My app is working fine on an iPad Air 2, and an iPad Pro. It correctly reports the point size and the renderer output size correctly reports the higher pixel values. When I draw to the screen, I have access to all the pixels.
But for some reason it doesn't work properly on an iPhone 6s.
This has a pixel size of 1334 x 750, but SDL2 (2.0.5) is reporting it as 960 x 640.
As a result, everything I draw is surrounded by a black border.
It doesn't seem to be related to retina/high DPI, if I disable all of that, it still incorrectly reports the point size as 480 x 320.
I tried manually creating a window of the correct size, but no dice.