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Input: convert multi-touch protocol spec into ReST format
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This file require minimum adjustments to be a valid ReST file.
Do it, in order to be able to parse it with Sphinx

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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Mauro Carvalho Chehab authored and Dmitry Torokhov committed Apr 5, 2017
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200 changes: 96 additions & 104 deletions Documentation/input/multi-touch-protocol.txt
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.. include:: <isonum.txt>

=========================
Multi-touch (MT) Protocol
-------------------------
Copyright (C) 2009-2010 Henrik Rydberg <rydberg@euromail.se>
=========================

:Copyright: |copy| 2009-2010 Henrik Rydberg <rydberg@euromail.se>


Introduction
Expand Down Expand Up @@ -47,12 +51,12 @@ 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].
the raw data [#f5]_.

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].
important. Event filtering and finger tracking is left to user space [#f3]_.

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.
Expand Down Expand Up @@ -86,7 +90,7 @@ Protocol Example A
------------------

Here is what a minimal event sequence for a two-contact touch would look
like for a type A device:
like for a type A device::

ABS_MT_POSITION_X x[0]
ABS_MT_POSITION_Y y[0]
Expand All @@ -100,14 +104,14 @@ 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:
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:
And here is the sequence after lifting the second contact::

SYN_MT_REPORT
SYN_REPORT
Expand All @@ -122,7 +126,7 @@ Protocol Example B
------------------

Here is what a minimal event sequence for a two-contact touch would look
like for a type B device:
like for a type B device::

ABS_MT_SLOT 0
ABS_MT_TRACKING_ID 45
Expand All @@ -134,13 +138,13 @@ like for a type B device:
ABS_MT_POSITION_Y y[1]
SYN_REPORT

Here is the sequence after moving contact 45 in the x direction:
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:
Here is the sequence after lifting the contact in slot 0::

ABS_MT_TRACKING_ID -1
SYN_REPORT
Expand All @@ -149,7 +153,7 @@ 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:
Finally, here is the sequence after lifting the second contact::

ABS_MT_SLOT 1
ABS_MT_TRACKING_ID -1
Expand Down Expand Up @@ -181,6 +185,8 @@ 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.

::


Linux MT Win8
__________ _______________________
Expand Down Expand Up @@ -212,7 +218,7 @@ 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].
may be used to track identified contacts over time [#f5]_.

In the type B protocol, ABS_MT_TOOL_TYPE and ABS_MT_TRACKING_ID are
implicitly handled by input core; drivers should instead call
Expand All @@ -223,117 +229,103 @@ 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].
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 [#f4]_.

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].
The length, in surface units, of the minor axis of the contact. If the
contact is circular, this event can be omitted [#f4]_.

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].
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 [#f4]_.

ABS_MT_WIDTH_MINOR
The length, in surface units, of the minor axis of the approaching
tool. Omit if circular [#f4]_.

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.
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.

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.
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.
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 touching 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 an ellipse aligned with
the Y axis of the surface, a negative value when the ellipse is turned to
the left, and a positive value when the ellipse is turned to the
right. When completely aligned with the X axis, the range max should be
returned.

Touch ellipsis are symmetrical by default. For devices capable of true 360
degree orientation, the reported orientation must exceed the range max to
indicate more than a quarter of a revolution. For an upside-down finger,
range max * 2 should be returned.

Orientation can be omitted if the touch area 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].
The orientation of the touching 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 an ellipse aligned with
the Y axis of the surface, a negative value when the ellipse is turned to
the left, and a positive value when the ellipse is turned to the
right. When completely aligned with the X axis, the range max should be
returned.

Touch ellipsis are symmetrical by default. For devices capable of true 360
degree orientation, the reported orientation must exceed the range max to
indicate more than a quarter of a revolution. For an upside-down finger,
range max * 2 should be returned.

Orientation can be omitted if the touch area 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] [#f4]_.

ABS_MT_POSITION_X

The surface X coordinate of the center of the touching ellipse.
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.
The surface Y coordinate of the center of the touching ellipse.

ABS_MT_TOOL_X

The surface X coordinate of the center of the approaching tool. Omit if
the device cannot distinguish between the intended touch point and the
tool itself.
The surface X coordinate of the center of the approaching tool. Omit if
the device cannot distinguish between the intended touch point and the
tool itself.

ABS_MT_TOOL_Y
The surface Y coordinate of the center of the approaching tool. Omit if the
device cannot distinguish between the intended touch point and the tool
itself.

The surface Y coordinate of the center of the approaching tool. Omit if the
device cannot distinguish between the intended touch point and the tool
itself.

The four position values can be used to separate the position of the touch
from the position of the tool. If both positions are present, the major
tool axis points towards the touch point [1]. Otherwise, the tool axes are
aligned with the touch axes.
The four position values can be used to separate the position of the touch
from the position of the tool. If both positions are present, the major
tool axis points towards the touch point [#f1]_. Otherwise, the tool axes are
aligned with the touch axes.

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,
MT_TOOL_PEN, and MT_TOOL_PALM [2]. For type B devices, this event is handled
by input core; drivers should instead use input_mt_report_slot_state().
A contact's ABS_MT_TOOL_TYPE may change over time while still touching the
device, because the firmware may not be able to determine which tool is being
used when it first appears.
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,
MT_TOOL_PEN, and MT_TOOL_PALM [#f2]_. For type B devices, this event is
handled by input core; drivers should instead use
input_mt_report_slot_state(). A contact's ABS_MT_TOOL_TYPE may change over
time while still touching the device, because the firmware may not be able
to determine which tool is being used when it first appears.

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.
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 [#f5]_. 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().
The TRACKING_ID identifies an initiated contact throughout its life cycle
[#f5]_. 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
Expand All @@ -346,7 +338,7 @@ 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:
information possible::

ABS_MT_TOUCH_MAJOR := max(X, Y)
ABS_MT_TOUCH_MINOR := min(X, Y)
Expand All @@ -356,7 +348,7 @@ 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).

For win8 devices with both T and C coordinates, the position mapping is
For win8 devices with both T and C coordinates, the position mapping is::

ABS_MT_POSITION_X := T_X
ABS_MT_POSITION_Y := T_Y
Expand All @@ -365,7 +357,7 @@ For win8 devices with both T and C coordinates, the position mapping is

Unfortunately, there is not enough information to specify both the touching
ellipse and the tool ellipse, so one has to resort to approximations. One
simple scheme, which is compatible with earlier usage, is:
simple scheme, which is compatible with earlier usage, is::

ABS_MT_TOUCH_MAJOR := min(X, Y)
ABS_MT_TOUCH_MINOR := <not used>
Expand All @@ -386,7 +378,7 @@ 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].
implementation can be found in [#f3]_.


Gestures
Expand All @@ -411,8 +403,8 @@ 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] Also, the difference (TOOL_X - POSITION_X) can be used to model 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.
.. [#f1] Also, the difference (TOOL_X - POSITION_X) can be used to model tilt.
.. [#f2] The list can of course be extended.
.. [#f3] The mtdev project: http://bitmath.org/code/mtdev/.
.. [#f4] See the section on event computation.
.. [#f5] See the section on finger tracking.

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