I’m not sure about android, because it may not be supported well by the android OS, but if you are using a windows based system, you should be able to open multiple windows on the different screens opening multiple viewports on the separate screens.
I’m pretty sure Android doesn’t support multiple displays though.
I have an android tablet and a projector or tv. I would like to use a vga, dvi or hdmi cable to connect both devices, and use the tablet as my main input device and the projector or tv as the “output”. Like having a virtual controller on the tablet and the game itself without any visual-controls on the screen.
Any way to achieve this technically?
AFAIK no out-of-the-box solution on UE4 side. IMO your best bet would be to explore the Android Media Router interface, actually the Android way to deal with multi-screen. You could explore the Android Cast API too. GLSurfaceView seems to be supported but I would expect either latency or rendering rate issue with the engine. In any case some hard work in perspective with UE4 integration but I would be amazing to have such module!