linux-kernel - Re: [PATCH] Input: Document the device properties

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Message-ID: <4F26CDF3.5080606@canonical.com>
Date:	Mon, 30 Jan 2012 18:05:55 +0100
From:	Chase Douglas <chase.douglas@...onical.com>
To:	Jussi Pakkanen <jussi.pakkanen@...onical.com>
CC:	Henrik Rydberg <rydberg@...omail.se>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: Document the device properties

On 01/30/2012 01:23 PM, Jussi Pakkanen wrote:
> On 01/30/2012 10:35 AM, Henrik Rydberg wrote:
>> +INPUT_PROP_SEMI_MT:
>> +------------------
>> +Some touchpads, most common between 2008 and 2011, can detect the presence
>> +of multiple contacts without resolving the individual positions; only the
>> +number of contacts and the corresponding bounding box is known. For such
>> +touchpads, the semi-mt property should be set.
> 
> A "corresponding bounding box" usually means "a bounding box that 
> contains all touches on the touchpad". I've been told (though I have not 
> checked it myself) that there are devices that don't do this. They only 
> report a bounding box for some subset of touches. If this is the case, 
> it should be documented here.

Yeah, I thought Henrik's definition was correct for a long time, but
when Derek Foreman (I think) proposed some patches for the latest
synaptics devices I took a closer look at my semi-mt synaptics trackpad.
The coordinates it gave were locations based on two of the touches. When
three touches are on the touchpad, it gave a bounding box of two of the
touches, and there's no way to tell which two.

-- Chase

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