app.coffee

mouse_draw = (e) ->
  position = find_position(@)
  e._x = e.clientX - position.x
  e._y = e.clientY - position.y
  $('#x').text(e._x)
  $('#y').text(e._y)
  if currentTool() == 'eraser'
    $('#drawing').hide()
  func = Narwhal.tools[currentTool()][e.type]
  if func?
    func(e)

$ -> 
  $("#drawing").bind('mousedown mousemove mouseup', mouse_draw)

tools.coffee

Narwhal.tools.pencil =
  started: false
  shape: null
  mousedown: (e) ->
    $("#drawing").draw((ctx) ->
      ctx.beginPath()
      ctx.strokeStyle = "#000"
      ctx.lineWidth = Narwhal.global_width
      ctx.lineCap = 'round'
      ctx.moveTo(e._x, e._y)
    )
    @started = true
    @shape = new Narwhal.Squiggle({x: e._x, y: e._y})
    return
  mousemove: (e) ->
    if @started
      @shape.addPoints({x: e._x, y: e._y})
      $("#drawing").draw((ctx) ->
        ctx.lineTo(e._x, e._y)
        ctx.stroke()
      )

  mouseup: (e) ->
    if @started
      @started = false