Play with touchscreen Part II

Tick Chen tick at
Tue Oct 28 16:06:54 CET 2008

Hi List,
  From the first observation of touch screen, we found the up/down event jitter phenomenon. 
If you touch the touchscreen lightly, you will get very unstable data,
and many up/down events in a very short time.
In the driver it already average the data within a threshold. But the
extra up/down events will still makes user space libraries think they get
clicks. This causes annoying problems, and make the GUI hard to use. 

Thanks for Andy's advise and the inspiration from Dima's patch, we found
that can just ignore those extra events with a little bit delay of sending up
envent. If we found it's noise, we can just throw them away. 

I asked many people to play with the touch panel and collected a lot of
logs. I found something. 

1. most jitter event happens in a very shor period of time. most of them
happens less than 0.3 sec
2. Most interval of human double clicks are over 0.1 sec. 0.11~0.2 or
3. Human is not easy to notice things happens in a very short time. For
example "visual staying phenomenon".

I choose 1/16 sec = 0.0625 sec (about the logest duration of vision) as 
the delay threshold. 

And then played with the new driver, it filters out most jitter events.
Although you can still produce noise events on purpose, but it becomes harder.

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