bug#32210: Support medium weighted fonts

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> I don't think this is the only place.  For example,
> XG_WEIGHT_TO_SYMBOL looks also relevant.

Interesting...

#define XG_WEIGHT_TO_SYMBOL(w)                  \
  (w <= PANGO_WEIGHT_THIN ? Qextra_light        \
   : w <= PANGO_WEIGHT_ULTRALIGHT ? Qlight      \
   : w <= PANGO_WEIGHT_LIGHT ? Qsemi_light      \
   : w < PANGO_WEIGHT_MEDIUM ? Qnormal          \
   : w <= PANGO_WEIGHT_SEMIBOLD ? Qsemi_bold    \
   : w <= PANGO_WEIGHT_BOLD ? Qbold             \
   : w <= PANGO_WEIGHT_HEAVY ? Qextra_bold      \
   : Qultra_bold)

If we look at

https://abi-laboratory.pro/?view=headers_diff&l=pango&v1=1.36.5&v2=1.36.6

we find

* @PANGO_WEIGHT_NORMAL: the default weight (= 400)
* @PANGO_WEIGHT_MEDIUM: the normal weight (= 500; Since: 1.24)

so Pando has also grown a MEDIUM in addition to NORMAL...  and we don't
have PANGO_WEIGHT_NORMAL.

> And there are other places in the sources that only support subsets of
> all the weights.  If we want to make them more fine-grained, we should
> make them all consistent, as much as possible, modulo the limitations
> of the toolkit.

Yup.  

> For example, Someone™ should verify that the problem described above
> is not some inherent GTK limitation.

If we look at

https://emacs.stackexchange.com/questions/32377/selecting-correct-font-weight-variant-linux

people seem to be instructing Emacs to use the sizes adjacent to Emacs
normal/medium to actually get the weights they want, and then it works.
Also see bug#28351 (which I've merged with this one).

But is this something we want to tweak before Emacs 27, or should it
wait for Emacs 28?  

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no