[HarfBuzz] Shaping different scripts in the same text run

[Khaled Hosny]

Please note that characters with common or inherited script property
need special treatment, the corresponding Pango code is in
pango/pango-script.c

Regards,
Khaled

On Sun, Apr 07, 2013 at 02:07:15PM +0200, Lóránt Pintér wrote:
> Thanks. I could manage to do this by using ucdn_get_script() for now. BiDi is going to be the next big challenge.  
> 
> --  
> Lóránt Pintér
> Developer at Prezi (http://prezi.com)
> 
> 
> 
> On Sunday, April 7, 2013 at 1:55 PM, Khaled Hosny wrote:
> 
> > On Sun, Apr 07, 2013 at 02:59:32AM +0200, Lóránt Pintér wrote:
> > > Hi,  
> > >  
> > > I'm struggling with the problem of shaping mixed text. Say I have Thai
> > > and English text that I would like to shape. If I put all of it in a
> > > buffer, HarfBuzz chooses a shaper based on the first identifiable
> > > character, and then uses that shaper for the whole text. So
> > > "<thai><english>" gets shaped fine with the Thai shaper, but
> > > "<english><thai>" gets messed up because it is shaped with the default
> > > shaper.
> > >  
> > > I was trying to figure out how Pango does this, but found nothing yet.
> > >  
> > > Is it possible to ask HarfBuzz to identify text runs inside a buffer
> > > (or some other way) that can be shaped with different shapers? If
> > > there was a call that would identify the script (and maybe writing
> > > direction) of each character in the input, then I could split the
> > > buffer at positions where these a different script is used.
> > >  
> >  
> >  
> > You have to split the text runs before passing them to HarfBuzz, etch
> > run should have the same script/language and text direction.
> >  
> > Ideally text should be first itemized into runs with the same script,
> > and further split them into directional run according to BiDi algorithm.
> >  
> > There are of course more subtleties involved, like when using multiple
> > fonts etc.
> >  
> > Regards,
> > Khaled
> >  
> >  
> 
>