linux-kernel - Re: input: mt: Software finger tracking in the kernel?

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Message-ID: <167e8a331003192151o593809bbhcda68e284185dd4a@mail.gmail.com>
Date:	Fri, 19 Mar 2010 21:51:22 -0700
From:	Ping Cheng <pinglinux@...il.com>
To:	Henrik Rydberg <rydberg@...esh.se>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: input: mt: Software finger tracking in the kernel?

On Fri, Mar 19, 2010 at 3:58 AM, Henrik Rydberg <rydberg@...esh.se> 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
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