1， 两种多点触摸协议：

• A类： 处理无关联的接触： 用于直接发送原始数据；
  
• B类： 处理跟踪识别类的接触： 通过事件slot发送相关联的独立接触更新。

2， 触摸协议的使用：

A类协议：

A类协议在每发送完一个接触数据包后会调用 input_mt_sync() 声明 一次数据的结束； input_mt_sync() 会发出一个 SYN_MT_REPORT

B类协议：

与A类协议不同的是， B类在使用input_mt_slot()的时候会带有一个slot的参数，在每个数据包开始时 产生一个ABS_MT_SLOT事件，提示接收器更新数据。

最终A，B类协议均会调用 input_sync();

A类与B类协议不同的在于： B类协议 通过B类协议 slot 协议需要是用到ABS_MT_TRACKING_ID------ 可以从硬件上获取，或者从原始数据中计算。

3, B类协议：

ABS_MT_TRACKING_ID 表示一次接触； -1 代表一个不用的slot；

使用参考例子：

释放事件：

input_mt_slot(data->input_dev, i);
input_mt_report_slot_state(data->input_dev, MT_TOOL_FINGER, false);

点击事件：

input_mt_slot(data->input_dev, i);
input_mt_report_slot_state(data->input_dev, MT_TOOL_FINGER, true);
input_report_abs(data->input_dev, ABS_MT_TOUCH_MAJOR, 1);
input_report_abs(data->input_dev, ABS_MT_POSITION_X, current_events[i].x);
input_report_abs(data->input_dev, ABS_MT_POSITION_Y, current_events[i].y)

补充: 不同事件的标记： 备忘。

ABS_MT_TOUCH_MAJOR

             The length of the major axis of the contact. The length should be given insurface units. If the surface has an X times Y resolution, the largestpossible 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 thecontact is circular, this event can be omitted [4].

ABS_MT_WIDTH_MAJOR

             The length, in surface units, of the major axis of the approachingtool. This should be understood as the size of the tool itself. Theorientation of the contact and the approaching tool are assumed to be thesame [4].

ABS_MT_WIDTH_MINOR

            The length, in surface units, of the minor axis of the approachingtool. Omit if circular [4].The above four values can be used to derive additional information aboutthe contact. The ratio ABS_MT_TOUCH_MAJOR / ABS_MT_WIDTH_MAJOR approximatesthe notion of pressure. The fingers of the hand and the palm all havedifferent characteristic widths [1].

ABS_MT_PRESSURE

            The pressure, in arbitrary units, on the contact area. May be used insteadof TOUCH and WIDTH for pressure-based devices or any device with a spatialsignal intensity distribution.

ABS_MT_DISTANCE

           The distance, in surface units, between the contact and the surface. Zerodistance means the contact is touching the surface. A positive number meansthe contact is hovering above the surface.

ABS_MT_ORIENTATION

           The orientation of the ellipse. The value should describe a signed quarterof a revolution clockwise around the touch center. The signed value rangeis arbitrary, but zero should be returned for a finger aligned along the Yaxis of the surface, a negative value when finger is turned to the left, anda positive value when finger turned to the right. When completely aligned withthe X axis, the range max should be returned. Orientation can be omittedif the touching object is circular, or if the information is not availablein the ker