Play with touchscreen Part II

Tick Chen tick at
Wed Nov 5 06:58:24 CET 2008

Hi Treviño, 
  I played numptyphysics with keyboard few months (May 2008) before and found this
problem. (Getting extra line) I didn't look into this problem, but at that time
I guess it was numptyphysics get the events from SDL when I type
something on keyboard. Therefore, I think this may be a problem of
numptyphysics. I used illume keyboard at that time. 
  You said you found no such issues without mine and Dima's patch. This
may be very interesting. Because the kernel I observe this issues last
time was very old. Maybe there are something different. I will play with
numptyphysics with different kernels again, and to see what's going on.


On Wed, Nov 05, 2008 at 05:44:38AM +0100, "Marco Trevisan (Treviño)" wrote:
> Tick Chen wrote:
> > 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. 
> Recently I've built the stable kernel image, and I've added also your
> touch screen fix, however it - in cooperation with the Dima's soft-tap
> patch - creates some problems.
> I didn't find this issue until I started playing numpty physics with it,
> also if before I got some strange things (like the Qtopia softbar menu
> poping-up while writing a SMS), drawing some lines on numptyphysics
> shows better the issue: practically as soon as I start drawing a line, I
> get two lines, one starting from a random position to the point where I
> started drawing, the other is the one I'm currently writing.
> How to reproduce:
>  - Load numptyphysics (I've tested the 0.2 package in portrait mode)
>  - Draw something
>  - pop-up the illume keyboard and hit a key (i.e. "r" to reset)
>  - Draw another thing
> Now you'll see that your new line will be "double", practically it draws
> both the line from the past focussed point and the one that you're
> currently drawing...
> LATE TEST: after writing this mail I've found that using your
> in the same way, doesn't draw any wrong line.
> So maybe it's just a numptyphysics bug that considers the last touch
> before losing the focus (to hit the keyboard) as the starting point of a
> new move that ends in the point in which you start drawing.
> So is this an application bug, or does it hide something more?
> Thanks...
> PS: Using an older kernel - without the ticks and Dima's patches - I
> can't reproduce this issue at all.
> -- 
> Treviño's World - Life and Linux
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> devel at
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