How to show a "black" screen over an open application?

Question

linux

Good afternoon, I have a computer running Linux Mint 19. A full-screen presentation is running on the computer, all this is shown on the projector.
There is a task, on top of this application, display a "black" square in order to "turn off" the projector. And when you need - leading our button, close the "black" square and we have a presentation in front of us.
As an option, make a black desktop, without the bottom panel. And on command, start the presentation - but it takes time to load. I would like a faster way.
Is there some kind of command in the console - to display a black square on the screen over the application, and then remove it?

Answer 1

It may be more convenient to disable and enable screen output altogether.
The xrandr -q command can list all connected video outputs. To turn off output to VGA
-1, for example, you can use the A command
to turn it on brightness And try to change it to zero to "turn off".
xrandr --output HDMI1 --brightness 0.0