hammerspoon_marble_trackball_scroll.lua

-- Source:https://github.com/owenlo/Marble-Hammerspoon
-- Source:https://github.com/tekezo/Karabiner/issues/814#issuecomment-415388742
-- Source:https://gist.github.com/ParatechX/c03c1146f7cd719dbfd65a337c7228f3

-- HANDLE SCROLLING WITH MOUSE BUTTON PRESSED
local backMouseButton = 3
local forwardMouseButton = 4
local deferred = false
local VSCODE = 'Code'
local VIM = 'MacVim'

function setOverrides(e)
    overrideOtherMouseDown:stop()
    overrideOtherMouseUp:stop()
    hs.eventtap.otherClick(e:location(), 0, pressedMouseButton)
    overrideOtherMouseDown:start()
    overrideOtherMouseUp:start()	
end

overrideOtherMouseDown = hs.eventtap.new({ hs.eventtap.event.types.otherMouseDown }, function(e)
    -- print("down")    
    local pressedMouseButton = e:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber'])
    if backMouseButton == pressedMouseButton or forwardMouseButton == pressedMouseButton then
        deferred = true
        return true
    end
end)

overrideOtherMouseUp = hs.eventtap.new({ hs.eventtap.event.types.otherMouseUp }, function(e)
    -- print("up")
    local pressedMouseButton = e:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber'])
    local appName = hs.application.frontmostApplication():name()

    if backMouseButton == pressedMouseButton then 
        if (deferred) then
            setOverrides(e)
            if appName == VSCODE then
                hs.eventtap.keyStroke({"ctrl"}, "-")
            elseif appName == VIM then

            else
                hs.eventtap.keyStroke({"cmd"}, "[")
            end
            return true
        end
        return false
    end

    if forwardMouseButton == pressedMouseButton then 
        if (deferred) then
            setOverrides(e)
            if appName == VSCODE then
                hs.eventtap.keyStroke({"ctrl", "shift"}, "-")
            elseif appName == VIM then
            else
                hs.eventtap.keyStroke({"cmd"}, "]")
            end
            return true
        end
        return false
    end
    return false
end)

local scrollModifier = "ctrl"
local oldMousePosition = {}
local scrollIntensityOther = -4	-- negative multiplier makes mouse work like traditional scrollwheel
local scrollIntensityCtrl = -4	-- negative multiplier makes mouse work like traditional scrollwheel

dragOtherToScroll = hs.eventtap.new({ hs.eventtap.event.types.otherMouseDragged }, function(e)
    local pressedMouseButton = e:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber'])
    -- print ("pressed mouse " .. pressedMouseButton)
    if backMouseButton == pressedMouseButton or forwardMouseButton == pressedMouseButton then 
        -- print("scroll");
        deferred = false

        oldMousePosition = hs.mouse.absolutePosition()    
        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 * scrollIntensityOther, dy * scrollIntensityOther}, {}, 'pixel')
        -- put the mouse back
        hs.mouse.absolutePosition(oldMousePosition)

        return true, {scroll}
    else 

        return false, {}
    end 
end)

-- Ctrl Mouse Tracker

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'])

    -- print("ctrlDownMouseTracker runs dx=" .. dx .. " dy=" .. dy)

    hs.eventtap.scrollWheel({dx * scrollIntensityCtrl , dy * scrollIntensityCtrl }, {}, 'pixel')
    -- 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)

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