https://bugzilla.redhat.com/show_bug.cgi?id=1645763
--- Comment #18 from Marek Kašík <mkasik(a)redhat.com> ---
The visible color fringing is caused by cairo using FT_LCD_FILTER_LEGACY as a
default lcd filter. It was chosen when the code was introduced to cairo (see
https://bugs.freedesktop.org/show_bug.cgi?id=10301 and
https://gitlab.freedesktop.org/cairo/cairo/commit/7a023a62f7517ad0d54f4d5...
for more details).
You can reproduce this by running:
pango-view --backend=cairo --dpi=134 --font="Cantarell Regular 11"
--text="4444"
or by running:
ftview -r 134 -m "4444" 11 /usr/share/fonts/cantarell/Cantarell-Regular.otf
and pressing "D" and then "L" until you get legacy filter (the
gnome-calculator
uses 1.4x font scale and it was probably on 96dpi screen => ~134dpi).
Question is what to do with it. Possibilities are:
1) Ask cairo maintainers to change the default lcd filter (to which one? I
would prefer FT_LCD_FILTER_LIGHT but there is FT_LCD_FILTER_DEFAULT in freetype
so it should be it probably)
2) Add a configurable option to Gnome and let users configure it as subpixel
rendering itself
3) Select a filter in freetype code by default (Which one? And others might
prefer to configure it still.)
4) Use Harmony (it does not use LCD filters)
I would go with number 1 for now.
Btw, you can change the lcd filter by setting e.g. "Xft.lcdfilter: lcdlight" in
"~/.Xresources" for now (see
https://wiki.archlinux.org/index.php/font_configuration for additional info).
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