Ok, here goes:
When I was installing Nvidia drivers and Bumblebee for my 780m Optimus laptop, the Intel driver somehow made my display undetectable, making X output in the lowest resolution it could (the failsafe resolution). To counter that, I found a guide for making xrandr force my 1080p resolution. That ended up with a script that I configured to start on login:
xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120-hsync +vsync && xrandr --addmode eDP1 "1920x1080_60.00" && xrandr --output eDP1 --mode "1920x1080_60.00"
That works great, but with one hitch: the login screen still has that horrible, low resolution, which of course goes up after logging in. But my question is: How do I run the above script so that the login screen also has a decent resolution?