Running Ubuntu Touch

Display settings

When the device boots, you’ll probably notice that everything is very small. There are two variables that set the content scaling for Unity 8 and Ubuntu Touch applications: GRID_UNIT_PX and QTWEBKIT_DPR.

There are also some other options available that may be useful for you depending on your device’s form factor. These are discussed below.

All of these settings are guessed by Unity 8 if none are set. There are many cases, however, where the guess is wrong (for example, very high resolution phone displays will be identified as desktop computers). To manually set a value for these variables, simply create a file at /etc/ubuntu-session.d/[codename].conf specifying them. For example, this is the file for the Nexus 7 tablet:

$ cat /etc/ubuntu-touch-session.d/flo.conf
GRID_UNIT_PX=18
QTWEBKIT_DPR=2.0
NATIVE_ORIENTATION=landscape
FORM_FACTOR=tablet

Methods for deriving values for these variables are below.

Display scaling

GRID_UNIT_PX (Pixels per Grid Unit or Px/GU) is specific to each device. Its goal is to make the user interface of the system and its applications the same perceived size regardless of the device they are displayed on. It is primarily dependent on the pixel density of the device’s screen and the distance to the screen the user is at. The latter value cannot be automatically detected and is based on heuristics. We assume that tablets and laptops are the same distance and that they are held at 1.235 times the distance phones tend to be held at.

QTWEBKIT_DPR sets the display scaling for the Oxide web engine, so changes to this value will affect the scale of the browser and webapps.

A reference device has been chosen from which we derive the values for all other devices. The reference device is a laptop with a 120ppi screen. However, there is no exact formula since these options are set for perceived size rather than physical size . Here are some values for other devices so you may derive the correct one for yours:

Device Resolution Display Size PPI Px/GU QtWebKit DPR
‘Normal’ density laptop N/A N/A 96-150 8 1.0
ASUS Nexus 7 1280x800 7” 216 12 2.0
‘High’ density laptop N/A N/A 150-250 16 1.5
Samsung Galaxy Nexus 1280x720 4.65” 316 18 2.0
LG Nexus 4 1280x768 4.7” 320 18 2.0
Samsung Nexus 10 2560x1600 10.1” 299 20 2.0
Fairphone 2 1080x1920 5” 440 23 2.5
LG Nexus 5 1080x1920 4.95” 445 23 2.5

Experiment with a few values to find one that feels good when compared to the Ubuntu Touch experience on other devices. If you are unsure of which is the best, share some pictures (including some object for scale) along with the device specs with us.

Form factor

There are two other settings that may be of interest to you.

FORM_FACTOR specifies the device’s form factor. This value is set as the device’s Chassis, which you can find by running hostnamectl. The acceptable values are handset, tablet, laptop and desktop. Apps such as the gallery use this information to change their functionality. For more information on the Chassis, see the freedesktop.org hostnamed specification.

NATIVE_ORIENTATION sets the display orientation for the device’s built-in screen. This value is used whenever autorotation isn’t working correctly or when an app wishes to be locked to the device’s native orientation. Acceptable values are landscape, which is normally used for tablets, laptops, and desktops; and portrait, which is usually used for phone handsets.