bug#50951: 28.0.50; Urdu text is not displayed correctly

[Rah Guzar via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Hi Eli,
Eli Zaretskii <eliz@gnu.org> writes:

> It is unclear to me why this conclusion.  Emacs uses HarfBuzz, and the
> only factor that could affect that, apart from selecting the font, is
> the setting of the current-iso639-language variable, which AFAIR
> Rahguzar tried setting with no success.

At your suggestion, I tried hb-view and it renders Noto Nastaliq fine.
Similarly Libre Office which also uses harfbuzz as far as I understand,
also renders it fine. Which is why I said that the problem is limited to
emacs. My understanding of font rendering is non-existent but visually
what seems to happen is that emacs displays all the individual atoms
(glyphs?) but it doesn't know how to position them relative to each
other so they overlap and obscure each other. This positioning is
especially tricky in Nastaliq fonts since it can require moving all of
up, down, left, right. The big fonts that emacs render correctly, take
care of this by prepackaging all these combinations of characters that
require anything other than right to left movement as separate shapes.

Sorry, if this reads as confused.

> My conclusion from this is that Noto Nastaliq is not a good font for
> Urdu.

On an aesthetic level, I tend to agree. But linux distributions package
very few Urdu fonts and it tends to be one of the few.