[feature] screen swap in landscape mode

[cybardev]

In landscape mode, the DS screens are either stacked vertically or laid out side-by-side horizontally. It would be much nicer if I could just use a screen swap button (UI element in overlay + mappable on controller) to swap between screens while showing only one big screen at a time.

Ignited has it, partially, which works for my use case.

[gingerbeardman]

+1 for this

My use case is playing a game that only uses one scren for gameplay. I don't want to see the other screen and would appreciate the single screen taking up the whole display.

eg. MaBoShi DS (which is also a game that uses the DS in "book" orientation)

https://www.youtube.com/watch?v=MiVbBi0jdhw