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input: mt: Document interface updates 

This patch documents the recent input-mt interface changes.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
This commit is contained in:
Henrik Rydberg 2010-12-20 15:09:27 +01:00
parent fcd3027abb
commit 22f075a8d8
1 changed files with 26 additions and 18 deletions
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44
Documentation/input/multi-touch-protocol.txt
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@ -1,6 +1,6 @@
Multi-touch (MT) Protocol
-------------------------
Copyright (C) 2009 Henrik Rydberg <rydberg@euromail.se>
Copyright (C) 2009-2010 Henrik Rydberg <rydberg@euromail.se>
Introduction
@ -169,12 +169,16 @@ described by adding the MINOR parameters, such that MAJOR and MINOR are the
major and minor axis of an ellipse. Finally, the orientation of the oval
shape can be describe with the ORIENTATION parameter.
For type A devices, further specification of the touch shape is possible
via ABS_MT_BLOB_ID.
The ABS_MT_TOOL_TYPE may be used to specify whether the touching tool is a
contact or a pen or something else. Devices with more granular information
may specify general shapes as blobs, i.e., as a sequence of rectangular
shapes grouped together by an ABS_MT_BLOB_ID. Finally, for the few devices
that currently support it, the ABS_MT_TRACKING_ID event may be used to
report contact tracking from hardware [5].
finger or a pen or something else. Finally, the ABS_MT_TRACKING_ID event
may be used to track identified contacts over time [5].
In the type B protocol, ABS_MT_TOOL_TYPE and ABS_MT_TRACKING_ID are
implicitly handled by input core; drivers should instead call
input_mt_report_slot_state().
Event Semantics
@ -247,21 +251,24 @@ ABS_MT_TOOL_TYPE
The type of approaching tool. A lot of kernel drivers cannot distinguish
between different tool types, such as a finger or a pen. In such cases, the
event should be omitted. The protocol currently supports MT_TOOL_FINGER and
MT_TOOL_PEN [2].
MT_TOOL_PEN [2]. For type B devices, this event is handled by input core;
drivers should instead use input_mt_report_slot_state().
ABS_MT_BLOB_ID
The BLOB_ID groups several packets together into one arbitrarily shaped
contact. This is a low-level anonymous grouping for type A devices, and
contact. The sequence of points forms a polygon which defines the shape of
the contact. This is a low-level anonymous grouping for type A devices, and
should not be confused with the high-level trackingID [5]. Most type A
devices do not have blob capability, so drivers can safely omit this event.
ABS_MT_TRACKING_ID
The TRACKING_ID identifies an initiated contact throughout its life cycle
[5]. This event is mandatory for type B devices. The value range of the
TRACKING_ID should be large enough to ensure unique identification of a
contact maintained over an extended period of time.
[5]. The value range of the TRACKING_ID should be large enough to ensure
unique identification of a contact maintained over an extended period of
time. For type B devices, this event is handled by input core; drivers
should instead use input_mt_report_slot_state().
Event Computation
@ -308,18 +315,19 @@ and with ORIENTATION, one can detect twisting of fingers.
Notes
-----
In order to stay compatible with existing applications, the data
reported in a finger packet must not be recognized as single-touch
events. In addition, all finger data must bypass input filtering,
since subsequent events of the same type refer to different fingers.
In order to stay compatible with existing applications, the data reported
in a finger packet must not be recognized as single-touch events.
The first kernel driver to utilize the MT protocol is the bcm5974 driver,
where examples can be found.
For type A devices, all finger data bypasses input filtering, since
subsequent events of the same type refer to different fingers.
For example usage of the type A protocol, see the bcm5974 driver. For
example usage of the type B protocol, see the hid-egalax driver.
[1] With the extension ABS_MT_APPROACH_X and ABS_MT_APPROACH_Y, the
difference between the contact position and the approaching tool position
could be used to derive tilt.
[2] The list can of course be extended.
[3] Multitouch X driver project: http://bitmath.org/code/multitouch/.
[3] The mtdev project: http://bitmath.org/code/mtdev/.
[4] See the section on event computation.
[5] See the section on finger tracking.