
> >>>
> >>> Is there something wrong with this font when displaying this sequence,
> >>> or is there some kind of bug in Emacs and/or HarfBuzz?
> >>
> >> The second accent is placed next to the glyph, but hb-view is
> incorrectly clipping the image, as you can see from hb-shape output:
> >>
> >> $ hb-shape DejaVuSansMono.ttf -u '061,301,302'
> >> [aacute=0+1233|uni0302=0+0]
> >>
> >> Adding some margins gives:
> >>
> >> $ hb-view DejaVuSansMono.ttf -u '061,301,302’ --margin=0,150,0,0
> >>
> >>
> >>
> >> HarfBuzz will compose U+0061 + U+0301 to U+00E1 (since it prefers
> composed form when supported by the font), and that glyph does not have
> anchors to position any marks above it, so the circumflex ends up with its
> default position next to the glyph.
> >
> > So this is indeed some problem with that particular font?
>
> It is partly a font issue (missing anchors and combining marks default
> position to the left of base glyph), and partly HarfBuzz design decision of
> preferring composed forms. See
> https://github.com/harfbuzz/harfbuzz/issues/653.
>
> Regards,
> Khaled
> _______________________________________________
> HarfBuzz mailing list
> HarfBuzz at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/harfbuzz



-- 
behdad
http://behdad.org/
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