I'm not sure if this is a Calibre issue or maybe a dependency issue. I recently upgraded to XUbuntu 17.10 which uses Qt 5.9. I have set the CALIBRE_USE_SYSTEM_THEME variable for calibre to use the Gtk/XFCE theme which in my case arc-theme. Note, all my other Qt5 applications including Qt5 Designer, work correctly while using the GTK theme.
A pure binary install from the script as provided on the website here:
https://calibre-ebook.com/download_linux doesn't work. The theme is completely broken and there are parts of the menus which I can't access. I initially got this error on Calibre 3.0, and then I uninstalled that, and installed Calibre 3.12, both giving the same error on the system as:
Code:
QGtkStyle could not resolve GTK. Make sure you have installed the proper libraries.
Though, I tried a binary install from the Ubuntu repos for Calibre 3.7.0 which works perfectly fine, and adheres to the environment variable to use my GTK theme.
I hope this issue gets fixed sometime.
tempura