Re: [iPAQ] iPAQ touchscreen jitters

The issue is that such filtering is often/usually hardware specific,
and having to have this on a per hardware basis in all apps is a
multiplicative explosion of hardware devices/appications that talk to
the touchscreen driver.

So pushing it to user space just makes the pain N times worse....
Drivers also need to provide a certain amount of device abstraction
to be useful.

Clearly, if the filtering algorithms become crazy, we'd have to go
to some GPM kind of solution, but hopefully, we aren't in that
level of mess for most hardware out there. We hope/expect that
the 36xx touch screen is not so insane.

We'd like to avoid the mouse mess we have already: ergo the previously
alluded to design discussions with Linus and Pavel Keith and I need
to write up (with concrete proposal of a new interface).

                                - Jim

> Sender: ipaq-admin@handhelds.org
> From: David Woodhouse <dwmw2@infradead.org>
> Date: Thu, 03 Jan 2002 16:18:20 +0000
> To: "Christian, Andrew" <Andrew.Christian@compaq.com>
> Cc: "Disconnect" <dis@sigkill.net>, ipaq@handhelds.org
> Subject: Re: [iPAQ] iPAQ touchscreen jitters
> -----
> Andrew.Christian@compaq.com said:
> > I've updated the iPAQ touchscreen driver to include an anti-jitter
> > filter (thanks! to Disconnect for the loan of an iPAQ with a dicey
> > touchscreen). The latest h3600_ts driver now adds the
> > "jitter_threshold", which specifies how many pixels the stylus must
> > move before the touchscreen will report a mouse-moved event. The
> > default value is "1" (so moves of only a single pixel are ignored)
> > which eliminates a fair amount of jitter.
>
> Wouldn't this kind of filtering be better in userspace?
>

--
Jim Gettys
Cambridge Research Laboratory
Compaq Computer Corporation
jg@pa.dec.com