mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-06 01:16:42 +07:00
22f075a8d8
This patch documents the recent input-mt interface changes. Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
334 lines
13 KiB
Plaintext
334 lines
13 KiB
Plaintext
Multi-touch (MT) Protocol
|
|
-------------------------
|
|
Copyright (C) 2009-2010 Henrik Rydberg <rydberg@euromail.se>
|
|
|
|
|
|
Introduction
|
|
------------
|
|
|
|
In order to utilize the full power of the new multi-touch and multi-user
|
|
devices, a way to report detailed data from multiple contacts, i.e.,
|
|
objects in direct contact with the device surface, is needed. This
|
|
document describes the multi-touch (MT) protocol which allows kernel
|
|
drivers to report details for an arbitrary number of contacts.
|
|
|
|
The protocol is divided into two types, depending on the capabilities of the
|
|
hardware. For devices handling anonymous contacts (type A), the protocol
|
|
describes how to send the raw data for all contacts to the receiver. For
|
|
devices capable of tracking identifiable contacts (type B), the protocol
|
|
describes how to send updates for individual contacts via event slots.
|
|
|
|
|
|
Protocol Usage
|
|
--------------
|
|
|
|
Contact details are sent sequentially as separate packets of ABS_MT
|
|
events. Only the ABS_MT events are recognized as part of a contact
|
|
packet. Since these events are ignored by current single-touch (ST)
|
|
applications, the MT protocol can be implemented on top of the ST protocol
|
|
in an existing driver.
|
|
|
|
Drivers for type A devices separate contact packets by calling
|
|
input_mt_sync() at the end of each packet. This generates a SYN_MT_REPORT
|
|
event, which instructs the receiver to accept the data for the current
|
|
contact and prepare to receive another.
|
|
|
|
Drivers for type B devices separate contact packets by calling
|
|
input_mt_slot(), with a slot as argument, at the beginning of each packet.
|
|
This generates an ABS_MT_SLOT event, which instructs the receiver to
|
|
prepare for updates of the given slot.
|
|
|
|
All drivers mark the end of a multi-touch transfer by calling the usual
|
|
input_sync() function. This instructs the receiver to act upon events
|
|
accumulated since last EV_SYN/SYN_REPORT and prepare to receive a new set
|
|
of events/packets.
|
|
|
|
The main difference between the stateless type A protocol and the stateful
|
|
type B slot protocol lies in the usage of identifiable contacts to reduce
|
|
the amount of data sent to userspace. The slot protocol requires the use of
|
|
the ABS_MT_TRACKING_ID, either provided by the hardware or computed from
|
|
the raw data [5].
|
|
|
|
For type A devices, the kernel driver should generate an arbitrary
|
|
enumeration of the full set of anonymous contacts currently on the
|
|
surface. The order in which the packets appear in the event stream is not
|
|
important. Event filtering and finger tracking is left to user space [3].
|
|
|
|
For type B devices, the kernel driver should associate a slot with each
|
|
identified contact, and use that slot to propagate changes for the contact.
|
|
Creation, replacement and destruction of contacts is achieved by modifying
|
|
the ABS_MT_TRACKING_ID of the associated slot. A non-negative tracking id
|
|
is interpreted as a contact, and the value -1 denotes an unused slot. A
|
|
tracking id not previously present is considered new, and a tracking id no
|
|
longer present is considered removed. Since only changes are propagated,
|
|
the full state of each initiated contact has to reside in the receiving
|
|
end. Upon receiving an MT event, one simply updates the appropriate
|
|
attribute of the current slot.
|
|
|
|
|
|
Protocol Example A
|
|
------------------
|
|
|
|
Here is what a minimal event sequence for a two-contact touch would look
|
|
like for a type A device:
|
|
|
|
ABS_MT_POSITION_X x[0]
|
|
ABS_MT_POSITION_Y y[0]
|
|
SYN_MT_REPORT
|
|
ABS_MT_POSITION_X x[1]
|
|
ABS_MT_POSITION_Y y[1]
|
|
SYN_MT_REPORT
|
|
SYN_REPORT
|
|
|
|
The sequence after moving one of the contacts looks exactly the same; the
|
|
raw data for all present contacts are sent between every synchronization
|
|
with SYN_REPORT.
|
|
|
|
Here is the sequence after lifting the first contact:
|
|
|
|
ABS_MT_POSITION_X x[1]
|
|
ABS_MT_POSITION_Y y[1]
|
|
SYN_MT_REPORT
|
|
SYN_REPORT
|
|
|
|
And here is the sequence after lifting the second contact:
|
|
|
|
SYN_MT_REPORT
|
|
SYN_REPORT
|
|
|
|
If the driver reports one of BTN_TOUCH or ABS_PRESSURE in addition to the
|
|
ABS_MT events, the last SYN_MT_REPORT event may be omitted. Otherwise, the
|
|
last SYN_REPORT will be dropped by the input core, resulting in no
|
|
zero-contact event reaching userland.
|
|
|
|
|
|
Protocol Example B
|
|
------------------
|
|
|
|
Here is what a minimal event sequence for a two-contact touch would look
|
|
like for a type B device:
|
|
|
|
ABS_MT_SLOT 0
|
|
ABS_MT_TRACKING_ID 45
|
|
ABS_MT_POSITION_X x[0]
|
|
ABS_MT_POSITION_Y y[0]
|
|
ABS_MT_SLOT 1
|
|
ABS_MT_TRACKING_ID 46
|
|
ABS_MT_POSITION_X x[1]
|
|
ABS_MT_POSITION_Y y[1]
|
|
SYN_REPORT
|
|
|
|
Here is the sequence after moving contact 45 in the x direction:
|
|
|
|
ABS_MT_SLOT 0
|
|
ABS_MT_POSITION_X x[0]
|
|
SYN_REPORT
|
|
|
|
Here is the sequence after lifting the contact in slot 0:
|
|
|
|
ABS_MT_TRACKING_ID -1
|
|
SYN_REPORT
|
|
|
|
The slot being modified is already 0, so the ABS_MT_SLOT is omitted. The
|
|
message removes the association of slot 0 with contact 45, thereby
|
|
destroying contact 45 and freeing slot 0 to be reused for another contact.
|
|
|
|
Finally, here is the sequence after lifting the second contact:
|
|
|
|
ABS_MT_SLOT 1
|
|
ABS_MT_TRACKING_ID -1
|
|
SYN_REPORT
|
|
|
|
|
|
Event Usage
|
|
-----------
|
|
|
|
A set of ABS_MT events with the desired properties is defined. The events
|
|
are divided into categories, to allow for partial implementation. The
|
|
minimum set consists of ABS_MT_POSITION_X and ABS_MT_POSITION_Y, which
|
|
allows for multiple contacts to be tracked. If the device supports it, the
|
|
ABS_MT_TOUCH_MAJOR and ABS_MT_WIDTH_MAJOR may be used to provide the size
|
|
of the contact area and approaching contact, respectively.
|
|
|
|
The TOUCH and WIDTH parameters have a geometrical interpretation; imagine
|
|
looking through a window at someone gently holding a finger against the
|
|
glass. You will see two regions, one inner region consisting of the part
|
|
of the finger actually touching the glass, and one outer region formed by
|
|
the perimeter of the finger. The diameter of the inner region is the
|
|
ABS_MT_TOUCH_MAJOR, the diameter of the outer region is
|
|
ABS_MT_WIDTH_MAJOR. Now imagine the person pressing the finger harder
|
|
against the glass. The inner region will increase, and in general, the
|
|
ratio ABS_MT_TOUCH_MAJOR / ABS_MT_WIDTH_MAJOR, which is always smaller than
|
|
unity, is related to the contact pressure. For pressure-based devices,
|
|
ABS_MT_PRESSURE may be used to provide the pressure on the contact area
|
|
instead. Devices capable of contact hovering can use ABS_MT_DISTANCE to
|
|
indicate the distance between the contact and the surface.
|
|
|
|
In addition to the MAJOR parameters, the oval shape of the contact can be
|
|
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
|
|
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
|
|
---------------
|
|
|
|
ABS_MT_TOUCH_MAJOR
|
|
|
|
The length of the major axis of the contact. The length should be given in
|
|
surface units. If the surface has an X times Y resolution, the largest
|
|
possible value of ABS_MT_TOUCH_MAJOR is sqrt(X^2 + Y^2), the diagonal [4].
|
|
|
|
ABS_MT_TOUCH_MINOR
|
|
|
|
The length, in surface units, of the minor axis of the contact. If the
|
|
contact is circular, this event can be omitted [4].
|
|
|
|
ABS_MT_WIDTH_MAJOR
|
|
|
|
The length, in surface units, of the major axis of the approaching
|
|
tool. This should be understood as the size of the tool itself. The
|
|
orientation of the contact and the approaching tool are assumed to be the
|
|
same [4].
|
|
|
|
ABS_MT_WIDTH_MINOR
|
|
|
|
The length, in surface units, of the minor axis of the approaching
|
|
tool. Omit if circular [4].
|
|
|
|
The above four values can be used to derive additional information about
|
|
the contact. The ratio ABS_MT_TOUCH_MAJOR / ABS_MT_WIDTH_MAJOR approximates
|
|
the notion of pressure. The fingers of the hand and the palm all have
|
|
different characteristic widths [1].
|
|
|
|
ABS_MT_PRESSURE
|
|
|
|
The pressure, in arbitrary units, on the contact area. May be used instead
|
|
of TOUCH and WIDTH for pressure-based devices or any device with a spatial
|
|
signal intensity distribution.
|
|
|
|
ABS_MT_DISTANCE
|
|
|
|
The distance, in surface units, between the contact and the surface. Zero
|
|
distance means the contact is touching the surface. A positive number means
|
|
the contact is hovering above the surface.
|
|
|
|
ABS_MT_ORIENTATION
|
|
|
|
The orientation of the ellipse. The value should describe a signed quarter
|
|
of a revolution clockwise around the touch center. The signed value range
|
|
is arbitrary, but zero should be returned for a finger aligned along the Y
|
|
axis of the surface, a negative value when finger is turned to the left, and
|
|
a positive value when finger turned to the right. When completely aligned with
|
|
the X axis, the range max should be returned. Orientation can be omitted
|
|
if the touching object is circular, or if the information is not available
|
|
in the kernel driver. Partial orientation support is possible if the device
|
|
can distinguish between the two axis, but not (uniquely) any values in
|
|
between. In such cases, the range of ABS_MT_ORIENTATION should be [0, 1]
|
|
[4].
|
|
|
|
ABS_MT_POSITION_X
|
|
|
|
The surface X coordinate of the center of the touching ellipse.
|
|
|
|
ABS_MT_POSITION_Y
|
|
|
|
The surface Y coordinate of the center of the touching ellipse.
|
|
|
|
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]. 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. 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]. 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
|
|
-----------------
|
|
|
|
The flora of different hardware unavoidably leads to some devices fitting
|
|
better to the MT protocol than others. To simplify and unify the mapping,
|
|
this section gives recipes for how to compute certain events.
|
|
|
|
For devices reporting contacts as rectangular shapes, signed orientation
|
|
cannot be obtained. Assuming X and Y are the lengths of the sides of the
|
|
touching rectangle, here is a simple formula that retains the most
|
|
information possible:
|
|
|
|
ABS_MT_TOUCH_MAJOR := max(X, Y)
|
|
ABS_MT_TOUCH_MINOR := min(X, Y)
|
|
ABS_MT_ORIENTATION := bool(X > Y)
|
|
|
|
The range of ABS_MT_ORIENTATION should be set to [0, 1], to indicate that
|
|
the device can distinguish between a finger along the Y axis (0) and a
|
|
finger along the X axis (1).
|
|
|
|
|
|
Finger Tracking
|
|
---------------
|
|
|
|
The process of finger tracking, i.e., to assign a unique trackingID to each
|
|
initiated contact on the surface, is a Euclidian Bipartite Matching
|
|
problem. At each event synchronization, the set of actual contacts is
|
|
matched to the set of contacts from the previous synchronization. A full
|
|
implementation can be found in [3].
|
|
|
|
|
|
Gestures
|
|
--------
|
|
|
|
In the specific application of creating gesture events, the TOUCH and WIDTH
|
|
parameters can be used to, e.g., approximate finger pressure or distinguish
|
|
between index finger and thumb. With the addition of the MINOR parameters,
|
|
one can also distinguish between a sweeping finger and a pointing finger,
|
|
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.
|
|
|
|
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] The mtdev project: http://bitmath.org/code/mtdev/.
|
|
[4] See the section on event computation.
|
|
[5] See the section on finger tracking.
|