Found the problem, while "minimizing" the problem:
The order of these two functions:
while(App.IsOpened())
{
FEvent();
FDisplay(1.f, 1.f, 1);
}
Makes it so that FDisplay is never called. If I call FEvent(), FDisplay() isn't called, and nothing is displayed. If FDisplay() is called first (and FEvent() is slightly tweaked, making a FDisplay call), everything works fine. I should have noticed that before... Anyway, thanks for the help!