I have a simple SDL2/OpenGL (ES) 3D test program which runs on Windows, Linux (x86 and Raspberry Pi), Mac OSX and Android. However it didn’t run on iOS and I’ve been struggling to understand why. Turns out that it needed the addition of a glViewport() call; now it runs the same as on the other platforms.
I’m guessing that this isn’t deliberate, and that probably there should be a call to glViewport() somewhere in SDL2 when running on iOS so that all the platforms behave the same way. Maybe this could be looked into, if only to spare somebody else the grief it has given me!