Raw mouse input is distorted

Hauberg hauberg at gmail.com
Wed Sep 17 06:46:17 PDT 2008

Hi All,
  First post here, so if I'm asking the wrong place, please let me know...
Anyway, at work I have a DMC touchscreen that Linux recognizes with the
'usbtouchscreen' kernel module. If I want to use this touchscreen with X I
have to calibrate the screen, and give some parameters to the 'evtouch'
driver. This is working just fine except the calibration procedure requires
that I restart X. Since I want to give our customers a chance to calibrate
the screen, I'm not too fond of this X-restarting (it makes our product look
hacky) .
  So, in order to solve this problem, I've extended the 'usbtouchscreen'
kernel module such that it can read the calibration parameters, and
transform the coordinates accordingly (if anybody wants the patch for
'usbtouchscreen' let me know). With this change, I can see (via kernel logs)
that the output generated by the 'usbtouchscreen' module corresponds quite
well to the physical position where I touch the screen. So far so good...
  Now, my problem is that X seems to somehow accelerate the output from the
'usbtouchscreen' module, so that when I move my finger to the left, the
cursor moves about twice as far to the left as my finger did. This does not
correspond to the output from the 'usbtouchscreen' module. So, I'm a bit
confused here: does X place the cursor at the position outputted by the
kernel, or does it do some fancy things?


P.S. I guess I should mention that I'm using OpenSUSE 11.0.

P.P.S. It might be relevant to say that output is sent from 'usbtouchscreen'
using 'input_report_abs' which calls 'input_event' with the 'EV_ABS' flag.
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