import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as ani
import matplotlib.patches as patches

#座標の準備
fig = plt.figure()
fig.suptitle("2006京大数学　理系第５問",x=0.96,y=0.96,
             color="0.7",ha="right")
ax = fig.add_subplot(111)
ax.axis("off")
ax.set_aspect("equal")

#三角形たちを準備
a=np.array([2/3,3/4])
b=np.array([1,0])
c=np.array([0,0])
ABC = patches.Polygon(xy=[a,b,c],fill=False,ec="0.7",
                      linewidth=4,joinstyle="round")
ax.add_patch(ABC)
PQR = patches.Polygon(xy=[a,a,c],fc="palegoldenrod",
                      alpha=0.7,zorder=-20)
ax.add_patch(PQR)
l1,l2,l3 = ax.plot([],[],[],[],[],[],
                   color="w",lw=0.8,zorder=-10)

#軌跡の準備
trajectory,= ax.plot([],[],"steelblue",lw=7,alpha=0.4)
G,= ax.plot([],[],"slategrey",marker="o",markersize=7)

#イージング関数
def easing(x):
    if x<0.5:
        return 2*x**2
    else:
        return 1-(-2*x+2)**2/2

#ぬりぬりする関数
def nurinuri(i,p1,p2,p3): 
    p = p1
    k = i/199
    q = (1-k)*p1+k*p2
    k = np.sin(25*k*np.pi/2)**2
    r = (1-k)*p3+k*p2
    PQR.set_xy([p,q,r])
    
    l1.set_data(zip(p,(q+r)/2))
    l2.set_data(zip(q,(r+p)/2))
    l3.set_data(zip(r,(p+q)/2))
    
    g = (p+q+r)/3
    G.set_data([g[0]],[g[1]])
    tx = np.append(trajectory.get_data()[0],g[0])
    ty = np.append(trajectory.get_data()[1],g[1])
    trajectory.set_data(tx,ty)

#上演
def update(i):
    if i<200:
        nurinuri(i,a,b,c)
    elif i<400:
        nurinuri(i-200,b,c,a)
    elif i<600:
        nurinuri(i-400,c,a,b)
    elif i<630:
        alpha = 1-(i-600)/29
        G.set_alpha(alpha)
    
mov = ani.FuncAnimation(fig,update,660,interval=100)
plt.show()