Onboard virtual keyboard unusable (because of too small) on login screen

This is a long standing issue with GtkSocket in unity-greeter.
https://bugs.launchpad.net/ubuntu/+source/gtk+3.0/+bug/1572331

I did provide a patch at
https://bugzilla.gnome.org/show_bug.cgi?id=765327
but there doesn't seem to be any interest in having this bug fixed.

I think what we should do is ask Ubuntu to accept the patch for their gtk+3.0 package.

@Francesco, would you be able to provide a debdiff with the patch for bug #1572331? Else I'll try it.

There might be another workaround, but I haven't tested that recently:
sudo -i # get root
xhost +SI:localuser:lightdm # Allow the user lightdm to create a connection to the X server
su lightdm -s /bin/bash # Switch user to lightdm
gsettings set org.gnome.desktop.interface text-scaling-factor 1.0

That would presumably prevent unity-settings-daemon from picking scaling-factor 2.0 and stick with 1.0. Not ideal on a HiDPI screen, but Onboard should at least be able to use the whole screen width.

I had this same issue on Debian testing. This workaround did not work (strange error of directory access).
By the way, I found this point :
LightDM has options in /etc/lightdm/lightdm-gtk-greeter.conf :
[greeter]
keyboard=onboard --layout='/usr/share/onboard/layouts/Phone.onboard'
keyboard-posistion = 50,center -0;100%,25%
The "100%" is for using the whole screen width...

Thanks a lot for this nice on-screen keyboard !