Workaround for Problem Mirroring Displays using Xfce Display Settings dialog

[Mike Freemon]

I suspect the root cause of this is related to a Xfce bug[1], not Qubes,
but since this info is potentially useful to other Qubes users, I
thought I would share.

I found that I was unable to mirror displays (laptop display + external
HDMI monitor) using the Xfce Display Settings dialog box. In my case,
both have a native resolution of 1920x1080, but the Xfce Display
Settings dialog would always reset the resolution of the external
monitor to a lower resolution (1280x1024) and cause truncation of the
screen on the display.

I found that xrandr works fine, so I now have a couple of one-line
scripts to enable/disable mirroring.

To enable mirroring:

xrandr --output eDP1 --mode 1920x1080 --output HDMI2 --mode 1920x1080
--same-as eDP1

To disable:

xrandr --output eDP1 --mode 1920x1080 --output HDMI2 --off

Of course, you'll need to use (xrandr -q) to determine the specific
display names to use in these commands on other laptops.

The tech specs in my case are:

Asus Laptop F556UA-UH71 i7-7500U Intel HD 620
Qubes 3.2
kernel 4.8.12-12
Xfce
xfce4-settings-4.12.0-6.fc23.x86_64

Further details about the hardware is at [2].


[1] https://bugzilla.xfce.org/show_bug.cgi?id=11712
[2]
https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/qubes-users/BUe4tFfERtA/buazJHIzCQAJ