bug#32210: Support medium weighted fonts

[Lars Ingebrigtsen]

Carlos Pita <carlosjosepita@gmail.com> writes:

> Many programming fonts are designed for hidpi devices and look pretty
> bad (too thin and "diffused") in their default weight in antialiased
> settings with standard resolution screen.
>
> Nevertheless a number of fontsets provide medium and/or demibold variants in
> between the regular one and the bold one. For example, the medium
> SauceCodePro (based on SourceCodePro) looks much solid than the regular
> variant.
>
> Now, the problem is that, no matter how emacs font is configured
> (xresources with xft or gtk descriptor, customize-face, the standard
> gtk dialog launched from the menu) medium is taken as an alias for
> normal/regular and you have to jump from regular to demibold.

I think this is the culprit:

static const struct table_entry weight_table[] =
{
  { 0, { "thin" }},
  { 20, { "ultra-light", "ultralight" }},
  { 40, { "extra-light", "extralight" }},
  { 50, { "light" }},
  { 75, { "semi-light", "semilight", "demilight", "book" }},
  { 100, { "normal", "medium", "regular", "unspecified" }},
  { 180, { "semi-bold", "semibold", "demibold", "demi" }},
  { 200, { "bold" }},
  { 205, { "extra-bold", "extrabold" }},
  { 210, { "ultra-bold", "ultrabold", "black" }}
};

We define "medium" the same as "regular", but there are many fonts that
have both "regular" and "medium" variants, if I understand things
correctly.  Googling around a bit, it seems that most pages that
describe these things put "medium" at the halfway point between
"regular" and "demibold", which would mean a value of 140 for Emacs.

For instance:

https://www.quora.com/What-is-the-difference-between-Medium-Demi-and-Semibold-fonts
https://cssreference.io/property/font-weight/

Those are from a web/TrueType perspective, though.

Anybody have any thoughts on this issue?  The medium/regular
non-distinction in Emacs seems to crop up here and there, so it's a
problem in practice.

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