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

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Date:	Wed, 19 May 2010 19:34:04 -0400
From:	Rafi Rubin <rafi@...s.upenn.edu>
To:	Ping Cheng <pinglinux@...il.com>
CC:	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>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	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)

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).


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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