from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Line

class DrawInput(Widget):
    
    def on_touch_down(self, touch):
        print(touch)
        with self.canvas:
            touch.ud["line"] = Line(points=(touch.x, touch.y))
        
    def on_touch_move(self, touch):
        print(touch)
        touch.ud["line"].points += (touch.x, touch.y)
		
    def on_touch_up(self, touch):
        print("RELEASED!",touch)


class SimpleKivy4(App):
    
    def build(self):
        return DrawInput()

if __name__ == "__main__":
    SimpleKivy4().run()
		

Here, we're first importing a new aspect from Kivy, Line. This is so we can draw a line.

Now, we modify our on_touch_down to, using the canvas, which is part of our inherited Widget, we're going to start defining our line as a Line element, where the points are just one point for now, which is the x,y coordinates of our touch_down.

Next, we modify our on_touch_move method to modify our touch.ud["line"] by appending the new touch.x and touch.y coordinates, so now we have more coordinates, drawing a line using them.

Finally, we modify the SimpleKivy4 root app to return our new DrawInput class, which will now give us an app that allows us to draw!