Hammerspoon/Lua script to enable 2d scrolling on key(CTRL) press

gistfile1.txt

-- SCROLL ON MOUSE MOVEMENT WHEN CTRL BUTTON DOWN
-- inspired by 
-- https://superuser.com/questions/303424/can-i-enable-scrolling-with-middle-button-drag-in-os-x
--
-- add to hammerspoon config and hit hs.reload()

local scrollModifier = "ctrl"
local oldMousePosition = {}
local scrollIntensity = 4

ctrlDownMouseTracker = hs.eventtap.new({ hs.eventtap.event.types.mouseMoved }, function(e)
    oldMousePosition = hs.mouse.getAbsolutePosition()    

    local dX = e:getProperty(hs.eventtap.event.properties['mouseEventDeltaX'])
    local dY = e:getProperty(hs.eventtap.event.properties['mouseEventDeltaY'])

    hs.eventtap.scrollWheel({dX * scrollIntensity , dY * scrollIntensity }, {})
    -- put the mouse back
    hs.mouse.setAbsolutePosition(oldMousePosition)
end)

dragCtrlToScroll = hs.eventtap.new({ hs.eventtap.event.types.flagsChanged }, function(e)
    local modifiers = e:getFlags()
    if ( modifiers[ scrollModifier ] ) 
        then 
            ctrlDownMouseTracker:start()
        else
            ctrlDownMouseTracker:stop()
        end
end)
dragCtrlToScroll:start()

Using it on mac with external keyboard that has built in trackball. Not the same as trackpad, but creates reasonable emulation of scroll experience.