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4 Multi-touch (MT) Protocol
7 :Copyright: |copy| 2009-2010 Henrik Rydberg <rydberg@euromail.se>
11 ------------
13 In order to utilize the full power of the new multi-touch and multi-user
16 document describes the multi-touch (MT) protocol which allows kernel
30 --------------
34 packet. Since these events are ignored by current single-touch (ST)
48 All drivers mark the end of a multi-touch transfer by calling the usual
67 the ABS_MT_TRACKING_ID of the associated slot. A non-negative tracking id
68 is interpreted as a contact, and the value -1 denotes an unused slot. A
88 total number of type B slots reported in the absinfo for the ABS_MT_SLOT axis.
90 The minimum value of the ABS_MT_SLOT axis must be 0.
93 ------------------
95 Here is what a minimal event sequence for a two-contact touch would look
98 ABS_MT_POSITION_X x[0]
101 ABS_MT_POSITION_X x[1]
112 ABS_MT_POSITION_X x[1]
125 zero-contact event reaching userland.
129 ------------------
131 Here is what a minimal event sequence for a two-contact touch would look
136 ABS_MT_POSITION_X x[0]
140 ABS_MT_POSITION_X x[1]
144 Here is the sequence after moving contact 45 in the x direction::
147 ABS_MT_POSITION_X x[0]
152 ABS_MT_TRACKING_ID -1
162 ABS_MT_TRACKING_ID -1
167 -----------
186 than unity, is related to the contact pressure. For pressure-based devices,
215 and MINOR are the major and minor axis of an ellipse. The orientation of
217 direction of the finger ellipse is given by the vector (a - b).
232 ---------------
235 The length of the major axis of the contact. The length should be given in
236 surface units. If the surface has an X times Y resolution, the largest
237 possible value of ABS_MT_TOUCH_MAJOR is sqrt(X^2 + Y^2), the diagonal [#f4]_.
240 The length, in surface units, of the minor axis of the contact. If the
244 The length, in surface units, of the major axis of the approaching
250 The length, in surface units, of the minor axis of the approaching
260 of TOUCH and WIDTH for pressure-based devices or any device with a spatial
264 If the resolution is non-zero, the pressure data is in units/gram. See
265 :ref:`input-event-codes` for details.
276 the Y axis (north) of the surface, a negative value when the ellipse is
278 right. When aligned with the X axis in the positive direction, the range
279 max should be returned; when aligned with the X axis in the negative
280 direction, the range -max should be returned.
284 indicate more than a quarter of a revolution. For an upside-down finger,
294 The surface X coordinate of the center of the touching ellipse.
300 The surface X coordinate of the center of the approaching tool. Omit if
311 tool axis points towards the touch point [#f1]_. Otherwise, the tool axes are
327 the contact. This is a low-level anonymous grouping for type A devices, and
328 should not be confused with the high-level trackingID [#f5]_. Most type A
340 -----------------
347 cannot be obtained. Assuming X and Y are the lengths of the sides of the
351 ABS_MT_TOUCH_MAJOR := max(X, Y)
352 ABS_MT_TOUCH_MINOR := min(X, Y)
353 ABS_MT_ORIENTATION := bool(X > Y)
356 the device can distinguish between a finger along the Y axis (0) and a
357 finger along the X axis (1).
370 ABS_MT_TOUCH_MAJOR := min(X, Y)
373 ABS_MT_WIDTH_MAJOR := min(X, Y) + distance(T, C)
374 ABS_MT_WIDTH_MINOR := min(X, Y)
378 ellipse should align with the vector (T - C), so the diameter must
383 ---------------
393 --------
403 -----
406 in a finger packet must not be recognized as single-touch events.
411 .. [#f1] Also, the difference (TOOL_X - POSITION_X) can be used to model tilt.