Alt + mouse move to scroll

README.md

Let users to press alt+mouse move to scroll to the target position, keep the mouse at the current position. Useful for trackball users who want the ability to scroll easily.

How to use: Just run this script, tested with Linux. Didn't check with Windows yet but should works on Windows too. You can add it to the startup application, eg. via .zshrc

win-scroll.py

#!/usr/bin/env python3
from pynput import keyboard, mouse

# --- CONFIGURATION ---
SENSITIVITY = 10  # Lower = Faster
# ---------------------

m = mouse.Controller()
anchor_pos = None
accumulator = 0
modifier_held = False

def on_key_press(key):
    global anchor_pos, accumulator, modifier_held
    # Check for either Left Alt or Right Alt
    if key in (keyboard.Key.alt, keyboard.Key.alt_l, keyboard.Key.alt_r):
        if anchor_pos is None:
            anchor_pos = m.position
            accumulator = 0
            modifier_held = True

def on_key_release(key):
    global anchor_pos, modifier_held
    if key in (keyboard.Key.alt, keyboard.Key.alt_l, keyboard.Key.alt_r):
        anchor_pos = None
        modifier_held = False

def on_move(x, y):
    global anchor_pos, accumulator, modifier_held
    
    # 1. Safety check
    if anchor_pos is None or not modifier_held:
        return

    # 2. Prevent infinite loop from the cursor reset
    if (x, y) == anchor_pos:
        return

    # 3. Calculate movement
    dy = y - anchor_pos[1]
    accumulator += dy

    # 4. Snap Cursor Back (Lock position)
    m.position = anchor_pos

    # 5. Scroll Logic
    if abs(accumulator) >= SENSITIVITY:
        steps = int(accumulator / SENSITIVITY)
        
        # NOTE: We are sending a scroll event WHILE Alt is held.
        # Most apps handle this fine, but some might see "Alt+Scroll"
        m.scroll(0, -steps)
        
        accumulator -= (steps * SENSITIVITY)

# Start listeners
with keyboard.Listener(on_press=on_key_press, on_release=on_key_release) as k_listener, \
     mouse.Listener(on_move=on_move) as m_listener:
    k_listener.join()
    m_listener.join()