[HarfBuzz] The canonical ordering of hamza marks

[Khaled Hosny]

On Sat, Sep 01, 2012 at 06:40:40PM -0400, Behdad Esfahbod wrote:
> On 08/26/2012 07:15 PM, Khaled Hosny wrote:
> > Hi Behdad,
> > 
> > I just noticed that hamza above and below marks (U+0654, U+0655), are
> > reordered after Arabic vowel marks because they have much higher
> > combining classes, 230 and 222 (the "generic" combining class above and
> > below, respectively), which breaks mkmk positioning.
> > 
> > I tried to make a patch to handle them like the shadda, but I'm not sure
> > how safe it is with such generic combining classes.
> 
> Khaled,
> 
> Given that there's a few handfuls of Arabic marks with 220/230 ccc, can you
> help me figure out what the expected behavior is, in respect to the main marks
> and shadda?  I can try to implement that after.

Ideally, I think hamza and madda should come first, then shadda, then
the vowel marks then everything else:

* hamzat and maddat: U+0653-U+0655, U+065F, U+0674, U+06E4
* shadda: U+0651
* vowel marks: U+064B-U+0650, U+0652, U+0656-U+065E, U+08F0-U+08F2

Regards,
 Khaled