Date: Mon, 20 Dec 2010 18:17:34 +1000
From: Peter Hutterer <peter.hutterer@who-t.net>
To: Henrik Rydberg <rydberg@euromail.se>
Cc: Chase Douglas <chase.douglas@canonical.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Jiri Kosina <jkosina@suse.cz>, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] input: mt: Interface and MT_TOOL documentation updates
Message-ID: <20101220081734.GB17764@barra.redhat.com>
References: <1292001842-5000-1-git-send-email-rydberg@euromail.se>
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[sorry, got stuck in my outbox for some reason]

On Tue, Dec 14, 2010 at 10:10:10AM +0100, Henrik Rydberg wrote:
> On 12/14/2010 05:36 AM, Peter Hutterer wrote:
> 
> > On Tue, Dec 14, 2010 at 12:25:26AM +0100, Henrik Rydberg wrote:
> >>>> The envelope contacts serve as a way to detect a small area of fingers or a
> >>
> >>>> large area of fingers. There is nothing inherently problematic with having one
> >>>> or three or more such contacts.
> >>>
> >>> Then I'm more confused :).
> >>>
> >>> I see one problem: devices that report two touch points, (X1, Y1) and
> >>> (X2, Y2), but in reality the touches could be at (X1, Y2) and (X2, Y1)
> >>> instead. Using a rectangle helps resolve this issue for panning and
> >>> pinching, though not for rotation.
> >>
> >>
> >> If panning and pinching and rotation could all be recovered properly, then the
> >> individual contacts could actually have been reconstructed properly in the first
> >> place. This is the whole point - there is not enough information available for
> >> rotation to be recovered properly.
> > 
> > can you post an example event stream of the MT_ENVELOPE tool? I'm having
> > trouble wrapping my head around it.
> 
> 
> Here is an example for you: You sit in a car. You turn your steering wheel left
> or right to follow the road. Now, imagine that 40% of the time, when you turn
> left, the car actually turns right. This is the behavior you get from the raw
> data. Now, instead soak your gloves in soap. At least now you know that your car
> will go straight 100% of the time. The MT_ENVELOPE tool is the soapy glove.
> That's all there is to it.
> 
> The synaptics driver patch sent recently contains an example event stream
> generator, in case you want to dwell on more details.
> 
> Personally, I am done bending myself backwards to support "old" or "semi-mt"
> hardware I never use myself. If somebody cares deeply enough, send a patch. Or
> forever hold your peace.

thanks, I understood the concept but I was trying to get the actual event
stream out of this patch set. I missed the synaptics one, makes sense now.

Cheers,
  Peter
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