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

#放物線
def f(x):
    y = x**2
    return y

#コメントの挿入
def interlude(imgs,ax,text,frames):
    
    fdic = {"ha" : "center",
            "va" : "center",
            "size" : 20,
            "color" : "white",
            "fontfamily": "Meiryo",
            }

    
    boxdic = {"facecolor" : "black",
              "pad" : 300,
              }
    
    for i in range(frames):
        interlude=ax.text(0,1,text,
                          fontdict=fdic,bbox=boxdic)
        imgs.append([interlude])

#十字マークをプロット
def plot_xmark(ax,x):
    slope = 2*x
    rad   = np.arctan(slope)
    deg   = np.rad2deg(rad)
    P = ax.plot(x,f(x),marker=(4,2,deg),
                color="r",markersize=20,markeredgewidth=4)
    return P

#図の準備
fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_xlim(-2,2)
ax.set_ylim(-1,3)
ax.axhline(0,color='0.6')
ax.plot(2,0,marker=5,color='0.6')
ax.axvline(0,color='0.6')
ax.plot(0,3,marker=6,color='0.6')
ax.set_aspect("equal")
ax.axis("off")
ax.set_title("2020京大数学　文系第２問",pad=15)

x = np.arange(-2,2.05,0.05)
y = x**2
ax.plot(x,y,color="0.3",linewidth=4)

#変数の準備
A = np.arange(0.1,np.sqrt(3),0.05)
B = np.arange(-2*np.sqrt(3),2*np.sqrt(3),0.2)

imgs = []

#１つ目のパターン
for a in A:
    
    y1 = -1/(4*a**2)*x**2 + a**2 + 1/4
    C1 = ax.plot(x,y1,color="0.3",linewidth=4)
    
    P1 = plot_xmark(ax,-a)
    P2 = plot_xmark(ax, a)
    
    imgs.append(C1+P1+P2)

comment='''\
えっ　(;ﾟдﾟ)

これだけじゃないの？？'''
interlude(imgs,ax,comment,20)

#２つ目のパターン
for b in B:
    
    y2 = -x**2 + b*x + 1/2
    C2 = ax.plot(x,y2,color="0.3",linewidth=4)
    
    alpha1 = (b+np.sqrt(b**2+4))/4
    alpha2 = (b-np.sqrt(b**2+4))/4
    
    P1 = plot_xmark(ax,alpha1)
    P2 = plot_xmark(ax,alpha2)
    
    imgs.append(C2+P1+P2)

comment='''\
そのパターンもあるのネ

(；´Д｀)　ﾄﾎﾎ'''    
interlude(imgs,ax,comment,20)

mov=ani.ArtistAnimation(fig, imgs, 100)
plt.show()