init.lua

hotkey.bind({"command", "option"}, 'down', function()
  local resizing = hs.hotkey.modal.new()
  local activeWindow = hs.window.focusedWindow()
  local backdrop = hs.drawing.rectangle( hs.screen.mainScreen():frame() )
    :setFillColor({ red=0, green=0, blue=0, alpha=0.2 })
  local resizeIndicator = hs.drawing.rectangle({ x=0, y=0, w=0, h=0 })
    :setFillColor({ red=1, green=1, blue=1, alpha=0.3 })
    :setStrokeWidth(1)
    :setStroke(1)
    :setStrokeColor({ red=1, green=1, blue=1, alpha=0.5 })
  local startPosition = nil
  local movePosition = nil
  local followMouse = hs.eventtap.new({ hs.eventtap.event.types.leftMouseDragged }, function()
    currentPosition = hs.mouse.getRelativePosition()
    if movePosition  then
      -- resizeIndicator.setTopLeft
      resizeIndicator
        :setTopLeft({
          x= (startPosition.x + currentPosition.x) - movePosition.x,
          y= (startPosition.y + currentPosition.y) - movePosition.y,
        })
    else
      resizeIndicator
        :setTopLeft({
          x= math.min(startPosition.x, currentPosition.x),
          y= math.min(startPosition.y, currentPosition.y),
        })
        :setSize({
          w= math.max(startPosition.x - currentPosition.x, currentPosition.x - startPosition.x),
          h= math.max(startPosition.y - currentPosition.y, currentPosition.y - startPosition.y),
        })
    end
  end)

  function resizing.entered()
    backdrop
      :bringToFront(true)
      :show()
    resizeIndicator
      :bringToFront(true)
  end

  function resizing:exited()
    followMouse:stop()
    backdrop:delete()
    resizeIndicator:delete()
    activeWindow:focus()
  end

  resizing:bind({}, 'escape', function() resizing:exit() end)
  resizing:bind({}, 'space',
    function() movePosition = hs.mouse.getRelativePosition() end,
    function()
      movePosition = nil
      startPosition = resizeIndicator:frame()
    end
  )

  backdrop:setClickCallback(function()
    pcall(function() activeWindow:setFrame( resizeIndicator:frame() ) end)
    resizing:exit()
  end, function()
    startPosition = hs.mouse.getRelativePosition()
    resizeIndicator
      :setTopLeft( startPosition )
      :setSize({ w=1, h=1 })
      :show()
    followMouse:start()
  end)

  resizing:enter()

end)