I tried that font and text with hb-view and the output I get is
identical to m17b.
hb-view is nifty! I wasn't sure if it would work for me (because I haven't set my terminal to show unicode, etc.). But even with the older Harfbuzz 1.0.3 that I have, hb-view gave this:
https://i.imgtc.com/d1N177Z.png
I am impressed. That shows the correct rendering of
નમસ્તે. (I just blindly pasted
નમસ્તે as the second argument and hit enter, my terminal doesn't even show the pasted text. But the hb-view rendering is correct.)
If I pass a wrong script to HarfBuzz (e.g.
--script=latn), I get the same broken output you see in Emacs. So I’m
guessing something is not correctly working in script itemization. Most
likely the FIXME in uni_script(), or the FIXME above the call to
hb_buffer_guess_segment_properties().
I am not a C developer. But hopefully this information would help you to fix the Harfbuzz integration with Emacs.
I am surprised that the rendering of Hindi नमस्ते using Harfbuzz in Emacs is correct, while the rendering of Gujarati
નમસ્તે is not, when in fact the two scripts are so similar to each other. [Fun fact: Most of Gujarati script if superimposed with a line at the top will look like valid Hindi. You can see that in the case of
નમસ્તે
vs
नमस्ते
:) ]
