title: Kivy have a clickable button on a canvas draw
body: <p>I am trying to have people draw a clock and when they are done to click the submit button and it will take a screenshot. When I use the canvas to draw I can not use the button anymore.</p>
  
  <p>Is there a way to place the button on top of the canvas so that it is still clickable?</p>
  
  <p>main.py</p>
  
  <pre><code>class Clock(Screen):
      def on_touch_down(self, touch):
          print(touch)
          with self.canvas.before:
              touch.ud["line"] = Line(points = (touch.x, touch.y), width = 2)
  
      def on_touch_move(self, touch):
          print(touch)
          touch.ud["line"].points += (touch.x, touch.y)
  
      def on_touch_up(self, touch):
          print("released", touch)
  </code></pre>
  
  <p>clock.kv</p>
  
  <pre><code>#:import utils kivy.utils
  
  &lt;Clock&gt;:
      FloatLayout
          canvas.before:
              Color:
                  rgba: .5, .5, .5, .5
              Line:
                  width: 50
                  rectangle: self.x, self.y, self.width, self.height
  
          Label:
              pos_hint: {"top": .9, "center_x": .5}
              size_hint: 1, .1
              text: "Draw a clock."
              font_size: 25
          BoxLayout:
              id: myexport
          Button:
              pos_hint: {"top": .1, "right": 1}
              size_hint: .1, .1
              text:
                  "Submit"
              on_release:
                  app.change_screen("animals1")
                  myexport.export_to_png("Clock.png")
  </code></pre>