One feature that I have become very fond of, is having Border Overlays while emulating old handhelds that have a relative low native pixel resolution. Gameboy/Color and the Sega Game Gear. On the Gameboy Color I have a purple Gameboy Color Border Overlay surrounding the actual image (I use Integer Scale, Custom Aspect Ratio and a screen size that is 5x the native resolution, 800x720).
I personally don’t like to enlarge the image too much on those older handhelds because the pixels then becomes way too big, Border Overlays can help by making a smaller image both stylish and seamless in my opinion.
This is all well and good on both of my 1080p screens, but sooner or later I’m going to migrate to a 4K TV, and than this setup becomes a bit more troublesome. Since my RetroArch setup is configured to display 5x the native resolution to fit the Border Overlays (I have an overlay scale of 1.25), to my limited knowledge there is no way to automatically turn the Custom Aspect Ratio Width- and Height from 5x to 10x when RetroArch detects that I’m now have switched screen resolution from 1080p to 2160p and vice versa.
Maybe there is an automated solution for this, but I haven’t found it yet, so I would need some guidance regarding this issue.