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Virtual screen

Ever wondered if you could drag a window from your PC to a phone or tablet standing on your desk? It turns out you can!

I wrote this guide, because I've only found bits and pieces around, with many things being outdated or not working.

How to

1) Create a virtual screen

Install evdi kernel module

evdi

git clone https://github.com/DisplayLink/evdi.git
cd evdi/module

make && sudo make install
# or
sudo make install_dkms

Add "evdi" to /etc/modules-load.d/local.conf.

Add "options evdi initial_device_count=1" to /etc/modprobe.d/local.conf.

WARNING! This next step will freeze your Xorg, so you might want to reboot instead or be clever about killing your Xorg or something.

sudo modprobe evdi

2) Set a resolution and position to your virtual screen

w=1280
h=720

set -- $(cvt "$w" "$h" 60 | grep Modeline)
name="${2#\"}"
name="${name%\"}"
shift 2

xrandr --newmode "$name" "$@"
xrandr --addmode DVI-I-1-1 "$name"
xrandr \
    --output DVI-I-1-1 \
    --mode "$name" \
    --left-of eDP-1

3) Share your virtual screen with VNC

geometry="$(xrandr | grep DVI-I-1-1 | cut -d" " -f 3)"
x0vncserver \
    -display :0 \
    -SecurityTypes none \
    -Geometry "$geometry"
# or
x11vnc \
    -display :0 \
    -clip "$geometry" \
    -forever

For x0vncserver instead of "-SecurityTypes none" you might want to use "-PasswordFile" option instead. Consult your man page.

4) (optional) Attach Android device through USB cable

adb reverse tcp:5900 tcp:5900

Now you can point your VNC client application (like MultiVNC) to "localhost:5900".

MultiVNC

What is wrong in other guides

Using obsolete "intel" driver

Intel driver has 'Option "VirtualHeads"', but you really want to stick to default "modesetting" driver.

Using "dummy" driver

According to ArchLinux wiki page "Extreme Multihead"

Extreme Multihead

It is in principle possible to set up a dummy device alongside a real device by adding a dummy device and xinerama configuration to xorg. It is tricky to have this configuration working properly, and it is not ideal for laptops, as you won't be able to hotplug monitors.

Using "xrandr --fb" to enlarge screen size

You can't make a window go fullscreen or snap to the edges.

Using an unused output

It fails for me. I have a DP-1 in xrandr, but no physical DisplayPort output.

$ xrandr --output DP-1 \
    --mode 1280x720_60.00 \
    --left-of eDP-1
xrandr: Configure crtc 2 failed

References

https://askubuntu.com/questions/28608/how-do-you-use-an-android-tablet-as-a-second-display

https://unix.stackexchange.com/questions/585069/unable-to-add-a-virtual-dispplay-to-xorg/585078#585078

https://github.com/brunodles/linux-second-screen/blob/master/tutorial.md

https://wiki.archlinux.org/index.php/Extreme_Multihead

Date: 2021-01-09