evdev touch viewer

evdev-touch-viewer-gui.py

import sys
import tkinter
import time
try:
    from evdev import InputDevice, categorize, ecodes
except ImportError:
    print("This script requires the evdev package (https://pypi.org/project/evdev/). ")
    exit()

try:
    dev_path = sys.argv[1]
    dev = InputDevice(dev_path)
except (OSError, FileNotFoundError, IndexError):
    print("Provide the path to a touch input device (looks like /dev/input/event0 and can be identified using evemu-describe) and run the script as root. ")
    exit()

print(dev)

# normalization
max_x = dev.absinfo(0).max
max_y = dev.absinfo(1).max

# init window
window = tkinter.Tk()
window.title("Touches")
window_width = 1024
canvas = tkinter.Canvas(window, width=window_width,height=window_width/(max_x/max_y))

last_paint = time.time()
# update window


def draw(window, canvas, touches, override_skip=False):
    global last_paint

    t = time.time()
    if t-last_paint < 0.0003 and not override_skip:
        # print("Skipped")
        return

    print(touches)

    canvas.delete(tkinter.ALL)

    i = 1
    for touch in touches:
        touch_color = "#%02x%02x%02x" % (i*80 % 255, i*220 % 255, i*190 % 255)
        if touch[0] != -1 and touch[1] != -1:
            x = touch[0]*canvas.winfo_width()
            y = touch[1]*canvas.winfo_width()

            canvas.create_oval(x, y, x+20, y+20, fill=touch_color)
        i += 1

    canvas.pack()
    window.update()
    last_paint = time.time()


draw(window, canvas, [])

# 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 / max_x, touches[slot][1])
        if event.code == ecodes.ABS_MT_POSITION_Y:
            y = event.value
            touches[slot] = (touches[slot][0], y / max_x)
        draw(window, canvas, touches)

    # reset coordinates (tracking id becomes -1 with a switch to the respective slot before hand)
    if event.code == ecodes.ABS_MT_TRACKING_ID and event.value == -1:
        touches[slot] = (-1, -1)
        draw(window, canvas, touches, override_skip=True)