transparent windows under linux

https://www.google.bg/search?q=transparent+windows+linux+howto&ie=utf-8&oe=utf-8
https://wiki.archlinux.org/index.php/Xcompmgr
https://wiki.archlinux.org/index.php/Per-application_transparency
compiz + composite/compositing engine extension of X11 enabled + A;t key and mousewheel up/down

https://forum.qt.io/topic/14685/how-to-create-transparent-window-in-linux
http://stackoverflow.com/a/9380468
http://cupugila.blogspot.bg/2012/08/make-ubuntu-unity-window-look.html
https://forums.linuxmint.com/viewtopic.php?t=81715

etc.