FuncAnimation#

TheFuncAnimation class allows us to create ananimation by passing a function that iteratively modifies the data of a plot.This is achieved by using thesetter methods on variousArtist (examples:Line2D,PathCollection, etc.). A usualFuncAnimation object takes aFigure that we want to animate and a functionfunc that modifies the data plotted on the figure. It uses theframesparameter to determine the length of the animation. Theinterval parameteris used to determine time in milliseconds between drawing of two frames.Animating usingFuncAnimation typically requires these steps:

1. Plot the initial figure as you would in a static plot. Save all the createdartists, which are returned by the plot functions, in variables so that you canaccess and modify them later in the animation function.

2. Create an animation function that updates the artists for a given frame.Typically, this callsset_* methods of the artists.

3. Create aFuncAnimation, passing theFigure and the animation function.

4. Save or show the animation using one of the following methods:

   • pyplot.show to show the animation in a window

   • Animation.to_html5_video to create a HTML<video> tag

   • Animation.to_jshtml to create HTML code with interactive JavaScript animationcontrols

   • Animation.save to save the animation to a file

The following table shows a few plotting methods, the artists they return and somecommonly usedset_* methods that update the underlying data. While updating datais the most common operation in animations, you can also update other aspects such ascolor or text position.

Covering the set methods for all types of artists is beyond the scope of thistutorial but can be found in their respective documentations. An example ofsuch update methods in use forAxes.scatter andAxes.plot is as follows.

fig,ax=plt.subplots()t=np.linspace(0,3,40)g=-9.81v0=12z=g*t**2/2+v0*tv02=5z2=g*t**2/2+v02*tscat=ax.scatter(t[0],z[0],c="b",s=5,label=f'v0 ={v0} m/s')line2=ax.plot(t[0],z2[0],label=f'v0 ={v02} m/s')[0]ax.set(xlim=(0,3),ylim=(-4,10),xlabel='Time [s]',ylabel='Z [m]')ax.legend()defupdate(frame):# for each frame, update the data stored on each artist.x=t[:frame]y=z[:frame]# update the scatter plot:data=np.stack([x,y]).Tscat.set_offsets(data)# update the line plot:line2.set_xdata(t[:frame])line2.set_ydata(z2[:frame])return(scat,line2)ani=animation.FuncAnimation(fig=fig,func=update,frames=40,interval=30)plt.show()

ArtistAnimation#

ArtistAnimation can be usedto generate animations if there is data stored on various different artists.This list of artists is then converted frame by frame into an animation. Forexample, when we useAxes.barh to plot a bar-chart, it creates a number ofartists for each of the bar and error bars. To update the plot, one wouldneed to update each of the bars from the container individually and redrawthem. Instead,animation.ArtistAnimation can be used to plot each frameindividually and then stitched together to form an animation. A barchart raceis a simple example for this.

fig,ax=plt.subplots()rng=np.random.default_rng(19680801)data=np.array([20,20,20,20])x=np.array([1,2,3,4])artists=[]colors=['tab:blue','tab:red','tab:green','tab:purple']foriinrange(20):data+=rng.integers(low=0,high=10,size=data.shape)container=ax.barh(x,data,color=colors)artists.append(container)ani=animation.ArtistAnimation(fig=fig,artists=artists,interval=400)plt.show()

Saving Animations#

To save animations using any of the writers, we can use theanimation.Animation.save method. It takes thefilename that we want tosave the animation as and thewriter, which is either a string or a writerobject. It also takes anfps argument. This argument is different than theinterval argument thatFuncAnimation orArtistAnimation uses.fps determines the frame rate that thesaved animation uses, whereasinterval determines the frame rate thatthedisplayed animation uses.

Below are a few examples that show how to save an animation with differentwriters.

Pillow writers:

ani.save(filename="/tmp/pillow_example.gif",writer="pillow")ani.save(filename="/tmp/pillow_example.apng",writer="pillow")

HTML writers:

ani.save(filename="/tmp/html_example.html",writer="html")ani.save(filename="/tmp/html_example.htm",writer="html")ani.save(filename="/tmp/html_example.png",writer="html")

FFMpegWriter:

ani.save(filename="/tmp/ffmpeg_example.mkv",writer="ffmpeg")ani.save(filename="/tmp/ffmpeg_example.mp4",writer="ffmpeg")ani.save(filename="/tmp/ffmpeg_example.mjpeg",writer="ffmpeg")

Imagemagick writers:

ani.save(filename="/tmp/imagemagick_example.gif",writer="imagemagick")ani.save(filename="/tmp/imagemagick_example.webp",writer="imagemagick")ani.save(filename="apng:/tmp/imagemagick_example.apng",writer="imagemagick",extra_args=["-quality","100"])

(theextra_args forapng are needed to reduce filesize by ~10x)

Note thatffmpeg andimagemagick need to be separately installed.A cross-platform way to obtainffmpeg is to install theimageio_ffmpegPyPI package, and then to setrcParams["animation.ffmpeg_path"]=imageio_ffmpeg.get_ffmpeg_exe().

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