I newer have succeeded with this. It expand, but it renders in that higher resolution. There seems to be no way to render in lowres and 2D-scale to fullscreen (on linux at least). That’s silly, rendering in lowres + 2D-scale must be much faster than rendering in highres - Optimally we should be able to change render res runtime and still scale to the same size - so we can adopt resolution to maintain descent framerate.
Even more optimal if we can except scenes from scaling - ie render a owerlay scene with only a few shadeless object and blt text in highres but all else in lowres and scale to same size.
I have planed to make a test with rendering to a texture and display that as scaled up background in an overlay scene. But I suspect that will introduce some unnecessary overhead eating up the benefit if it’s at all possible.