from kivy.app import runTouchApp
from kivy.lang import Builder
runTouchApp(Builder.load_string("""
Screen:
    name: 'CameraScreen'
    StackLayout:
        ActionBar:
            background_color: [1,1,1,0]
            ActionView:
                use_separator: True
                ActionPrevious:
                    app_icon: 'resources/img/appbar.home.png'
                    with_previous: True
                    on_release: app.home()

        RelativeLayout:
            id: rl
            Widget:
                id: preview
                size_hint: None, None
                size: 112,112
                pos_hint: {'center_x': 0.5, 'center_y': 0.5}
                canvas:
                    Color:
                        rgba: 1,1,0,1
                    Rectangle:
                        pos: rl.pos
                        size: rl.size
"""))