Discussion for #425742

I would be very happy if the Breeze theme for KWin offered an option for transparency, allowing Windows Aero style blur for the background. It's one of the main missing features for the default theme, due to which I've been using my own Aurorae based theme (Freeze) just to work around this limitation.

When you go to System Settings - Appearance - Application Style - Window Decorations - Theme, click the little icon with the pen over Breeze (Edit Breeze Theme), there should be a slider to allow adjusting the transparency. At the default value of 0 the behavior remains unchanged... when above 0, the background of the decoration should become transparent and use the blur effect behind it. I attached a screenshot from my modified Freeze theme as a close example of how this should look like (50% transparency).

Even better would be for the Colours KCM to allow RGBA values to be specified, rather than just RGB, thus allowing transparency to be fed to any theme.