Get canvas size and draw rectangle in Kivy

I would like to draw something in canvas from .py by using class 'BotRightCanvas'. The initial widgets are all defined in .kv

Problem is when I finally declare BotRightCanvas in .kv, the size of the canvas widget is not coming proper (still 100x100). I would like the green rectangle to coincide with the cyan one.

Here's .py

from kivy.graphics import Color
from kivy.graphics.vertex_instructions import Line, Rectangle, Ellipse
from kivy.metrics import dp
from kivy.uix.widget import Widget
from kivy.uix.boxlayout import BoxLayout
from kivy.core.window import Window


class TestOut(BoxLayout):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def getSize(self, id):
        cSize = id.size
        print('win ' + str(Window.size))
        print('canvas ' + str(id.size))
        print('cSize ' + str(cSize))


class BotRightCanvas(Widget):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        with self.canvas:
            Color(0, 1, 0, 1)
            Line(circle=(self.width / 2, self.height / 2, 25), width=2)
            Line(rectangle=(0, 0, self.width, self.height), width=5)


class PlaygroundApp(App):
    title = "blabla"

    def build(self):
        return TestOut()


if __name__ == "__main__":
    PlaygroundApp().run()

and .kv

<TestOut>:

    BoxLayout:
        orientation: 'vertical'
        Button:
            text:'A'
            height: dp(100)
            size_hint: 1, None
        BoxLayout:
            Button:
                text:'B'
                width: dp(150)
                size_hint: None, 1
            RelativeLayout:
                id: rel_lo
                on_size: root.getSize(rel_lo)
                Widget:
                    canvas:
                        Line:
                            rectangle: (0,0, self.width, self.height)
                            width: 2
                    canvas.before:
                        Color:
                            rgba: 0,1,1,1
                    BotRightCanvas:

I tried printing the final canvas shape in console, seems it initializes with size of 0x0 but later on gets correct size 650x500.

The console output

canvas [0.0, 0]
cSize [0.0, 0]
win (800, 600)
canvas [650.0, 500.0]
cSize [650.0, 500.0]

Any help? Thanks !!

EDIT: Would like to control canvas items from .py

Solution

from kivy.graphics import Color

from kivy.graphics.vertex_instructions import Line, Rectangle, Ellipse

from kivy.metrics import dp

from kivy.uix.widget import Widget

from kivy.uix.boxlayout import BoxLayout

from kivy.core.window import Window

from kivy.lang.builder import Builder

from kivy.app import App

class TestOut(BoxLayout):



    def __init__(self, **kwargs):

        super().__init__(**kwargs)



    def getSize(self, id):

        cSize = id.size

        print('win ' + str(Window.size))

        print('canvas ' + str(id.size))

        print('cSize ' + str(cSize))





class BotRightCanvas(Widget):

    pass

        







Builder.load_string(



    '''

<BotRightCanvas>:

    canvas:

        Color:

            rgba:0, 1, 0, 1

        Line:

            circle:self.width / 2, self.height / 2, 25

            width:2



        Line:

            rectangle:0, 0, self.width, self.height

            width:5

<TestOut>:



    BoxLayout:

        orientation: 'vertical'

        Button:

            text:'A'

            height: dp(100)

            size_hint: 1, None

        BoxLayout:

            Button:

                text:'B'

                width: dp(150)

                size_hint: None, 1

            RelativeLayout:

                id: rel_lo

                on_size: root.getSize(rel_lo)

                Widget:

                    canvas:

                        Line:

                            rectangle: (0,0, self.width, self.height)

                            width: 2

                    canvas.before:

                        Color:

                            rgba: 0,1,1,1

                    BotRightCanvas:

                        size:rel_lo.size

    

    

    '''





)

class PlaygroundApp(App):

    title = "blabla"



    def build(self):

        return TestOut()



for line in open('2.py').readlines():

    print('    '+line)

if __name__ == "__main__":

    PlaygroundApp().run()