如何在Kivy中释放按钮时生成随机颜色的随机2D几何图形？

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.graphics import Color, Ellipse, Rectangle
from random import random

class MyWidget(Widget):
    def on_touch_up(self, touch):
        if self.collide_point(*touch.pos):
            with self.canvas:
                # 生成随机颜色
                color = (random(), random(), random(), 1)
                Color(*color)
                
                # 生成随机2D几何图形
                shape = random()
                if shape < 0.5:
                    # 生成随机椭圆
                    size = (50, 50)
                    pos = (touch.x - size[0]/2, touch.y - size[1]/2)
                    Ellipse(pos=pos, size=size)
                else:
                    # 生成随机矩形
                    size = (50, 50)
                    pos = (touch.x - size[0]/2, touch.y - size[1]/2)
                    Rectangle(pos=pos, size=size)

class MyApp(App):
    def build(self):
        return MyWidget()

if __name__ == '__main__':
    MyApp().run()