shortline.py

from math import cos, sin

from kivy.uix.widget import Widget
from kivy.graphics import Line
from kivy.clock import Clock
from kivy.app import App
from kivy.properties import ListProperty, NumericProperty


class ShortLineApp(App):
    time = NumericProperty()

    def build(self):
        Clock.schedule_interval(self.update, 0)
        widget = Widget()
        with widget.canvas:
            widget.line = Line(points=[], width=4)
        return widget

    def update(self, dt):
        self.time += dt
        point = (
            self.root.center_x + self.root.width / 2 * cos(self.time),
            self.root.center_y + self.root.height / 2 * sin(self.time)
        )

        line = self.root.line
        line.points += point
        if len(line.points) > 200:
            line.points.pop(0)
            line.points.pop(0)


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