[HarfBuzz] Cluster question (Was Cluster soap box time)

[Khaled Hosny]

On Thu, Dec 13, 2018 at 08:05:19PM -0800, Ansel Sermersheim wrote:
> On 11/29/18 7:29 AM, Behdad Esfahbod wrote:
> 
> > On Tue, Nov 27, 2018 at 8:34 PM Ansel Sermersheim <ansel at copperspice.com
> > <mailto:ansel at copperspice.com>> wrote:
> > 
> >     On 11/19/2018 07:16 PM, Behdad Esfahbod wrote:
> > >     Hi Ansel,
> > > 
> > >     On Mon, Nov 19, 2018 at 7:44 PM Ansel Sermersheim
> > >     <ansel at copperspice.com <mailto:ansel at copperspice.com>> wrote:
> > > 
> > >         ...We have tried cluster
> > >         levels 0 and 1, and neither one worked as we expected. In
> > >         every case,
> > >         combining accents are marked as being in a separate cluster
> > >         to the base
> > >         codepoint. For example, U+0061 Latin Small Letter A followed
> > >         by U+0308
> > >         Combining Diaeresis are being placed in adjacent clusters
> > >         rather than
> > >         the same cluster.
> > > 
> > > 
> > >     That doesn't sound right.  Are you setting any custom
> > >     unicode-funcs on the buffer?  Only thing I can think of that can
> > >     do this is faulty / missing Unicode funcs.
> > 
> >     We had a feeling something was missing. No, we are not supplying
> >     any unicode funcs. Do you have a sample or documentation reference
> >     for what we need to supply?
> > 
> > 
> > Not supplying anything is good.  Was just ruling out that as a cause.
> > 
> >     I have looked at the online documentation without seeing a clear
> >     list of what is required. We are specifically looking to use
> >     harfbuzz to decipher special case grapheme breaks.
> > 
> > 
> > Can you check with hb-shape command-line tool, to make sure what you
> > expect is what HarfBuzz produces there?
> 
> Sorry it took a while to get back with you, we really do appreciate your
> help. We have been looking over the code and we believe we are having a
> problem with missing unicode callback functions. We are compiling HarfBuzz
> with the following options turned on:
> 
> >    -DHAVE_ATEXIT
> >    -DHB_EXTERN=
> >    -DHB_NO_UNICODE_FUNCS
> >    -DHB_NDEBUG
> 
> I am particularly suspicious of the HB_NO_UNICODE_FUNCS define. Am I correct
> in thinking that this is suppressing the built-in harfbuzz unicode
> functions, so we must supply our own?

Yes. The simplest solution would to remove the define and make sure
src/hb-ucdn.cc and src/hb-ucdn are built (or if your code already
depends on ICU or GLib, you can alternatively build the corresponding
Unicode functions implementation).

Regards,
Khaled