使用画布的Kivy :如何限制绘画区域？

from kivy.app import App
from kivy.uix.scatter import Scatter
from kivy.uix.label import Label
from kivy.uix.floatlayout import FloatLayout

class DrawingArea(Scatter):
    def __init__(self, **kwargs):
        super(DrawingArea, self).__init__(**kwargs)
        self.do_translation = False  # 禁止平移
        self.do_rotation = False  # 禁止旋转
        self.do_scale = False  # 禁止缩放

        # 添加画布和其他绘图组件
        canvas = self.canvas
        # ...

        # 添加其他绘图组件
        # ...

class MyApp(App):
    def build(self):
        root = FloatLayout()
        drawing_area = DrawingArea()
        root.add_widget(drawing_area)
        return root

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