New program for Chromecast a single window

I asked in many forums, if there is an program to chromecast a single window (in my case xournal). As i know (and i searched for a long time), there is no easy way to do that. VLC is not an option, because the result is always a black screen.
I do not need the whole desktop, this is useless for me, because i wanted only to see others, what is happening in one program. On Apple it works fine i saw. It must be possible to realize that in Linux (KDE).