Reading multitouch using libevdev - c

Question

I'm trying to read raw multitouch data from my touchpad, though I'm not getting the results I expect.
I started by identifying what my device ID was, using lsinput:
/dev/input/event0
bustype : BUS_HOST
vendor : 0x0
product : 0x5
version : 0
name : "Lid Switch"
phys : "PNP0C0D/button/input0"
bits ev : EV_SYN EV_SW
/dev/input/event1
bustype : BUS_HOST
vendor : 0x0
product : 0x1
version : 0
name : "Power Button"
phys : "PNP0C0C/button/input0"
bits ev : EV_SYN EV_KEY
/dev/input/event2
bustype : BUS_HOST
vendor : 0x0
product : 0x1
version : 0
name : "Power Button"
phys : "LNXPWRBN/button/input0"
bits ev : EV_SYN EV_KEY
/dev/input/event3
bustype : BUS_I8042
vendor : 0x1
product : 0x1
version : 43907
name : "AT Translated Set 2 keyboard"
phys : "isa0060/serio0/input0"
bits ev : EV_SYN EV_KEY EV_MSC EV_LED EV_REP
/dev/input/event4
bustype : BUS_HOST
vendor : 0x0
product : 0x6
version : 0
name : "Video Bus"
phys : "LNXVIDEO/video/input0"
bits ev : EV_SYN EV_KEY
/dev/input/event5
bustype : BUS_HOST
vendor : 0x0
product : 0x6
version : 0
name : "Video Bus"
phys : "LNXVIDEO/video/input0"
bits ev : EV_SYN EV_KEY
/dev/input/event6
bustype : BUS_I8042
vendor : 0x2
product : 0x7
version : 433
name : "SynPS/2 Synaptics TouchPad"
phys : "isa0060/serio1/input0"
bits ev : EV_SYN EV_KEY EV_ABS
/dev/input/event7
bustype : BUS_HOST
vendor : 0x0
product : 0x0
version : 0
name : "Ideapad extra buttons"
phys : "ideapad/input0"
bits ev : EV_SYN EV_KEY EV_MSC
/dev/input/event8
bustype : BUS_USB
vendor : 0x4f2
product : 0xb57e
version : 34624
name : "EasyCamera: EasyCamera"
phys : "usb-0000:00:14.0-6/button"
bits ev : EV_SYN EV_KEY
/dev/input/event9
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH Mic"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event10
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH Headphone"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event11
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH HDMI/DP,pcm=3"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event12
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH HDMI/DP,pcm=7"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event13
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH HDMI/DP,pcm=8"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event14
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH HDMI/DP,pcm=9"
phys : "ALSA"
bits ev : EV_SYN EV_SW
/dev/input/event15
bustype : (null)
vendor : 0x0
product : 0x0
version : 0
name : "HDA Intel PCH HDMI/DP,pcm=10"
phys : "ALSA"
bits ev : EV_SYN EV_SW
Since I could see none of the devices listed here, I decided to choose /dev/input/event6 (SynPS/2 Synaptics TouchPad) which seemed the closest to what I was looking for.
Now, I've written a dead-simple code to try and get the max number of MT points from it:
int main(void)
{
struct libevdev *dev;
int fd;
int rc;
fd = open("/dev/input/event6", O_RDONLY|O_NONBLOCK);
if (fd < 0)
fprintf(stderr, "error: %d %s\n", errno, strerror(errno));
rc = libevdev_new_from_fd(fd, &dev);
if (rc < 0)
fprintf(stderr, "error: %d %s\n", -rc, strerror(-rc));
int n = libevdev_get_num_slots(dev);
printf("%d\n", n);
return 0;
}
I can compile it using gcc -levdev myfile.c and run it properly, but I only get 2.
Does that mean that my touchpad only handles two points ? This is weird, since it can handle (at least) 4 on Windows.
Do you have any ideas about this?
Small update : using libinput-debug-events, I get the following output
When using 1 finger:
event6 POINTER_MOTION +0.79s 0.00/ -6.22
event6 POINTER_MOTION +0.80s 0.00/-11.26
event6 POINTER_MOTION +0.81s 0.00/ -9.93
event6 POINTER_MOTION +0.82s 1.69/ -9.05
When using 2 fingers:
event6 POINTER_AXIS +0.60s vert -9.27* horiz 1.19* (finger)
event6 POINTER_AXIS +0.62s vert -13.25* horiz 2.03* (finger)
event6 POINTER_AXIS +0.65s vert -15.89* horiz 2.03* (finger)
When using 3 fingers:
event6 GESTURE_PINCH_UPDATE +0.68s 4 1.42/-1.54 ( 5.49/-5.97 unaccelerated) 0.99 # 0.15
event6 GESTURE_PINCH_UPDATE +0.71s 4 0.00/-0.31 ( 0.00/-0.89 unaccelerated) 0.99 # 0.07
event6 GESTURE_PINCH_UPDATE +0.73s 4 1.03/-3.44 ( 3.20/-10.74 unaccelerated) 0.98 # 0.74
When using 4 fingers:
event6 GESTURE_SWIPE_UPDATE +0.80s 4 0.00/-0.89 ( 0.00/-6.86 unaccelerated)
event6 GESTURE_SWIPE_UPDATE +0.82s 4 0.00/-1.18 ( 0.00/-7.16 unaccelerated)
event6 GESTURE_SWIPE_UPDATE +0.84s 4 0.68/-3.48 ( 3.20/-16.40 unaccelerated)
So it does seem that there's something on my system that is capable of detecting and reading at least up to four fingers... But for some reason, I can't get them with libevdev...