Comment 6 for bug 1287341

Seb wrote in an email:

"In fact discussing a bit on IRC and looking at
https://bugzilla.gnome.org/show_bug.cgi?id=698284 it might not be as easy

Xorg/the hardware doesn't give us a way to determine that an input
system is linked to a screen. It's easy enough when you have 1 of each
to match them, it's less trivial if you have e.g 2 screens and an input
device. We can probably come up with some heuristics for common cases
(like assuming that if you have a laptop screen and an external monitor
and a touch input, that's probably the laptop screen one) but not sure
how well that's going to work..."