Android tablet as a second Ubuntu screen with xrandr and x11vnc

Let's say you have a laptop, an Android tablet and you're working on debugging something.  Wouldn't it be nice to have some extra screen real estate?  The second answer here seemed to be going in the right direction... only one gets stuck moving the mouse into the extended screen area.

So here's a recipe that works (on Ubuntu 14.10 at least). Let's say the actual laptop screen is 1366x768 as in my case; and we want to create another screen of the same resolution:

$ sudo apt-get install x11vnc
$ sudo xrandr --fb 2732x768 --output LVDS1 --panning 2732x768+0+0/2732x768+0+0
$ sleep 3 # wait a moment
$ sudo xrandr --fb 2732x768 --output LVDS1 --panning 1366x768+0+0/2732x768+0+0

Explanation: xrandr (X Resize and Rotate) sets the screen size. To make it think the screen is bigger without doing strange things we first tell it to make a panning setup. With panning the section before the / is the area in which that screen can pan around, after the / is the very important tracking area in which the mouse can move.

Now we can use x11vnc with a clip

sudo x11vnc -clip 1366x768+1367+0 -nocursorshape -nocursorpos

We need to use -nocursorshape and -nocursorpos so the cursor is not dealt with by VNC; the cursor is directly painted on as part of the image.

Now you can take your pick of Android VNC apps and then point it at your laptop's IP address:

The new right half of the screen

Now there's only two and a bit problems left: VNC is not encrypted; so it should run over an SSH tunnel/VPN or something of the like.  Another problem can be lousy WiFi; I'm hoping to kill two bids with one stone by making this run using port forwarding on over the USB cable.

Thanks to this AskUbuntu post.