CODEWITHSUNDEEP
androidlinuxeventsinput
FranzKafka Yu
FranzKafka Yu

Reputation: 1

how to get the accurate coordinates from /dev/input/event0

I am working on handling input event by my own program in Android without Eventhub&InputReader,and the code worked in single-touch screen,while can't work in multi-touch screent,below are my codes(partialy):

 int readSize = read(mInputTouchfd, mEventData, EVS_READ_EVENT_MAX_NUM * sizeof(struct input_event));
    if (readSize >= (int)sizeof(struct input_event))
    {
        int eventNum = readSize / sizeof(struct input_event);
        LOG1("HandleTouchEvent has read %d input event", eventNum);
        for (int i = 0; i < eventNum; i++)
        {
            LOG1("number %d event,details:type:[0x%X] code:[0x%X (%d)] value:[0x%X]", i, mEventData[i].type, mEventData[i].code, mEventData[i].code, mEventData[i].value);
            if (mEventData[i].type == EV_ABS && mEventData[i].code == ABS_MT_POSITION_X)
            {
                realx = mEventData[i].value;
            }
            else if (mEventData[i].type == EV_ABS && mEventData[i].code == ABS_MT_POSITION_Y)
            {
                realy = mEventData[i].value;
            }
            else if (mEventData[i].type == EV_KEY && mEventData[i].code == BTN_TOUCH)
            {
                if (mEventData[i].value == TOUCH_EVENT_DOWN)
                {
                    buttonEvent = TOUCH_EVENT_DOWN;
                }
                else if (mEventData[i].value == TOUCH_EVENT_UP)
                {
                    buttonEvent = TOUCH_EVENT_UP;
                }
            }
            else if (mEventData[i].type == EV_SYN && mEventData[i].code == SYN_REPORT)
            {
                LOG1("parse Event succeed:Event[%s],x[%d],y[%d]", toString(buttonEvent), realx, realy);
                if (spHomePage)
                {
                    spHomePage->dispatchTouchEvent(buttonEvent, realx, realy);
                }
                // reset event type after handle finished
                buttonEvent = TOUCH_EVENT_MOVE;
            }
        }
    }

I have found that the event code,type,and value are different in multi-touch screen,I used getevent command to catch such events:

/dev/input/event0: EV_KEY       BTN_TOUCH            UP
/dev/input/event0: EV_MSC       MSC_TIMESTAMP        00032c80
/dev/input/event0: EV_SYN       SYN_REPORT           00000000
/dev/input/event0: EV_ABS       ABS_MT_TRACKING_ID   0000004d
/dev/input/event0: EV_ABS       ABS_MT_POSITION_X    00003dad
/dev/input/event0: EV_ABS       ABS_MT_POSITION_Y    000012bc
/dev/input/event0: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event0: EV_ABS       ABS_X                00003dad
/dev/input/event0: EV_ABS       ABS_Y                000012bc
/dev/input/event0: EV_MSC       MSC_TIMESTAMP        00034bc0
/dev/input/event0: EV_SYN       SYN_REPORT           00000000
/dev/input/event0: EV_MSC       MSC_TIMESTAMP        00036b00

when code=EV_ABS,type=ABS_MT_POSITION_X,the value is 00003dad(hex),equal to 15789(Dec),which is much bigger than 1920(my touch screen is 10 inCh,16:9 and 1080p,),I am confused how can I get the accurate coordinates（including x and y）？I think the value’s unit is Pixel while it seems not，anyone can help me？

I have searched ChatGPT/Google bard while I got the wrong answers.

Upvotes: 0

Views: 255

Answers (1)

FranzKafka Yu
FranzKafka Yu

Reputation: 1

Finally I found the answer for this question,in Android we can use getevent to get input protocol details including X/Y interval，for example:

a1000b:/ $ getevent -lp /dev/input/event0
add device 1: /dev/input/event0
  name:     "ILITEK ILITEK-TP"
  events:
    KEY (0001): BTN_TOUCH
    ABS (0003): ABS_X                 : value 11767, min 0, max 16384, fuzz 0, flat 0, resolution 34
                ABS_Y                 : value 2656, min 0, max 9600, fuzz 0, flat 0, resolution 36
                ABS_MT_SLOT           : value 0, min 0, max 9, fuzz 0, flat 0, resolution 0
                ABS_MT_POSITION_X     : value 0, min 0, max 16384, fuzz 0, flat 0, resolution 34
                ABS_MT_POSITION_Y     : value 0, min 0, max 9600, fuzz 0, flat 0, resolution 36
                ABS_MT_TRACKING_ID    : value 0, min 0, max 65535, fuzz 0, flat 0, resolution 0
    MSC (0004): MSC_TIMESTAMP
  input props:
    INPUT_PROP_DIRECT
a1000b:/ $

here we got X value interval：0-16384，Y value interval：0-9600； And we got events(also us getevent command) like this:

130|a1000b:/ $ getevent -l /dev/input/event0
EV_ABS       ABS_MT_TRACKING_ID   0000000b
EV_ABS       ABS_MT_POSITION_X    00002e95
EV_ABS       ABS_MT_POSITION_Y    00000f32
EV_KEY       BTN_TOUCH            DOWN
EV_ABS       ABS_X                00002e95
EV_ABS       ABS_Y                00000f32
EV_MSC       MSC_TIMESTAMP        00000000
EV_SYN       SYN_REPORT           00000000
EV_MSC       MSC_TIMESTAMP        00001f40

here we got x(ABS_MT_POSITION_X)=2e95(HEX),equals to 11925(DEC),and we translate to pixel(my screen is 1920*1080):

11925/16384*1920=1397.4609375≈1397，so can got X（in Pixel）is 1397，and the Y value is same calculation.

Upvotes: 0

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