You can specify an output that you would prefer to be fullscreen.
If this value is NULL, it's up to the compositor to choose which
display will be used to map this surface.
If the surface doesn't cover the whole output, the compositor will
position the surface in the center of the output and compensate with
black borders filling the rest of the output.
set the window as fullscreen on a monitor
Make the surface fullscreen.
You can specify an output that you would prefer to be fullscreen. If this value is NULL, it's up to the compositor to choose which display will be used to map this surface.
If the surface doesn't cover the whole output, the compositor will position the surface in the center of the output and compensate with black borders filling the rest of the output.