If you read about calibrating touchscreen with X11 and are capable of simple addition and division, you won't have a problem building the transformation matrix and applying it. I won't cover the same details on how to set the matrix using
xinput set-prop since I just want to write down the resulting matrix and, perhaps, save people some time if they have a setup similar to mine.
To get the name of the device, open Terminal and punch in:
In the output I found that my "Acer T232HL"'s input component is actually called "Advanced Silicon S.A CoolTouch(TM) System". I can see all of its properties with:
xinput list-props Advanced Silicon S.A CoolTouch(TM) System
Since I've set up the screen to be on the left site, that means top-left corner of my touch area is simply offset by 0,0, and bottom-right is 1920,1080. Considering that the total width of the usable X area is 1920+1280, I get 1920/3600=0.6 as the c0 constant on the above link.
My usable area's height is max(1080, 800) (the respective y component of the resolutions of the two displays). Considering that touch area's height is also 1080, then the c2 component does not need to be scaled and should be exactly 1.
I also have absolutely no offsets, so c1 and c3 stay 0.
xinput set-prop "Advanced Silicon S.A CoolTouch(TM) System" --type=float "Coordinate Transformation Matrix" 0.6 0 0 0 1 0 0 0 1
# And if needed, to make the display configured as described above:
xrandr --output DP-0 --auto --left-of LVDS-0
From the times when I was trying to get Linux to run on iPaq H3800 devices using the kernel and distributions published at the now-defunct handhelds.org, I remember the "tslib" which included a touchscreen calibration tool. I wonder if that can and should be used to calibrate the modern multitouch displays.
Update (April 5th 2014): I just dug out package 'xinput_calibrator' by random googling, but have not tried it out yet.