Scroll with auxiliary mouse buttons on wayland

side-button-scroll.sh

#!/bin/bash

# This file need to be executed with root privilegies

# Dependencies:
# - evemu
# - xinput


MOUSE_ID=6 #Get the correct id with xinput list

# First we'll remap the side buttons to mouse-wheel and disable the mouse-wheel.
# The default mouse-wheel buttons are 4 and 5, so we remap 4 and 5 to 0, to disable it
# The side buttons on my mouse are 8 and 9, so we remap those to 5 and 4
# After this command alone you should be able to scroll with the extra mouse buttons.
# But you'd need one click per line-scroll
# Very hard to use it like that.

# DISCLAIMER: On your mouse the extra buttons may been mapped to other values than 8 and 9.
# Test them with xinput --query-state $MOUSE_ID

xinput set-button-map $MOUSE_ID 1 2 3 0 0 6 7 5 4 10 

# The following while loop allow us to be able to keep scrolling while the button is hold down
while true; do
   
    STATE1=$(xinput --query-state $MOUSE_ID | grep "button\[9" | sort); #9 and 8 are the button codes, if you run query state and press the button you'll know what button to call.
   
    STATE2=$(xinput --query-state $MOUSE_ID | grep "button\[8" | sort);
    

    if [ $STATE1 == "button[9]=up" ] && [ $STATE2 == "button[8]=up" ]; then
      SCROLL="NONE"
    fi
    
    if [ $STATE1 == "button[9]=down" ] && [ $SCROLL != "UP" ]; then
      SCROLL="DOWN"
      # Wayland doesn't support xdotool so we need to use evemu-event. 
      # You can use sudo evemu-record /dev/input/event3 > recording.evemu to record your events
      # Then you can see the content of recording.evemu to check the event type, code and value
      # the lines will look somethhing like this:
      # E: 3.018057 0001 0113 0001	# EV_KEY / BTN_SIDE             1
      # E: 3.018057 0001 0113 0001	# EV_KEY / BTN_SIDE             0
      # Usually when you click a mouse button it will fire an event with value 1 for when the button goes down
      # And another event with value 0 saying the button was released
      # Here we want to simulate many complete clicks, that's why we need to fire two events.
      evemu-event /dev/input/event3 --type EV_KEY --code BTN_SIDE --value 1 --sync
      evemu-event /dev/input/event3 --type EV_KEY --code BTN_SIDE --value 0 --sync
    fi
    
    if [ $STATE2 == "button[8]=down" ] && [ $SCROLL != "DOWN" ]; then
      SCROLL="UP"
      evemu-event /dev/input/event3 --type EV_KEY --code BTN_EXTRA --value 1 --sync
      evemu-event /dev/input/event3 --type EV_KEY --code BTN_EXTRA --value 0 --sync
    fi

    sleep .01 # If you increase the time the scroll will be slower, if you reduce it will be faster.
done

This script was made and tested on:
Fedora 32 using Wayland
Mouse: GXT 922 Gaming Mouse

I don't know exactly why but this works on every window but terminal and gedit, I think those still rely on Xorg or something like that internally, but since I don't use those much, isn't a problem to me.