应用matplotlib.animation.FuncAnimation绘制摆线

上次尝试了用matplotlib.animation.ArtistAnimation绘制摆线，实际上也可以用matplotlib.animation.FuncAnimation实现同样的功能。

导入相关文件

引用的库包括numpy，matplotlib，代码如下：

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

配置ffmpeg和imagemagick

动图会保存为.gif和.mp4两种格式，需要用到这两个库

# Config the ffmpeg_path
plt.rcParams['animation.ffmpeg_path'] = r'D:\Data\software\programming\ffmpeg\ffmpeg-7.0.1-full_build\bin\ffmpeg.exe'
# Config the ImageMagick path with convert_path
plt.rcParams['animation.convert_path'] = r'D:\Data\software\programming\ImageMagick\ImageMagick-7.1.1-33-portable-Q16-HDRI-x64\convert.exe'

animation.FuncAnimation介绍

通过以下命令，可以查看这个方法：

可见，该方法第一个参数是绘图句柄fig，第二个参数是绘制函数func，第三个参数是像素帧frames。

animation.FuncAnimation?

Init signature:
animation.FuncAnimation(
fig,
func,
frames=None,
init_func=None,
fargs=None,
save_count=None,
*,
cache_frame_data=True,
**kwargs,
)
Docstring:
TimedAnimation subclass that makes an animation by repeatedly calling
a function func.

… note::

You must store the created Animation in a variable that lives as long
as the animation should run. Otherwise, the Animation object will be
garbage-collected and the animation stops.

Parameters

fig : ~matplotlib.figure.Figure
…
Whether frame data is cached. Disabling cache might be helpful when
frames contain large objects.
File: d:\miniconda3\lib\site-packages\matplotlib\animation.py
Type: type
Subclasses:
Output is truncated. View as a scrollable element or open in a text editor. Adjust cell output settings…

animation.FuncAnimation??

Init signature:
animation.FuncAnimation(
fig,
func,
frames=None,
init_func=None,
fargs=None,
save_count=None,
*,
cache_frame_data=True,
**kwargs,
)
Source:
class FuncAnimation(TimedAnimation):
“””
TimedAnimation subclass that makes an animation by repeatedly calling
a function func.

.. note::

    You must store the created Animation in a variable that lives as long
    as the animation should run. Otherwise, the Animation object will be
    garbage-collected and the animation stops.

Parameters

…

save_count = _api.deprecate_privatize_attribute("3.7")

File: d:\miniconda3\lib\site-packages\matplotlib\animation.py
Type: type
Subclasses:
Output is truncated. View as a scrollable element or open in a text editor. Adjust cell output settings…

定义圆及像素帧方法

• 设置圆的半径

# 圆半径
R = 1

• 定义圆和像素帧（摆线定义）

def circle(a, b, r, num=100):
    # (a,b): 圆心坐标
    # r: 圆半径
    # num: 采样密度，默认100
    x, y = [0]*num, [0]*num
    for i,theta in enumerate(np.linspace(0,2*np.pi,num)):
        x[i] = a + r*np.cos(theta)
        y[i] = b + r*np.sin(theta)
    return x, y

# 摆线定义
def gen():
    for theta in np.linspace(0,4*np.pi,100):
        yield R*(theta-np.sin(theta)), R*(1-np.cos(theta)), R*theta   

绘制图像

配置图像属性，并为动画绘制作准备。

fig = plt.figure(figsize=(6,3))
ax = fig.add_subplot(111)
ax.set_ylim(0, 3)
ax.set_xlim(0, 15)
ax.set_xlabel('x')
ax.set_ylabel('y')
ax.set_aspect('equal')
ax.grid()
time_text = ax.text(0.05, 0.8, '', transform=ax.transAxes)

cycloid, = ax.plot([], [], 'r-', lw=2)
line, = ax.plot([], [], 'y-', lw=2)
circle_line, = ax.plot([], [], 'g', lw=2)
point, = ax.plot([], [], 'bo', ms=4)

xx, yy = [], []
def func(data):
    x, y, Rt = data
    time_text.set_text(r'$	heta$ = %.2f $\pi$' % (Rt/np.pi))
    xx.append(x)
    yy.append(y)
    cx, cy = circle(Rt, R, R)
    
    cycloid.set_data(xx, yy)
    line.set_data((x,Rt), (y,R))
    circle_line.set_data(cx, cy)
    point.set_data([x], [y])   

创建动画

ani = animation.FuncAnimation(fig, func, frames=gen, blit=False, save_count=100, interval=50)

保存为mp4和gif格式

fn = 'cycloid_FuncAnimation_blog'
ani.save('%s.mp4'%(fn), writer='ffmpeg', fps=1000/50)
xx, yy = [], [] # 清空轨迹缓存
ani.save('%s.gif'%(fn), writer='imagemagick', fps=1000/50)

在Jupyter Notebook上显示动画

plt.rcParams['animation.html'] = 'html5'
xx, yy = [], []
ani