linux-kernel - Re: [PATCH] input: mt: Add an envelope tool type

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Message-ID: <20101208235805.GE15294@core.coreip.homeip.net>
Date:	Wed, 8 Dec 2010 15:58:06 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ping Cheng <pinglinux@...il.com>
Cc:	Chase Douglas <chase.douglas@...onical.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] input: mt: Add an envelope tool type

On Wed, Dec 08, 2010 at 03:43:51PM -0800, Ping Cheng wrote:
> On Wed, Dec 8, 2010 at 9:43 AM, Chase Douglas
> <chase.douglas@...onical.com> wrote:
> > On 12/07/2010 03:29 AM, Henrik Rydberg wrote:
> >> Some touch devices are capable of detecting the envelope or hull
> >> of the touches, but not the touches themselves. This patch adds
> >> the MT_TOOL_ENVELOPE touch type to be used for such devices.
> >>
> >> Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
> >> ---
> >> Hi all,
> >>
> >> This patch represents an MT solution for those devices that can detect
> >> and report some effects of dual touch, but cannot report individual
> >> contacts. Synaptics and elantech are two examples. Having the drivers
> >> report the bounding rectangle of the touches is useful in userland,
> >> since the information makes it possible to implement zooming
> >> gestures. At the same time, it would be confusing to send these
> >> envelope points as fingers, since they clearly are not. As a remedy,
> >> introduce MT_TOOL_ENVELOPE, which tells applications that care about
> >> details that these are not real fingers, at the same time as it allows
> >> gesture applications based on MT data to function without
> >> modification.
> >
> > Is it assumed that the envelop has only two touches comprising it? Or is
> > it any number of touches? If it's any number of touches, how does one
> > know how many touches it is?
> 
> Those are good questions. Specifying how many touches are in the
> envelop makes sense. It also covers rectangle as a special case of
> envelop.

I have a feeling that trying to accomodate non-rectangular, more than 2
point shapes without using native MT data is over-engineering the
problem... Do we have examples other than older generation Elantechs and
Synaptics that need envelope notion?

-- 
Dmitry
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