Android absolute mouse

absmouse.c

/*
 * Android (and Linux X11) can't handle absolute position HID events from mouse
 * https://www.codeproject.com/Articles/1001891/A-USB-HID-Keyboard-Mouse-Touchscreen-emulator-with
 *
 * This program read these ABS_X & ABS_Y events from /dev/input/eventX, and emulate a touchscreen/stylus via linux uinput, so an "absolute" mouse can work.
 * Example of "absolute" mouse: PiKVM, or some other mouse-emulating hardware (e.g. https://detail.tmall.com/item.htm?id=684263217981)
 */

#include <linux/uinput.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// An "absolute" mouse is sending events to "/dev/input/event12"
#define EVENT_SRC "/dev/input/event12"

// My device is Sony Xperia 5 II which has a 2520x1080 display
#define ABS_X_MAX 2520
#define ABS_Y_MAX 1080

// My absolute mouse assumes a different aspect ratio, so we need a manual transform here
#define TRANSFORM_ABS_X(x) (x * 1920 / 0x1fff + 300)
#define TRANSFORM_ABS_Y(y) (y * 1080 / 0xfff)

void emit(int fd, int type, int code, int val)
{
    struct input_event ie;

    ie.type = type;
    ie.code = code;
    ie.value = val;
    /* timestamp values below are ignored */
    ie.time.tv_sec = 0;
    ie.time.tv_usec = 0;

    write(fd, &ie, sizeof(ie));
}

int main(void)
{
    struct uinput_setup usetup;
    struct uinput_abs_setup uabs;

    int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);

    ioctl(fd, UI_SET_EVBIT, EV_KEY);
    /*
     * BTN_TOUCH is neccessary for Android to recognize it as a touchscreen device.
     * https://source.android.com/docs/core/interaction/input/touch-devices
     */
    ioctl(fd, UI_SET_KEYBIT, BTN_TOUCH);
    ioctl(fd, UI_SET_KEYBIT, BTN_TOOL_PEN);

    // Regular android buttons
    ioctl(fd, UI_SET_KEYBIT, BTN_LEFT);
    ioctl(fd, UI_SET_KEYBIT, BTN_RIGHT);
    ioctl(fd, UI_SET_KEYBIT, BTN_MIDDLE);
    ioctl(fd, UI_SET_KEYBIT, BTN_SIDE);
    ioctl(fd, UI_SET_KEYBIT, BTN_EXTRA);

    /*
     * Only touchscreen devices (instead of mouse) support EV_ABS (ABS_X/ABS_Y)
     */
    ioctl(fd, UI_SET_EVBIT, EV_ABS);
    ioctl(fd, UI_SET_ABSBIT, ABS_X);
    ioctl(fd, UI_SET_ABSBIT, ABS_Y);

    ioctl(fd, UI_SET_EVBIT, EV_REL);
    ioctl(fd, UI_SET_RELBIT, REL_WHEEL);

    // Still need a pointer on the screen
    ioctl(fd, UI_SET_PROPBIT, INPUT_PROP_POINTER);

    uabs.code = ABS_X;
    uabs.absinfo.minimum = 0;
    uabs.absinfo.maximum = ABS_X_MAX;
    ioctl(fd, UI_ABS_SETUP, &uabs);

    uabs.code = ABS_Y;
    uabs.absinfo.minimum = 0;
    uabs.absinfo.maximum = ABS_Y_MAX;
    ioctl(fd, UI_ABS_SETUP, &uabs);

    memset(&usetup, 0, sizeof(usetup));
    usetup.id.bustype = BUS_USB;
    usetup.id.vendor = 0x1234;
    usetup.id.product = 0x5678;
    strcpy(usetup.name, "Virtual device");

    ioctl(fd, UI_DEV_SETUP, &usetup);
    ioctl(fd, UI_DEV_CREATE);

    int src_fd = open(EVENT_SRC, O_RDONLY);
    struct input_event src_ev;

    int n;
    while ((n = read(src_fd, &src_ev, sizeof(src_ev))))
    {
        if (n != sizeof(src_ev))
        {
            fprintf(stderr, "error reading events from src: %d", n);
            close(src_fd);
            sleep(1);

            // Try again
            src_fd = open(EVENT_SRC, O_RDONLY);
        }

        // Always send BTN_TOOL_PEN to indicate the virtual "pen" is hovering near to screen
        emit(fd, EV_KEY, BTN_TOOL_PEN, 1);

        if (src_ev.type == EV_KEY &&
            (src_ev.code == BTN_LEFT ||
             src_ev.code == BTN_RIGHT ||
             src_ev.code == BTN_MIDDLE))
        {
            // Send BTN_TOUCH to indicate the virtual "pen" is touching the screen
            emit(fd, EV_KEY, src_ev.value ? src_ev.code : BTN_TOUCH, src_ev.value);
            emit(fd, EV_KEY, src_ev.value ? BTN_TOUCH : src_ev.code, src_ev.value);
        }
        else if (src_ev.type == EV_KEY && (src_ev.code == BTN_SIDE || src_ev.code == BTN_EXTRA))
        {
            emit(fd, EV_KEY, src_ev.code, src_ev.value);
        }
        else if (src_ev.type == EV_ABS && (src_ev.code == ABS_X || src_ev.code == ABS_Y))
        {
            if (src_ev.code == ABS_X)
                emit(fd, EV_ABS, ABS_X, TRANSFORM_ABS_X(src_ev.value));
            if (src_ev.code == ABS_Y)
                emit(fd, EV_ABS, ABS_Y, TRANSFORM_ABS_Y(src_ev.value));
        }
        else if (src_ev.type == EV_SYN)
        {
            emit(fd, EV_SYN, SYN_REPORT, 0);
        }
        else if (src_ev.type == EV_REL && src_ev.code == REL_WHEEL)
        {
            emit(fd, EV_REL, REL_WHEEL, src_ev.value);
        }
        else
        {
            fprintf(stderr, "unrecognized event: %d %d %d\n", src_ev.type, src_ev.code, src_ev.value);
        }
    }

    // int i = 0;
    // while (i++ < 200)
    // {
    //     printf("i: %d\n", i);
    //     emit(fd, EV_KEY, BTN_TOOL_PEN, 1);
    //     emit(fd, EV_ABS, ABS_X, 300 + i);
    //     emit(fd, EV_ABS, ABS_Y, i);
    //     emit(fd, EV_SYN, SYN_REPORT, 0);
    //     usleep(15 * 1000);
    // }

    // emit(fd, EV_KEY, BTN_LEFT, 1);
    // emit(fd, EV_KEY, BTN_TOUCH, 1);
    // emit(fd, EV_SYN, SYN_REPORT, 0);
    // usleep(15 * 1000);

    // emit(fd, EV_KEY, BTN_TOUCH, 0);
    // emit(fd, EV_KEY, BTN_LEFT, 0);
    // emit(fd, EV_SYN, SYN_REPORT, 0);

    ioctl(fd, UI_DEV_DESTROY);
    close(fd);

    return 0;
}