I’ll be setting up an RPi 4 soon. Unfortunately, I have no choice but to pair it with a 4k display. I have to have Raspbian’s relatively new “pixel-doubling” option so that I can integer scale 1920x1080 to 4k.
Does Lakka support this feature? I have to have it OS-wide, not just within RA. In my case, it’s the difference between a crisp, pixel-perfect image and a blurry, migraine-inducing one.
RetroArch scales cleanly to 4K. Lakka doesn’t do anything but RetroArch, so there’s not really any other part of the OS to interact with directly.
Thanks! I’m a newb to mini-distros like this, but that answers my question. Dual-booting Lakka and Kodi might make sense for me as I need both retro-gaming and multimedia playback and don’t really want to compromise by using RetroPie. I’ll do my homework. 
Just turn on “Integer Scaling” in the RA video options. That gives you pixel doubling.
i would also recommend forcing your pi to output at 1080p as it’s going to be a slideshow at 4k
If RetroArch is a slideshow at 4k on a Pi 4, I won’t be able to use it at all. My reason for needing integer scaling is how awful 1080p typically scales on a 4k display. Blurry upscaling literally makes me sick. I’ll just repurpose this Pi for minidlna and give it to my parents.
1080p will scale perfectly on 4k since it’s a 2x integer scale of it. i believe retroarch defaults to bilinear filtering on so you’ll want to turn that off, but it looks perfectly crisp to me at 1080.
I’m running an RPi4 on Lakka on a 4K TV and echoing the others here - performance was unusably bad until I reduced the resolution to 1080p. It looks fine in 1080p. I’m having a bevy of other problems with Lakka, but performance (other than N64) hasn’t been one of them ever since that change.
I’ve logged a bug with Lakka about it:
requesting a “max resolution” optional setting for low-power devices so that it would automatically switch resolutions as it does currently except it wouldn’t go above 1080p.
Hey, I think this has more to do with performance at higher resolutions. For example, using an rpi3 at 1080p shows just a bit of FPS dip at the GUI while default settings, but runs fine at 960x540. The problem is that the default scaling used by the system in that case is bilinear.
The same issue occurs if you try to scale a display using xrandr with default settings, but can be worked around with a very simple fork of that. Of course since lakka doesn’t seem to use xorg or to have xrandr, I can’t really try that here, but it seems like the solution would be similarly applicable.