theta = 0
rotation = 0.1

def setup():
    size(300, 300)
    background(255)

def draw():
    global theta
    translate(width / 2.0, height / 2.0)
    x = theta * cos(theta / PI)
    y = theta * sin(theta / PI)
    point(x, y)
    theta = theta + rotation
    # check restart
    if x > width / 2.0:
        background(255)
        theta = 0