[arch-general] Subpixels and append mode in Font Config 2.10

[Martin Panter]

Hi all

Yesterday I replaced fontconfig-2.8.0-2 with fontconfig-2.10.1-2, and
I noticed that subpixel rendering was no longer working. I can get it
working again by restoring mode=“assign" in
/etc/fonts/conf.d/10-sub-pixel-rgb.conf, but I would like to
understand why the new package’s mode=“append” does not work, or if
there is a simpler way I could be doing this.

The 2.10 config file has this giant comment and append line, which is
not particularly illuminating for me:

<!--
  This configuration is available on the major desktop environments.
  We shouldn't overwrite it with "assign" unconditionally.
  Most clients may picks up the first value only. so using "append"
  may simply works to avoid it.
-->
<edit name="rgba" mode="append"><const>rgb</const></edit>

It is apparently all a result of this bug, “Don’t overwrite user’s
configurations in default config”:
https://bugs.freedesktop.org/show_bug.cgi?id=17722

I’m not intentionally running any Gnome of KDE configuration, assuming
that’s what they mean by “major desktop environments”. I have verified
subpixels aren’t rendering in Scite (a text editor using GTK 2) using
a magnifying glass :P on the number 7. I also noticed the fonts
changed in Firefox, and “gitk” (which uses TK).

I just removed ~/.fontconfig/ (to no effect), and don’t seem to have
any other files starting with “font” in my home directory, nor
~/.config/ (assuming that’s what $XDG_CONFIG_HOME means). Does anyone
know of any other place that could set the subpixel mode, or prevent
my setting from taking effect? Is there some simple Font Config
program that could help debug this?

Thanks for any help or pointers
-Martin