using SYNAPTICs touchpad as primitive graphics tablet

Peter Hutterer peter.hutterer at
Thu Jul 15 16:20:12 PDT 2010

On Thu, Jul 15, 2010 at 01:42:02PM +1000, Peter Rayner wrote:
> Let me give 3 sentences of background to my request.
> I am a totally blind researcher who needs to look at 2-dimensional
> data.  As a hobby project I'm trying to write an application to use
> graphics tablets and audio output to do this. I would like to extend
> this to built-in touchpads on laptops but I have to get the absolute
> position of a finger on the touchpad rather than just relative
> movement.

the synaptics driver doesn't do this, but the evdev driver does. So you need
to configure your X server to use the evdev driver for the touchpad instead.
The following configuration snippet will do that for you provided you're
running server 1.8 or later.

Section "InputClass"
        Identifier "evdev touchpad"
        MatchIsTouchpad "on"
        Driver "evdev"
        Option "Mode" "absolute"

Save this as /etc/X11/xorg.conf.d/99-evdev-touchpad.conf and restart the
server. Note that this only changes the behaviour of the touchpad itself,
not the data in the events but then again that data is always absolute
Also, by using evdev instead of synaptics you're losing the ability for
two-finger scrolling, tapping, etc. Is this a problem in your case?


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