import numpy
import matplotlib.pyplot as plt
from matplotlib import animation

N_CIRCLES = 20
N_FRAMES = 150

T_CIRCLES = numpy.linspace(0,10,N_CIRCLES)
T = numpy.linspace(0,10,N_FRAMES)

fig = plt.figure(figsize=(3,3), dpi=100)
ax = plt.axes(xlim=(-5,10), ylim=(-7.5,7.5))

emitter = plt.Circle((0,0),.3,color='k', )
ax.add_patch(emitter)


observer = plt.Circle((7,-2),.3,color='k', )
ax.add_patch(observer)

def position(t):
    return 2*t

plt.axis('off')
circles = []
for t_i in range(N_CIRCLES):
    color='k'
    if (t_i==0):
        color = 'r'
    elif (t_i==1):
        color = 'b'
    circles.append(plt.Circle((position(T_CIRCLES[t_i]),0),0,color=color, fill=False))
    ax.add_patch(circles[-1])

def func(nframe):
    print nframe
    emitter.center = (position(T[nframe]), 0)
    for t_i in range(N_CIRCLES):
        circles[t_i].radius = max(0,T[nframe]-T_CIRCLES[t_i])
    return circles[0], circles[1],

ani = animation.FuncAnimation(fig, func, N_FRAMES)
ani.save('plotcircles.gif', writer='imagemagick', fps=25, dpi=100)

#plt.show()