touchscreens in multiscreen setups

Peter Korsgaard jacmet at
Thu Dec 17 23:43:26 PST 2009

>>>>> "Keith" == Keith Packard <keithp at> writes:


 Keith> I'd say tablets and touch screens should report raw device coordinates
 Keith> and let the X server transform them as appropriate. It'd be really cool
 Keith> if we could make all absolute devices report position in floating point
 Keith> using a [0..1] range on each axis. I think. The X server would then
 Keith> transform those as appropriate. I think all that would take is a new
 Keith> PostMotionEvent function that took doubles instead of ints; fixed
 Keith> drivers would use that, broken drivers would continue to report
 Keith> coordinates as they do today.

Does this also include calibration? Some touchscreens apply calibration
parameters in firmware (like nextwindow), so the coordinates you receive
are already calibrated, whereas others provide raw coordinates and we
need to do calibration in software.

It would be nice to have generic calibration support in evdev, instead
of doing this different for each touchscreen. Related to this is
how/where to store calibration parameters. Notice that it sometimes is
needed to recalibrate at runtime (E.G. on resolution change if you don't
have your screen set for scale to fullscreen / don't keep aspect).

Bye, Peter Korsgaard

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