Touchscreen troubles

Tias tias at
Mon Dec 14 12:03:25 PST 2009

Petr Štetiar wrote:
> Peter Hutterer <peter.hutterer at> [2009-12-14 10:07:04]:
>> in your case, coordinates aren't strictly rectangular. top right has x of
>> 3633, whereas bottom right has an x of 1693, approximately half of it. the Y
>> coordinate is similar though not quite as extreme.
>> This explains the cutoff, from evdev's POV the x coordinate 2697 (right-hand
>> edge on your diagram) is a bit over half-way into the area (assuming 3633 as
>> max). evdev would map coordinates in the bottom right half to some 'random'
>> coordinates into the top left half.
> Yes, seems so.
>> evdev doesn't have any facilities yet to cope with the scaling needed for
>> this device. You'd have to start implementing your own mapping system and
>> plug it into evdev. sorry.
> Ok, I'll try :) Thanks.

You can take a look at the tslib driver. It's a bit hard to find 
information on, but as far as I know, it's originally created for 
embedded devices and you need to use a framebuffer for video.
It's calibration module can handle linear scaling of touchscreens, as 
well as rotation.
It might do calibration as described in
If not, you could take a closer look at the technique described there 
too ; )

Hope it helps you a bit further,

Kind regards,

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