I have been trying to setup Retroarch on my 4K TV. However the GUI will always launch in 720p and games run at that resolution also. This is on a Win 10 system with a GTX 980.
I would like to run it at 2160p but have had no success so far. I’ve been at it for hours now playing around with the settings.
I’ve tried setting the aspect ratio to custom and setting the viewport resolutions to 3840 and 2160 but am still stuck at 720p.
Could someone please give me some advice on what to do?
The only settings that should matter in this case are in your retroarch.cfg: video_fullscreen_x and video_fullscreen_y. Set them each to “0” and RetroArch should scale to your resolution.
I’ve tried that but it’s still stuck at 720p.
video_fullscreen_x = “0” video_fullscreen_y = “0”
I’ve also tried these settings:
custom_viewport_width = “3840” custom_viewport_height = “2160”
No luck yet 
I managed to fix the GUI by setting video_fullscreen_x and video_fullscreen_y to 3840 and 2160 respectively in retroarch.cfg
For the games it still ran at 720p so in the cfg files for the cores I changed that setting there also.
Now everything is in 4K! Just have to play with shaders now.