gistfile1.txt

# Class definition of ChannelImageButton
from kivy.graphics import Clear, Rectangle, Color
from kivy.properties import ListProperty

class ChannelImageButton( ButtonBehavior, Image ):
      losses = ListProperty()
      gains = ListProperty()
      
      def __init__(self, **kwargs):
          super(ChannelImageButton, self).__init__(**kwargs)
          self.bind(pos=self.update_canvas, size=self.update_canvas, losses=update_canvas, gains=update_canvas)
          
      def update_canvas(self, *args):
          with self.canvas.after:
            Clear()
            for i in self.losses:
                  Color(1, 0, 0, .25)
                  Rectangle(pos=(i[0], 0 ),
                            size=(i[1] - i[0], self.height))
            for i in self.gains:
                  Color(0, 1, 0, 0.25)
                  Rectangle(pos=(i[0], 0),
                              size=(i[1] - i[0], self.height))
            
      

# Code that is adding the ChannelImageButtons to the GridLayout in the ScrollView.

                # Get a list of images
                channels = project.get_image_channels( btn.__image_id__ )
                # Clear any widgets in the GridLayout in the ScrollView
                self.channel_scroll_view.button_list.clear_widgets( )

                # Create ChannelImageButtons, and set their texture to the image
                # Try to draw a rectangle on the buttons canvas
                for i in channels:
                        image = CoreImage( io.BytesIO( i[ 1 ] ), ext = "jpg" )

                        losses = project.get_channel_loss( i[ 0 ] )
                        gains  = project.get_channel_gain( i[ 0 ] )

                        btn = ChannelImageButton(losses=losses, gains=gains)
                        btn.__channel_id__ = i[0]
                        btn.texture = image.texture
                        self.channel_scroll_view.button_list.add_widget(btn)                        
kv file:

<ChannelImageButton>:
   size_hint: None, None
   size: self.texture_size
     
<ChannelScrollView>:
        button_list: button_list
        size_hint_x: None
        width: self.minimum_width

        canvas.before:
                Color:
                        rgba: hex( "#646668" )
                Rectangle:
                        pos: self.pos
                        size: self.size

        GridLayout:
                canvas.before:
                        Color:
                                rgba: ( 1, 1, 1, 1 )
                        Rectangle:
                                pos: self.pos
                                size: self.size
                id: button_list
                size_hint_y: None
                size_hint_x: None
                spacing: 50
                cols: 1
                size: self.minimum_size