[HarfBuzz] How to get a glyph code for a character?

[Khaled Hosny]

On Sat, May 25, 2019 at 06:08:42PM +0300, Eli Zaretskii wrote:
> > Date: Sat, 25 May 2019 15:50:38 +0100
> > From: Richard Wordingham <richard.wordingham at ntlworld.com>
> > 
> > I presume you're after the glyph indicated by the raw cmap, e.g.
> > without localisation.
> 
> Not sure what kind of localisation are you alluding to here.  I must
> confess that I'm relatively ignorant about fonts, glyphs, and shaping,
> so I'm probably missing a lot here.  For example, I have no idea what
> is a "raw cmap".

For any given script and language, the font might provide a different
localized glyph than the default one. Only hb_shape[_full]() will apply
such localization.

> > Using hb_shape could very well result in the addition of a dotted
> > circle for a combining mark - is that what you want?
> 
> AFAIK, this method is only called in Emacs for a combining mark when
> we indeed want it displayed as a separate character, with the dotted
> circle.  It is normally called for base (non-combining) characters.

Then hb_shape() is the right tool here. HarfBuzz will also automatically
insert dotted circle for combining marks that are at the start of the
text string if HB_BUFFER_FLAG_BOT is set on the buffer. You can safely
set HB_BUFFER_FLAG_BOT and HB_BUFFER_FLAG_EOT on any buffer as long as
the text passed to hb_buffer_add* functions is the full paragraph text
not just a chunk of it (that is another reason why one should pass the
full paragraph and the item offset and length to these function instead
of just the substring).

Regards,
Khaled