evdev touch points viewer

evdev-multi-touch-viewer.py

# needs root.

from evdev import InputDevice, categorize, ecodes

# input device (right one is nice to find using sudo evemu-describe)
dev = InputDevice('/dev/input/event14')

print(dev)

# list of x, y tuples
touches_supported = 10
touches = [(-1, -1) for _ in range(touches_supported)]

slot = 0
for event in dev.read_loop():
  
    # react to slot changes
    if event.code == ecodes.ABS_MT_SLOT:
        slot = event.value
        
    # set coordinates on right slot
    if event.type == ecodes.EV_ABS:
        if event.code == ecodes.ABS_MT_POSITION_X:
            x = event.value
            touches[slot] = (x, touches[slot][1])
        if event.code == ecodes.ABS_MT_POSITION_Y:
            y = event.value
            touches[slot] = (touches[slot][0], y)
            
        print(touches)

    # reset coordinates (tracking id becomes -1 with a switch to the respective slot beforehand)
    if event.code == ecodes.ABS_MT_TRACKING_ID and event.value == -1:
        touches[slot] = (-1, -1)
        print(touches)