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androidadbtouch

How to interpret getevent touch coordinates as actual touch coordinates

Taken from the source file itself:

#define ABS_MT_POSITION_X   0x35    /* Center X ellipse position */
#define ABS_MT_POSITION_Y   0x36    /* Center Y ellipse position */

So when I get an output:

/dev/input/event2: 0003 0039 00000cc7
/dev/input/event2: 0001 014a 00000001
/dev/input/event2: 0001 0145 00000001
/dev/input/event2: 0003 0035 00000a2d  //<---- X coordinate
/dev/input/event2: 0003 0036 00000e6c  //<---- Y coordinate
/dev/input/event2: 0003 0030 00000008
/dev/input/event2: 0003 0031 00000008
/dev/input/event2: 0003 003e 0001017e
/dev/input/event2: 0000 0000 00000000
/dev/input/event2: 0003 003e 00000000
/dev/input/event2: 0003 0039 ffffffff
/dev/input/event2: 0001 014a 00000000
/dev/input/event2: 0001 0145 00000000
/dev/input/event2: 0000 0000 00000000

a2d to decimal is 2605 and e6c is 3692. The position, actually was (670,2141) on the screen. How can I convert the getevent coordinates to actual usable coordinates.

Plus, what exactly does "Center X ellipse position" and "Center Y ellipse position" mean?

Any help is appreciated.

EDIT: I touched the right bottom of the screen and the getevent output was:

/dev/input/event2: EV_ABS       ABS_MT_TRACKING_ID   00000d4f
/dev/input/event2: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event2: EV_KEY       BTN_TOOL_FINGER      DOWN
/dev/input/event2: EV_ABS       ABS_MT_POSITION_X    00000f86 #<---X coordinate
/dev/input/event2: EV_ABS       ABS_MT_POSITION_Y    00000f9d //<---Y coordinate
/dev/input/event2: EV_ABS       003e                 0001017e
/dev/input/event2: EV_SYN       SYN_REPORT           00000000
/dev/input/event2: EV_ABS       003e                 00000000
/dev/input/event2: EV_ABS       ABS_MT_TRACKING_ID   ffffffff
/dev/input/event2: EV_KEY       BTN_TOUCH            UP
/dev/input/event2: EV_KEY       BTN_TOOL_FINGER      UP
/dev/input/event2: EV_SYN       SYN_REPORT           00000000

Here, f86 = 3974and f9d = 3997. And the actual size of the screen is around (1057,2366) (approximately).

So I thought maybe it just uses proportions, instead of actual values. So basically if we do (co-ordinate given by getevent/ max coordinate size for getevent) * (Actual coordinate size), we might get the correct value.

And I did exactly that, and got correct values. (2905/3974)*1057 = 692 and (3692/3997)*2366 = 2185, both of which are close to the actual values.

So now the question becomes, is the canvas size always equal to (4000,4000)?

Solution

  • In order to use the X,Y coordinates provided by getevent into input tap x y, we need to do the following things:

    1. Find out max X,Y for getevent by getevent -il /dev/input/event2 | grep ABS_MT_POSITION. That gave be (4000,4000)
    2. Find out the actual screen size by adb shell wm size this gave me (1080,2400)
    3. Now convert getevent (x,y) into (x*1080/4000,y*2400/4000) to get the actual results, which can be used with input tap x y.