Add middle-button panning support to Sketch to match Figma, Fusion 360, etc.

hammerspoon.lua

-- Make Sketch use the middle mouse button for dragging like Figma, Fusion 360, etc.
local middleMouseDown = false

-- Function to handle the middle mouse down event
local function middleMouseDownHandler(event)
    if event:getType() == hs.eventtap.event.types.otherMouseDown then
        if event:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber']) == 2 then
            middleMouseDown = true
            -- Simulate holding down the space bar
            hs.eventtap.event.newKeyEvent(hs.keycodes.map['space'], true):post()
            -- Simulate a left mouse button down at the current mouse location
            hs.eventtap.event.newMouseEvent(hs.eventtap.event.types.leftMouseDown, event:location()):post()
            return true -- prevent the event from passing through
        end
    end
    return false
end

-- Function to handle the middle mouse up event
local function middleMouseUpHandler(event)
    if event:getType() == hs.eventtap.event.types.otherMouseUp then
        if event:getProperty(hs.eventtap.event.properties['mouseEventButtonNumber']) == 2 then
            middleMouseDown = false
            -- Simulate releasing the space bar
            hs.eventtap.event.newKeyEvent(hs.keycodes.map['space'], false):post()
            -- Simulate a left mouse button up at the current mouse location
            hs.eventtap.event.newMouseEvent(hs.eventtap.event.types.leftMouseUp, event:location()):post()
            return true -- prevent the event from passing through
        end
    end
    return false
end

-- Function to handle mouse dragging while middle mouse button is held
local function mouseDragHandler(event)
    if middleMouseDown then
        -- Simulate dragging with the left mouse button at the updated location
        hs.eventtap.event.newMouseEvent(hs.eventtap.event.types.leftMouseDragged, event:location()):post()
        return true -- prevent the event from passing through
    end
    return false
end

-- Create an eventtap watcher for the middle mouse down, up, and drag events
local middleMouseWatcher = hs.eventtap.new({hs.eventtap.event.types.otherMouseDown, hs.eventtap.event.types.otherMouseUp, hs.eventtap.event.types.otherMouseDragged}, function(event)
    local sketchApp = hs.application.find("com.bohemiancoding.sketch3")
    
    if sketchApp == nil then 
        return false
    end

    --- If not the frontmost app, do nothing
    if sketchApp:isFrontmost() then
        if middleMouseDownHandler(event) or middleMouseUpHandler(event) or mouseDragHandler(event) then
            return true
        else
            return false
        end
    else
        return false
    end
end)

-- Start the watcher
middleMouseWatcher:start()