Re: [PATCH] Input: Document the device properties

[Chase Douglas <chase.douglas@canonical.com>]

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