I have changed my GDM3 background by changing ubuntu.css.
#lockDialogGroup {
/* background: #2c001e url(resource:///org/gnome/shell/theme/noise-texture.png);
background-repeat: repeat; }*/
background: #000000 url(file:///usr/share/plymouth/themes/trinity/chrono-trinity1920x1080.png);
background-repeat: no-repeat; }
This kind of works, but now the image is displayed in the center of my multi monitor setup.
How do I change this so the image is displayed as a background on every monitor separately instead (like a regular wallpaper)?
This is more of a hack than a clean solution. Is there one available ?
My suggestion is to use Gimp to create an image that spans the 3 monitors using the same layout as your monitor.
It is just a matter of 5 minutes, if you know Gimp, a little else, if you don't.
This way, you can use whatever you want as wallpaper for each monitor. You are not obliged to use the same image. The final image size is in green.