If your preferred video resolution is not being detected, or you want to use a non-standard resolution in windowed-mode, then you will need to edit the config.ini.

Either add or change the following tags in the [refgl] section.

config.ini
--------------------------------------
[refgl]
xf86vidmode=0
xsize=1920
ysize=1080
windowmode=1

Can we pin this one? It's useful info.