Scrolling by trackball with clicking middle button using Hammerspoon

init.lua

-- HANDLE SCROLLING

local deferred = false

overrideOtherMouseDown = hs.eventtap.new({ hs.eventtap.event.types.otherMouseDown }, function(e)
    --print("down"))
    deferred = true
    return true
end)

overrideOtherMouseUp = hs.eventtap.new({ hs.eventtap.event.types.otherMouseUp }, function(e)
    -- print("up"))
    if (deferred) then
        overrideOtherMouseDown:stop()
        overrideOtherMouseUp:stop()
        hs.eventtap.otherClick(e:location())
        overrideOtherMouseDown:start()
        overrideOtherMouseUp:start()
        return true
    end

    return false
end)


local oldmousepos = {}
local scrollmult = -4   -- negative multiplier makes mouse work like traditional scrollwheel
dragOtherToScroll = hs.eventtap.new({ hs.eventtap.event.types.otherMouseDragged }, function(e)
    -- print("scroll");

    deferred = false

    oldmousepos = hs.mouse.getAbsolutePosition()    

    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}
end)

overrideOtherMouseDown:start()
overrideOtherMouseUp:start()
dragOtherToScroll:start()