There are two graphic stacks on Ubuntu. You can choose which one to use using the cog icon on the login screen. The older stack uses the X11 protocol with xorg as the display server. The newer stack uses Wayland as the protocol and various compositors - a separate one for each desktop environment - as both display server and window manager. Wayland has been in development for a long time now, but there are still areas where the protocol and the implementations have problems. Screensavers are one of these areas, so to the best of my knowledge what you want to do can't currently be done on wayland (I wouldn't mind being proven wrong on that, I'm using Xubuntu (XFCE-desktop) which doesn't yet support Wayland, so my knowledge of Wayland is mostly theoretical).
On X11 one of the best known screensavers is 'xscreensaver'. It's modular with a background process that takes care of when to blank or un-blank the screen and reacting to hot-keys, a program to make settings to the screensaver ('xscreensaver-demo'), and a lot of small programs called display hacks that have no purpose but to show some graphics on the blanked screen. You can write your own display hack or use a program as a display hack that can be told to make it's output into a specific window. To do so you edit the configuration file for xscreensaver ('~/.xscreensaver') and add the new program to the line that starts with 'programs:' (yes, it's all one line with lots of escaped line-endings ...). For example, I added 'mpv' (a video-player controlled from the command line) to the programs like so:
Code:
...
programs: \
mpv --really-quiet --no-stop-screensaver \
--loop=inf --fs --no-audio \
--wid=$XSCREENSAVER_WINDOW \
$HOME/Videos/'TSV.mkv' \n\
maze -root \n\
...
As you can see one program can be spread over multiple lines by putting escaped line-ending to split up long commands; the part describing one program ends with '\n\'+line-end (so 'maze -root' is the command for the next program in the list).
The important thing here is '--wid=$XSCREENSAVER_WINDOW'. The option '--wid=' tells mpv to write to the window with the id given after the option and '$XSCREENSAVER_WINDOW' is a variable passed from xscreensaver to a hack that contains the id of the undecorated window xscreensaver puts over the display to hide it's content.
The other half of my solution is conky. conky is a very configurable status display program. It has an option '-w' or '--window-id=' that does the same thing as the '--wid=' of mpv. Configuring conky is ... complex ... to say the least, so look for tutorials and examples on the net - there are lots of them.
Holger
Adv Reply
Bookmarks