gnomegtkqtthemes
I noticed whenever I force qt applications to use any GTK theme on Ubuntu 19.10 by adding the line export QT_QPA_PLATFORMTHEME=gtk2 to .profile, the startup time goes from 1-3 seconds to 20+ seconds for vlc and qbittorrent. Why is this and is there anything I can do?
I have ran
sudo apt install qt5ct
and
sudo apt install qt5-style-plugins
You can try to set Java's default look and feel to GTK:
Open a terminal ( Ctrl + Alt + T ) and paste the upper one for openjdk and the lower one for sun java .
gksu gedit /usr/lib/jvm/java-6-openjdk/jre/lib/swing.properties
gksu gedit /usr/lib/jvm/java-6-sun/jre/lib/swing.properties
Follow the comment in that file and remove the hash sign, so it looks like:
# uncomment to set the default look and feel to GTK
swing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel
Save and restart the java app.
Before and after:
The look and feel of Qt5 applications is determined by platform themes and styles. The platform theme is responsible for icons, fonts, etc. and the style controls how widgets are rendered. I think you'll find your application such as Qt Creator is using the GTK3 platform theme as standard.
The problem has occurred since Qt5.7. In this release, the GTK2 platform theme and style was removed and replaced with the GTK3 platform theme. I've recently been in discussion with the Qt developers and it appears there isn't a GTK3 style to complement the platform theme and there are currently no plans to implement this in the future. Therefore, on Ubuntu, the default style is "Fusion" using the GTK3 platform theme.
There are a couple of methods to add a native style as follows:
qtstyleplugins that can be downloaded here. Unfortunately, the GTK2 style is not compatible with the GTK3 platform theme. If you want to use the GTK2 style you will have to use the GTK2 platform theme. This will mean your dialogs etc. do not look native in Ubuntu 17.04. However, you may prefer it to "Fusion".QGnomePlatform available here and adwaita-qt available here. This provides a fully native look and feel when using Ubuntu Gnome.For Qt Creator, I'm not 100% sure if it uses global theme/style locations. You may have to install them in {Qt_installation_folder}\Tools\QtCreator\lib\Qt\Plugins\platformthemes\ and {Qt_installation_folder}\Tools\QtCreator\lib\Qt\Plugins\styles\.
Best Answer
On Ubuntu based Pop OS this same issue is occuring, but only on fresh 19.10 installs and not on 19.04 or 19.10 upgrades from 19.04. So if you had upgraded your system to 19.10 if the issue is not Pop OS specific then you likely won't experience the issue like those on fresh installs.