So, for a university project, I'm building an arcade cabinet and one of its features is the ability to unlock more gametime via QR code. With Android and Python I was able to make it work by pausing the RetroArch process with pkill -stop.
Now I want to display a message (or image) on top of RetroArch saying something like "Insert Coin", however, after many hours of research, I still haven't found a proper way to do it. Fbi runs on the terminal behind RetroArch and so do the demo programs located on /opt/vc/src/hello_pi.
Is there any way to achieve this, either by overlapping a message or even minimizing the RetroArch process?