On Fri, Mar 19, 2010 at 3:58 AM, Henrik Rydberg [off-list ref] wrote:

Hi Dmitry,

there is an ongoing discussion about adding multitouch to X
(http://lists.x.org/archives/xorg-devel/2010-March/006206.html), which is
beginning to take on more solid form.

One of the suggestions emerging from that discussion is to add the software
finger tracking to the kernel. Back in summer 2009 when I thought about this, I
disregarded it as being too experimental. I have since then reconsidered,
starting to think it really is the right place.

The MT protocol allows applications to take advantage of multi-contact hardware,
but leaves the problems of finger tracking and filtering to the user. Arguably,
no application can make good use of MT without these, so the problem is pushed
forward, in this case to evdev or equivalent.

The knowledge of signal-to-noise ratios and prior input states resides in the
kernel. Because of this, the finger matching and filtering would naturally
reside within the kernel.

So, if there were to appear patches to include matching in the input core, would
you consider them? :-)

I support the idea to add a tracking ID and a filter to _MT_.  I'd
also like to make the filtering method more "device driver developer"
friendly, i.e., give the developer the option to turn the filter on or
off.  If you plan to use a constant for the filtering method, please
allow the developer to choose that constant too.

Another attribute associated with _MT_ is the pressure/capacity.
Report this value would offer more room for MT-aware application to
add new features.

Ping