[HarfBuzz] Arabic and diacritics: problems with Arial and Arial Unicode

[Grigori Goronzy]

Hi,

I'm having some odd issues with Arial and Arial Unicode. When I use
these fonts to render Arabic text with diacritics, there are "gaps"
inside the words. The diacritics have non-zero advance, this seems to
cause it. Are these fonts just buggy or am I doing something wrong?
There are no such problems with other fonts, such as DejaVu Sans.

What is the correct way to render all glyphs that belong to a certain
cluster? I'm a bit at loss at the moment.

Best regards,
Grigori