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    SubjectRe: [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@euromail.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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