[HarfBuzz] how to detect missing glyphs e.g. for font substitition

[Khaled Hosny]

On Wed, May 13, 2015 at 10:14:48PM +0400, Konstantin Ritt wrote:
> 2015-05-12 14:12 GMT+04:00 Konstantin Ritt <ritt.ks at gmail.com>:
> 
> > 2015-05-12 5:41 GMT+04:00 Behdad Esfahbod <behdad.esfahbod at gmail.com>:
> >
> >> On 15-05-11 08:06 AM, Konstantin Ritt wrote:
> >> > Uniscribe has an API to override the .notdef glyph's value
> >>
> >> I didn't know this.  Which API is that?
> >>
> >
> > Turns out I was lying a bit ;)
> >
> > There is an API to *retrieve* the .notdef glyph's value:
> >
> > https://msdn.microsoft.com/en-us/library/windows/desktop/dd368802(v=vs.85).aspx
> > (see wgDefault & wgInvalid)
> >
> 
> wgDefault is probably the 'OS/2' table's "usDefaultChar" field, which is
> usually set to 0x0000 or to 0x0020 (dunno if we use it somewhere).

Use of usDefaultChar is “strongly discouraged” per the spec anyway.

Regards,
Khaled