Huion GT-191 hack, see https://github.com/benthor/HuionKamvasGT191LinuxDriver

kamvas.py

import os
import sys
from evdev import UInput, ecodes, AbsInfo

PEN_MAX_X = 1 << 16 - 1
PEN_MAX_Y = 1 << 16 - 1
PEN_MAX_Z = 8191
RESOLUTION = 5080

#pressure sensitive pen tablet area with 2 stylus buttons and no eraser
cap_pen = {
    ecodes.EV_KEY: [ecodes.BTN_TOUCH, ecodes.BTN_TOOL_PEN, ecodes.BTN_STYLUS, ecodes.BTN_STYLUS2],
    ecodes.EV_ABS: [
        (ecodes.ABS_X, AbsInfo(0,0,PEN_MAX_X,0,0,RESOLUTION)), #value, min, max, fuzz, flat, resolution
        (ecodes.ABS_Y, AbsInfo(0,0,PEN_MAX_Y,0,0,RESOLUTION)),
        (ecodes.ABS_PRESSURE, AbsInfo(0,0,PEN_MAX_Z,0,0,0)),
    ],
    #ecodes.EV_MSC: [ecodes.MSC_SCAN], #not sure why, but it appears to be needed
}

vpen = UInput(events=cap_pen, name="kamvas-pen", version=0x3)
with os.popen('usbhid-dump -t0 -es -m 256c:006e') as p:
    for line in p:
        # example data line:
        #  0A 80 EA 5A D2 6B 00 00
        if line[0] != ' ':
            continue
        data = [int(x, base=16) for x in line.split()]
        print(','.join(map(str, data)))
        X = (data[3] << 8) + data[2]
        Y = (data[5] << 8) + data[4]
        PRESS = (data[7] << 8) + data[6]
        TOUCH = data[1] == 193
        BTN1 = data[1] == 194
        BTN2 = data[1] == 196
        print("X %6d Y%6d PRESS %4d (%s %s %s))" % (X, Y, PRESS, TOUCH, BTN1, BTN2))
        vpen.write(ecodes.EV_ABS, ecodes.ABS_X, X)
        vpen.write(ecodes.EV_ABS, ecodes.ABS_Y, Y)
        vpen.write(ecodes.EV_ABS, ecodes.ABS_PRESSURE, PRESS)
        vpen.write(ecodes.EV_KEY, ecodes.BTN_TOUCH, TOUCH and 1 or 0)
        vpen.write(ecodes.EV_KEY, ecodes.BTN_STYLUS, BTN1 and 1 or 0)
        vpen.write(ecodes.EV_KEY, ecodes.BTN_STYLUS2, BTN2 and 1 or 0)
        vpen.syn()