Suggested new mode - Non-Interactive backdrop

[RedBearAK]

I am trying to replicate the function of a macOS utility application called Backdrop.

http://appsfromouterspace.com/backdrop/

The function of the application is very simple. It displays either a single image or a solid color, covering the screen (but not in any special "fullscreen" mode), creating a "backdrop" that you can slip in between other windows using the Alt+Tab task switcher. It's purpose is to just separate one or more windows from all the other clutter on your screen, so you can focus or perhaps take a clean screenshot for a tutorial or whatever.

Importantly, the window that Backdrop displays is non-interactive. You can quit the application with Cmd+Q just like any other Mac application, or quit from the menu bar. But otherwise it doesn't respond to the mouse or the keyboard. It won't quit just because you pressed "Q" or "Escape" for instance. And it's not a general image viewer. You set one image in the preferences for it to display, and it won't change just because you hit the spacebar or arrow keys.

If the macOS menu bar is not hidden, it won't overlap the menu bar, but if the menu bar is auto-hidden it will cover the whole screen. I think the app actually always sets its display size to the full dimensions of the monitor, but it lives in a layer underneath the menu bar so it won't cover the menu bar. But it doesn't use a true "fullscreen" mode that would stop it from being a part of the normal stack of windows in the Alt+Tab stack. That's what makes it so useful as a backdrop between other applications.

I managed to create something using the ImageMagick "display" command that sort of does what I want, but it's a very hacky thing made of two different .desktop files and a shell script. And I can't find any way to get rid of the standard window titlebar and have it just show a solid color across the screen with no window decorations, like what happens with feh -x.

I've looked all over the world of Linux image viewers and feh is by far the closest I have seen to something that could accomplish the same task as Backdrop for Mac. Feh already has the ability to create a borderless window. It already has incorporated several different display modes. It just needs a way to be told to be non-interactive to everything except the standard "quit" command Ctrl+Q, and to be maximized to fill the screen but not in the special "fullscreen" mode that interferes with access to panels and docks and other windows.

Any chance this could be implemented?