Messages in this thread | | | Date | Wed, 19 May 2010 19:34:04 -0400 | From | Rafi Rubin <> | Subject | Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2) |
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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@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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