[Mactel-linux-users] appletouch zig-zags

[Ivan S. <iv...@al...>]

Hello list,
    I have been using the appletouch driver for more than a year now, 
currently on linux 2.6.30. I noticed some time ago when trying to draw 
something on gimp, that when you move your finger the cursor response is 
not linear, but instead kind of "saw-tooth wave" shaped, across both X 
and Y. Of course it is more noticeable if your 'sensitivity' setting on 
X is high, but it is always there. Just to be clear, when you try to 
draw a diagonal line, for example a 45 deg line,  you end up with a 
zig-zag shape, no matter how straight you slide your finger.
    I did not know anything about how the trackpad works until now, and 
I am not completely sure, but the number of 'jumps' of the response 
pattern seems to match the number of sensor elements for both X and Y, 
10x20 in my case (05ac:021b Apple, Inc Internal Keyboard/Trackpad).
    I tried on O$X it seems to work fine. I believe that there is 
something in the algorithm, perhaps in the atp_calculate_abs function, 
that is not totally correct, at least for this trackpad type.
    Any suggestions or comments are welcome.
Regards

--
Iván Stepaniuk
Alba Fotónica S.L.