hammerspoon draw box and obtain coordinates

init.lua

hs.hotkey.bind(modShiftHyper, "W", function()
  -- local tracking = false

  local startingMousePosition = hs.mouse.getAbsolutePosition()
  local max = hs.screen.mainScreen():fullFrame()
  local maxCanvas = hs.canvas.new{x=max.x, y=max.y, h=max.h, w=max.w}
  maxCanvas:clickActivating(false)
  maxCanvas:canvasMouseEvents(true, true, false, true)
  maxCanvas:mouseCallback(function(_, event, id, x, y)
    local currentMousePosition = hs.mouse.getAbsolutePosition()
    if event == "mouseMove" then
      -- if tracking then
        maxCanvas:replaceElements({
          type="rectangle",
          action="stroke",
          strokeWidth=2.0,
          strokeColor= {green=1.0},
          frame = {
            x=startingMousePosition.x,
            y=startingMousePosition.y,
            h=(currentMousePosition.y-startingMousePosition.y),
            w=(currentMousePosition.x-startingMousePosition.x)
          },
        })
      -- end
    -- elseif event == "mouseDown" then
      -- tracking=true
    elseif event == "mouseUp" then
      print(hs.inspect(startingMousePosition))
      print(hs.inspect(currentMousePosition))
      maxCanvas:delete()
    end
  end)
  maxCanvas:level("dragging")
  maxCanvas:show()
end)

Thanks for this! I learned some things from it.