square_orbit.pyde

def draw_square(cx, cy, r, l, theta):
    pushMatrix()
    quarter_turns, theta = divmod(theta, HALF_PI)
    translate(cx, cy)
    rotate(quarter_turns * HALF_PI)
    critical_theta = atan(l * 1.0 / (2 * r + l))
    if theta <= critical_theta:
        x = r + l / 2.0
        y = (r + l / 2.0) * tan(theta)
    elif theta >= HALF_PI - critical_theta:
        x = (r + l / 2.0) / tan(theta)
        y = r + l / 2.0
    else:
        a = 1
        b = -l * (cos(theta) + sin(theta))
        c = l ** 2 / 2.0 - r ** 2
        R = (-b + sqrt(b ** 2 - 4 * a * c)) / (2 * a)
        x = R * cos(theta)
        y = R * sin(theta)
    rect(x, y, l, l)
    line(0, 0, x, y)
    popMatrix()

def setup():
    global theta
    size(800, 800)
    theta = 0.0

THETA_RATE = 0.01

def draw():
    global theta
    theta += THETA_RATE
    background(0)
    stroke(255)
    noFill()
    ellipseMode(RADIUS)
    rectMode(CENTER)
    ellipse(400, 400, 200, 200)
    draw_square(400, 400, 200, 100, theta)