linux-kernel - Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

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Date:	Thu, 20 May 2010 10:21:05 +1000
From:	Peter Hutterer <peter.hutterer@...-t.net>
To:	Rafi Rubin <rafi@...s.upenn.edu>
Cc:	Ping Cheng <pinglinux@...il.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Stephane Chatty <chatty@...c.fr>,
	Michael Poole <mdpoole@...ilus.org>
Subject: Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

On Wed, May 19, 2010 at 07:34:04PM -0400, Rafi Rubin wrote:
> My understanding is that it would be more like
> +   SYN_MT_SLOT 0
> +   ABS_MT_POSITION_X x
> +   ABS_MT_POSITION_Y y
> +   SYN_REPORT
> +   SYN_MT_SLOT 0
> +   ABS_MT_POSITION_X x
> +   ABS_MT_POSITION_Y y
> +   SYN_REPORT
> +   SYN_MT_SLOT 0
> +   ABS_MT_POSITION_X x
> +   ABS_MT_POSITION_Y y
> +   SYN_MT_SLOT 1
> +   ABS_MT_POSITION_X x
> +   ABS_MT_POSITION_Y y
> +   SYN_REPORT
> 
> 
> (2 events from 1 finger, followed by 1 event with both).

where does the ABS_MT_BLOB_ID come in then? I thought this was the use-case
it was added for. With the example above, you're updating the position for
the finger three times, not specifying that there are 3 _simultaneous_ but
disparate touches of the same finger.

I'm thinking of a palm touch which may (for some hand shapes) gives you two
blobs right next to each other but separated by a thin line.
So palm + finger gives you three blobs in three slots, two of them linked by
contact ID?

Cheers,
  Peter

> On 05/19/2010 06:43 PM, Ping Cheng wrote:
> >Hi Henrik,
> >
> >I am trying to link the protocol to the actual multi-touch devices in
> >my "mind". Hope it helps you to point out the mismatch between my
> >imagination and the protocol.  Please see details in line.
> >
> >Ping
> >
> >On Tue, May 18, 2010 at 1:10 PM, Henrik Rydberg<rydberg@...omail.se>  wrote:
> >>This patch adds documentation for the SYN_MT_SLOT event and
> >>gives examples of how to use the event slot protocol.
> >
> >Am I right in thinking that SYN_MT_SLOT represents to the actual touch
> >area/finger on the surface? There could be more than one (x,y) (a few
> >points that form an irregular shape) that represents one finger.  The
> >following example shows that slot 0 (finger 1) touched three points on
> >the surface while slot 1 (finger 2) only has one point reported:
> >
> >+   SYN_MT_SLOT 0
> >+   ABS_MT_TRACKING_ID 45
> >+   ABS_MT_POSITION_X x[0]
> >+   ABS_MT_POSITION_Y y[0]
> >+   ABS_MT_TRACKING_ID 46
> >+   ABS_MT_POSITION_X x[1]
> >+   ABS_MT_POSITION_Y y[1]
> >+   ABS_MT_TRACKING_ID 47
> >+   ABS_MT_POSITION_X x[2]
> >+   ABS_MT_POSITION_Y y[2]
> >+   SYN_MT_SLOT 1
> >+   ABS_MT_TRACKING_ID 30
> >+   ABS_MT_POSITION_X x[3]
> >+   ABS_MT_POSITION_Y y[3]
> >+   SYN_REPORT
> >
> >If my assumption is correct, i.e., one slot can have more than one
> >point, I would think ABS_MT_TRACKING_ID may not have to be a required
> >entry inside SYN_MT_SLOT.  To the user land clients/drivers,
> >SYN_MT_SLOT itself could serve as an ID. So, the following case is
> >also a type B ( we know there are two touch areas. But we don't keep
> >track of the points inside the areas):
> >
> >+   SYN_MT_SLOT 0
> >+   ABS_MT_POSITION_X x[0]
> >+   ABS_MT_POSITION_Y y[0]
> >+   ABS_MT_POSITION_X x[1]
> >+   ABS_MT_POSITION_Y y[1]
> >+   ABS_MT_POSITION_X x[2]
> >+   ABS_MT_POSITION_Y y[2]
> >+   SYN_MT_SLOT 1
> >+   ABS_MT_POSITION_X x[3]
> >+   ABS_MT_POSITION_Y y[3]
> >+   SYN_REPORT
> >
> >So, an EVIO for X driver to retrieve the number of SLOTs would be very
> >helpful.  Something like the following would do the work:
> >
> >input_set_abs_params(input_dev, ABS_MT_SLOT, 0, 12, 0, 0);
> >
> >which tells the user land clients that they can expect up to 13 touch areas.
> >
> >>+The main difference between the raw type A protocol and the higher level
> >>+type B slot protocol lies in the usage of identifiable contacts. The slot
> >>+protocol requires the use of the ABS_MT_TRACKING_ID,
> >
> >With what I said above, I think ABS_MT_TRACKING_ID is not the unique
> >identifier for type B protocol. It is the fact that we can identify
> >individual touch areas and use ABS_MT_SLOT to report them that makes
> >it a type B event.
> >
> >>ABS_MT_TRACKING_ID, either provided by the
> >>+hardware of computed from the raw data [5].
> >                    ^^ or  (is it?)
> >
> >I agree with this ABS_MT_TRACKING_ID definition.  I would think something like:
> >
> >input_set_abs_params(input_dev, ABS_MT_TRACKING_ID, 0, 47, 0, 0);
> >
> >which tells the clients that total of 48 points are tracked, would be helpful.
> >
> >Another topic that may be irrelevant to this patch is the filter. With
> >the use of ABS_MT_TRACKING_ID, a filter can be applied to discard the
> >useless repeated points or less than a certain number of points
> >movement.
> >
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