[HarfBuzz] Unicode vs glyphs

[Eduardo Castiñeyra]

Hi,

I do not understand why the function hb_shape returns glyphs instead of 
unicode characters. I understand that different fonts could have 
different glyph indices for a given symbol, but Unicode does not depend 
on the fonts, so it would be more usefull to return Unicode indices.

For instance, I used fribidi in the past and it returned the visual 
string in Unicode format. I think that hb_shape does pretty the same 
thing. The only reason I imagine is that not all the glyphs may have an 
index in the Unicode table, so it would be imposible to represent them 
all as Unicode indices, but I don't know whether it is true.

Is there a way to convert the given glyphs into Unicode indices?

Is there any literature about layout processing for not having to ask 
these kind of questions in the list? I'm very lost on what to expect 
from i18n libraries.

Thanks a lot.