Further to my earlier post here on this same matter, I’ve found an even better way of fixing KDE (Qt) fonts thanks to this openSUSE guide.

Just run “kcmshell4 fonts” and turn on antialiasing and full hinting and sub-pixel rendering. Hey presto, nice looking fonts in Calibre, VirtualBox, Chrome etc.

Essentially it creates ~/.fonts.conf with the following content:

<?xml version='1.0'?>

<fontconfig>
 <match target="font">
  <edit mode="assign" name="rgba">
   <const>rgb</const>
  </edit>
 </match>
 <match target="font">
  <edit mode="assign" name="hinting">
   <bool>true</bool>
  </edit>
 </match>
 <match target="font">
  <edit mode="assign" name="hintstyle">
   <const>hintslight</const>
  </edit>
 </match>
 <match target="font">
  <edit mode="assign" name="antialias">
   <bool>true</bool>
  </edit>
 </match>
</fontconfig>