Looking at the most common monitor resolutions at Steam to see what it would take to get a 640x360 UI to upscale without shrinking or distortions, things mostly seem simple enough.
1st, 2nd, and 4th most common resolutions are straight upscaling. A 20 pixel border top and bottom for 16:10 displays (3rd and 7th most common) and a 60 pixel border left and right for 3440x1400 displays (5th most common).
But what in hell are 1366x768 displays?! (6th most common.)
Why does this exist?
