autohotkey - Set Scaling of individual applications in Windows

I occurs to be that I want any app I'm not looking at to be scaled down (to say 100%), but the one in focus to be scaled up (to 200%). This would both make maximal use of my hi-res laptop screen for peripheral vision and give my eyes a rest for the focused task.

I'm not talking about per-application, like Set DPI of individual applications in Windows

I want any app that supports scaling to be re-scaled when I'm looking at it.

The magnifier sucks, in case you thought of that :)

I'm supposing it needs to be an autohotkey (AHK) script.

Thanks, Martin.