hammerspoon-mouse.lua

-- HANDLE SCROLLING
-- positive multiplier (== natural scrolling) makes mouse work like traditional scrollwheel
local scrollmult = -4

-- mouselog = hs.eventtap.new({'all'}, function(e)
--   print("event " .. e:getType())
-- end)
-- mouselog:start()

-- The were all events logged, when using `{"all"}`
mousetap = hs.eventtap.new({25,26,27}, function(e)
  local oldmousepos = hs.mouse.getAbsolutePosition()
  local pressedMouseButton = e:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber'])

  -- print("event " .. e:getType() .. " mousebutton " .. pressedMouseButton)

  -- If OSX button 4 is pressed, allow scrolling
  if pressedMouseButton == 3 then
    local dx = e:getProperty(hs.eventtap.event.properties['mouseEventDeltaX'])
    local dy = e:getProperty(hs.eventtap.event.properties['mouseEventDeltaY'])

    local scroll = hs.eventtap.event.newScrollEvent({dx * scrollmult, dy * scrollmult}, {}, 'pixel')

    -- put the mouse back
    hs.mouse.setAbsolutePosition(oldmousepos)
    
    return true, {scroll}
  else
    return false, {}
  end
end)
mousetap:start()