[HarfBuzz] Question about zero width glyphs in shaping output

[Ebrahim Byagowi]

Probably this bug https://github.com/googlei18n/noto-fonts/issues/212 is
related.

On Tue, Dec 8, 2015, 2:44 PM Khaled Hosny <khaledhosny at eglug.org> wrote:

> On Mon, Dec 07, 2015 at 09:13:23PM +0530, Deepak Jois wrote:
> > Maybe this is a bit related to Khaled’s question earlier about control
> > characters inside ligatures, but I wanted to start a new thread.
> >
> > When I shape text with Noto Nastaliq, I notice a bunch of zero-width
> > glyphs generated
> >
> > $> hb-unicode-encode U+06CC,U+06C1 |  hb-shape notonastaliq.ttf
> > [HehFin=1+472|TwoDotsBelowNS=0 at 310,-383+0|sp2=0+0|BehxIni.outS1=0 at 0
> ,-68+731]
> >
> > 1. What is the purpose of these zero-width glyphs?
>
> That is something internal to the font, they are not glyphs inserted by
> HarfBuzz.
>
> > 2. If I am rendering the shaped output to a PDF file (for e.g. when
> > using Harfbuzz with LuaTeX), do I need to care about these zero-width
> > glyphs at all? How will they affect rendering
>
> You should just output the glyph as returned by HarfBuzz,
> second-guessing it is likely to be wrong. If a character should be
> invisible HarfBuzz will replace it by the space glyph, so you need not
> worry about this, unless you really know what you are doing.
>
> Regards,
> Khaled
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