fontique: generic families (Fedora/KDE)

[dhardy]

Fontique does not correctly detect UI fonts on KDE 5:

GenericFamily::SystemUi:
Cantarell
Cantarell
Cantarell

GenericFamily::UiSerif:

GenericFamily::UiSansSerif:

GenericFamily::UiMonospace:

GenericFamily::UiRounded:

XDG_CONFIG_HOME is not set, while XDG_CONFIG_DIRS is, but does not point to any font configuration, so my best guess is that we must test XDG_CURRENT_DESKTOP=KDE(:.*)?, then parse $HOME/.config/kdeglobals.

Excerpt from the latter:

[General]
ColorSchemeHash=0be804dba87e3512aeb4be3d78ed981f59f0f2f4
XftHintStyle=hintslight
XftSubPixel=none
fixed=Noto Sans Mono,11,-1,5,50,0,0,0,0,0
font=Noto Sans,12,-1,5,50,0,0,0,0,0
menuFont=Noto Sans,12,-1,5,50,0,0,0,0,0
smallestReadableFont=Noto Sans,10,-1,5,50,0,0,0,0,0
toolBarFont=Noto Sans,12,-1,5,50,0,0,0,0,0

This is:

• The family name
• Size ("points", so presumably we just multiply by 96/72 = 4/3 to get dots-per-Em)
• ... requires investigation

The hinting (none/slight/medium/full) & sub-pixel rendering (none, rgb, bgr, vrgb, vbgr) info is likely best ignored since (a) it is beyond the scope of Fontique and (b) is rasterer dependent.

[xorgy]

Thanks for having a look at this, there's a significant rework required to make Fontique and Parley handle fallback and generic families well on various platforms. FontConfig is pretty sprawling, and the information in the config files is simultaneously very detailed and missing important details.

[dhardy]

I get the impression that fontique (and anything attempting to do this job in a cross-platform manner) is going to end up as a pile of hacks. I think most of the time there isn't even good documentation, besides source code (where available)?

Let me know if you want further testing on this platform.

[xorgy]

I am personally interested in DE/system font settings, but I'm not 100% sure where they belong in the Fontique/Parley ecosystem. If you have some ideas or example programs for resolving these I'd love to see it.
Subpixel rendering settings are not completely useless, but there is a question as to when to override monitor defaults (from XRandR on X11 for example) for simple layouts, and how to deal with advanced generalized subpixel layouts like those supported by FreeType2; and again as you acknowledge these don't necessarily belong in Fontique (but maybe they belong near Fontique).

[valadaptive]

I think the root cause of both this and #323, after looking into the latter a while back, is that fontique currently doesn't actually implement fontconfig matching, partially or fully, it just does a very rough approximation of it.

Is there a reason not to just FFI into fontconfig itself? The library should be present on all the platforms that the config files themselves are, and it doesn't seem any less safe than calling into DirectWrite and CoreText on Windows and macOS.

[dhardy]

Is there a reason not to just FFI into fontconfig itself? The library should be present on all the platforms that the config files themselves are, and it doesn't seem any less safe than calling into DirectWrite and CoreText on Windows and macOS.

For one thing, fontconfig doesn't actually match all those fonts anyway:

$ for g in serif sans-serif monospace cursive fantasy system-ui ui-serif ui-sans-serif ui-monospace ui-rounded math emoji fangsong; do echo "$g:  $(fc-match $g)"; done
serif:  NotoSerif-Regular.ttf: "Noto Serif" "Regular"
sans-serif:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
monospace:  NotoSansMono-Regular.ttf: "Noto Sans Mono" "Regular"
cursive:  Z003-MediumItalic.otf: "Z003" "Medium Italic"
fantasy:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
system-ui:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
ui-serif:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
ui-sans-serif:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
ui-monospace:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
ui-rounded:  NotoSans-Regular.ttf: "Noto Sans" "Regular"
math:  STIXTwoMath-Regular.otf: "STIX" "Regular"
emoji:  NotoColorEmoji.ttf: "Noto Color Emoji" "Regular"
fangsong:  NotoSans-Regular.ttf: "Noto Sans" "Regular"

The common generic families (except fantasy) resolve to something, as do math and emoji, but none of the ui variants do.

Those family names are documented here for the web. I tested in Firefox too and didn't get matches (other than Noto Sans) for those ui fonts.

This OS is Fedora 42.

[dhardy]

Trying to dig a little deeper, https://github.com/tmcw/systemfontstack has some good info.

Testing CSS in Firefox, system-ui appears to resolve to "Noto Sans" (correctly), while all ui-* generic families appear to resolve to "Noto Serif" (incorrect and the same behaviour as using junk names; this is slightly odd since fc-match defaults to "Noto Sans" instead).

The ui-* generic families are not widely supported by browsers: https://caniuse.com/extended-system-fonts

---

So I would tentatively recommend:

• The resolution of SystemUi to Cantarell as reported here is a bug.
• Drop GenericFamily::Ui* variants due to lack of widespread support (and them mostly being equivalent to serif, sans-serif etc. anyway)

[dhardy]

fc-match system-ui returns "Noto Sans", while fontique's parsing of configuration does not discover this binding. What fontique does discover is this:

parse_config: path=/etc/fonts/fonts.conf
[...]
parse_config: path=/etc/fonts/conf.d/31-cantarell-vf.conf
alias: family=system-ui, prefer: ["Cantarell"]
parse_config: path=/etc/fonts/conf.d/31-cantarell.conf
alias: family=system-ui, prefer: ["Cantarell"]
[...]
parse_config: path=/etc/fonts/conf.d/60-latin.conf
alias: family=system-ui, prefer: ["Cantarell", "Noto Sans UI", "Segoe UI", "Segoe UI Historic", "Segoe UI Symbol"]
[...]
parse_config: path=/etc/fonts/conf.d/69-nonlatin.conf
alias: family=system-ui, prefer: ["Noto Sans Arabic UI", "Noto Sans Bengali UI", "Noto Sans Devanagari UI", "Noto Sans Gujarati UI", "Noto Sans Gurmukhi UI", "Noto Sans Kannada UI", "Noto Sans Khmer UI", "Noto Sans Lao UI", "Noto Sans Malayalam UI", "Noto Sans Myanmar UI", "Noto Sans Oriya UI", "Noto Sans Sinhala UI", "Noto Sans Tamil UI", "Noto Sans Telugu UI", "Noto Sans Thai UI", "Leelawadee UI", "Nirmala UI", "Yu Gothic UI", "Meiryo UI", "MS UI Gothic", "Khmer UI", "Lao UI", "Microsoft YaHei UI", "Microsoft JhengHei UI"]
[...]

No installed fonts contain "UI" in the name however, nor is "Noto Sans" listed first. So I don't understand this.

Clearly many more fontconfig rules are skipped (including non-generic family name substitutions), but ripgrep doesn't find anything related to the above.