Re: Ligature support

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> We have font-shape-gstring.  If the font being used doesn't have a
> ligature for the character sequence we pass to it, that function
> returns nil, and we then display those characters "normally".  Isn't
> that enough?

That's what I thought the design here was originally -- but that's not
what's happening in general in Emacs.  If I instrument
font-shape-gstring and start "emacs -Q", that function is never called.
It's not until I insert something that we've set up something in...
composition-function-table?...  that the function is called and harfbuzz
is consulted.  (You can confirm by setting a breakpoint on
hbfont_shape.)

I thought we'd just send all the text through hb_shape_full, and it
would handle all this stuff.  But we don't -- we only send a very small
subset of the strings through that function, as far as I can tell.

>> So...  we need...  to parse them more to get all the ligature data out
>> of them and then...  put it in a ... char table range?  How all this
>> connects is very vague to me.  😀
>
> As I say above, I'm not sure I understand the goal of this, given what
> we have already.

The goal is to send all text that represents ligatures (in the current
font) through font-shape-gstring.

-- 
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   bloggy blog: http://lars.ingebrigtsen.no