Evdev long click to right click emulation

README.md

A Python script to implement long-click-to-right-click emulation on Linux. Root permission needed (or you need udev rules to allow your user to write / read from evdev)

Usage:

python rce.py <name_of_your_tuchscreen>

Use xinput output to determine the name of your touchscreen

Environment variable RCE_SCALE is used to set the scale factor of your touchscreen. (your touchscreen resolution can be significantly higher than your actual screen resolution, and your screen may also have high DPI). This will enlarge the allowed error threshold (when long-pressing you can't avoid some slight movement).

On surface pro 6 I set RCE_SCALE=6.

Note: This evdev is different from the Xorg notion of the evdev driver. You are perfectly fine if your Xorg configuration uses libinput.

rce.py

#!/usr/bin/env python
import asyncio
from evdev import InputDevice, UInput, KeyEvent, ecodes
import evdev
import os
import sys
import subprocess
import time

async def main():
  for path in evdev.list_devices():
    dev = InputDevice(path)
    if dev.name == sys.argv[1]:
      await simulate_right_click(dev)
      return
  # Device not found
  sys.stderr.write("Failed to detect the specified device.\n")
  exit(1)

async def simulate_right_click(dev):
  scale_factor = int(os.environ['RCE_SCALE'])
  threshold = 80 * scale_factor
  min_interval = 0.5
  pos_x = -1
  pos_y = -1
  pos_last_x = -1
  pos_last_y = -1
  idev_caps = {
      ecodes.EV_REL: (ecodes.REL_X, ecodes.REL_Y),
      ecodes.EV_KEY: (ecodes.BTN_RIGHT, ecodes.BTN_TOUCH)
  }
  idev = UInput(idev_caps)
  trigger_task = None
  # The task function used to trigger right clicks
  async def trigger_right_click():
    await asyncio.sleep(min_interval)
    dX = abs(pos_last_x - pos_x)
    dY = abs(pos_last_y - pos_y)
    if dX <= threshold and dY <= threshold:
      idev.write(ecodes.EV_REL, ecodes.REL_X, 1)
      idev.write(ecodes.EV_REL, ecodes.REL_Y, 1)
      idev.write(ecodes.EV_KEY, ecodes.BTN_TOUCH, 0)
      idev.syn()
      idev.write(ecodes.EV_KEY, ecodes.BTN_RIGHT, 1)
      idev.syn()
      idev.write(ecodes.EV_KEY, ecodes.BTN_RIGHT, 0)
      idev.syn()
    trigger_task = None

  async for ev in dev.async_read_loop():
    if ev.type == ecodes.EV_ABS:
      abs_type = ecodes.ABS[ev.code]
      # Track the position of touch
      # Note that this position is not 1:1 to the screen resolution
      if abs_type == "ABS_X" or abs_type == "ABS_MT_POSITION_X":
        pos_x = ev.value
      elif abs_type == "ABS_Y" or abs_type == "ABS_MT_POSITION_Y":
        pos_y = ev.value
    elif ev.type == ecodes.EV_KEY:
      tev = KeyEvent(ev)
      if tev.keycode == 'BTN_TOUCH':
        if tev.keystate == KeyEvent.key_down:
          if trigger_task != None:
            trigger_task.cancel()
          trigger_task = asyncio.get_event_loop().create_task(trigger_right_click())
          pos_last_x = pos_x
          pos_last_y = pos_y
        elif tev.keystate == KeyEvent.key_up:
          if trigger_task != None:
            trigger_task.cancel()
          
  idev.close()

asyncio.get_event_loop().run_until_complete(main())
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