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

[Peter Hutterer <peter.hutterer@who-t.net>]

On Fri, May 21, 2010 at 11:25:41PM +0200, Henrik Rydberg wrote:
> Ping Cheng wrote:
> > On Fri, May 21, 2010 at 8:19 AM, Rafi Rubin <rafi@seas.upenn.edu> wrote:
> [...]
> >> Ping: please confirm, are you actually talking about each finger simultaneously sending multiple positions?
> > 
> > You are definitely on the right track.  The fingers/touch objects can
> > be represented two-dimensionally (x,y) instead of one-dimensionally
> > (ABS_MT_TRACKING_ID).  I think we can survive with the current MT_BLOB
> > definition although some optimization would be helpful, especially for
> > filtering. For the sake of Henrik great effort, I'd like to see his
> > current patchset gets in the tree before we start another round of
> > "suggestions".
> > 
> > Thank you for asking.
> 
> Regarding blobs, I confused myself yesterday. The original intention of the blob
>  id was in fact to be able to "paint" more generic contact forms. However, no
> driver has come close to doing this yet, so it has gotten close to no attention.
> Now, to address the question of how to communicate more elaborate contact forms,
> it seems one can combine the two goals "one position per slot" and "multiple
> positions per contact" by simply repeating the same tracking id for a set of
> slots, like this:
> 
> ABS_SLOT 0
> ABS_MT_TRACKING_ID 14
> ABS_MT_POSITION_X x[0]
> ABS_MT_POSITION_Y y[0]
> ABS_SLOT 1
> ABS_MT_TRACKING_ID 14
> ABS_MT_POSITION_X x[1]
> ABS_MT_POSITION_Y y[1]
> ABS_SLOT 2
> ABS_MT_TRACKING_ID 14
> ABS_MT_POSITION_X x[2]
> ABS_MT_POSITION_Y y[2]
> 
> Not all too different from what you suggested, and there is no blob id involved
> at all. And yes, it would require additional parsing power at the user end.
> Something for later.

This is confusing me now :)

How would a device get multiple x/y coordinates for a single contact? I
could understand a range of coordinates but that's what we have the
ABS_MT_WIDTH_MAJOR/MINOR for. If a touchpoint sends two different x/y
coordinates, wouldn't that be two touchpoints, tracked individually and thus
with a different tracking ID?

I read the example above as _the_ example for using blob IDs to combine
multiple contacts into one semantic contact.

Cheers,
  Peter