By default, X will scale the touchscreen's input to the display, this typically results in off screen areas will be included, resulting in touch sensing to be
To remove off screen areas, evdev calibration must be used. When calibration is used, touchscreen co-ordinates outside of the calibrated area will act as if they're off screen. moving a finger from inside the area to outside the area will result in a release event at the edge of the screen. Moving from outside to inside will result in a press. The intent is that the screen behave as if the calibrated area was its physical boundary.
Setting this up for the eGalax touch screen on SABRE Lite can be done by
creating a file in
/usr/share/X11/xorg.conf.d with the contents:
Section "InputClass" Identifier "Calibrated Touch Screen" MatchProduct "eGalax Touch Screen" Driver "evdev" Option "Calibration" "0 16384 0 32768" EndSection
or, for the Iiyama touch screen on the intel reference platform:
Section "InputClass" Identifier "Calibrated Touch Screen" MatchProduct "QUANTA OpticalTouchScreen" Driver "evdev" Option "Calibration" "0 1000 0 1080" EndSection
The calibration numbers are low X, high X, low Y, high Y in unscaled touch sensor co-ordinates. X will scale touch sensor motion inside this range to fill the display.
This can also be done at run-time without changing configuration files by doing
the following (xinput may need to be installed with
apt-get install xinput):
xinput "eGalax Touch Screen" "Evdev Axis Calibration" 0 16384 0 32768
If using different devices, use
to find the name.