input: mt: Document interface updates (22f075a8) · Commits · e / devices / android_kernel_fairphone_FP3

Documentation/input/multi-touch-protocol.txt

+26 −18

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


	Introduction		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		major and minor axis of an ellipse. Finally, the orientation of the oval
	shape can be describe with the ORIENTATION parameter.		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		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		finger or a pen or something else. Finally, the ABS_MT_TRACKING_ID event
	may specify general shapes as blobs, i.e., as a sequence of rectangular		may be used to track identified contacts over time [5].
	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		In the type B protocol, ABS_MT_TOOL_TYPE and ABS_MT_TRACKING_ID are
	report contact tracking from hardware [5].		implicitly handled by input core; drivers should instead call
			input_mt_report_slot_state().


	Event Semantics		Event Semantics
	@@ -247,21 +251,24 @@ ABS_MT_TOOL_TYPE
	The type of approaching tool. A lot of kernel drivers cannot distinguish		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		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		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		ABS_MT_BLOB_ID

	The BLOB_ID groups several packets together into one arbitrarily shaped		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		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.		devices do not have blob capability, so drivers can safely omit this event.

	ABS_MT_TRACKING_ID		ABS_MT_TRACKING_ID

	The TRACKING_ID identifies an initiated contact throughout its life cycle		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		[5]. The value range of the TRACKING_ID should be large enough to ensure
	TRACKING_ID should be large enough to ensure unique identification of a		unique identification of a contact maintained over an extended period of
	contact maintained over an extended period of time.		time. For type B devices, this event is handled by input core; drivers
			should instead use input_mt_report_slot_state().


	Event Computation		Event Computation
	@@ -308,18 +315,19 @@ and with ORIENTATION, one can detect twisting of fingers.
	Notes		Notes
	-----		-----

	In order to stay compatible with existing applications, the data		In order to stay compatible with existing applications, the data reported
	reported in a finger packet must not be recognized as single-touch		in a finger packet must not be recognized as single-touch events.
	events. In addition, all finger data must bypass input filtering,
	since subsequent events of the same type refer to different fingers.		For type A devices, all finger data bypasses input filtering, since
			subsequent events of the same type refer to different fingers.

	The first kernel driver to utilize the MT protocol is the bcm5974 driver,		For example usage of the type A protocol, see the bcm5974 driver. For
	where examples can be found.		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		[1] With the extension ABS_MT_APPROACH_X and ABS_MT_APPROACH_Y, the
	difference between the contact position and the approaching tool position		difference between the contact position and the approaching tool position
	could be used to derive tilt.		could be used to derive tilt.
	[2] The list can of course be extended.		[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.		[4] See the section on event computation.
	[5] See the section on finger tracking.		[5] See the section on finger tracking.