Table of Contents
The easiest way to make a live animation in matplotlib is to use one of the
| ||Makes an animation by repeatedly calling a function |
| ||Animation using a fixed set of |
In both cases it is critical to keep a reference to the instance object. The animation is advanced by a timer (typically from the host GUI framework) which the
Animation object holds the only reference to. If you do not hold a reference to the
Animation object, it (and hence the timers), will be garbage collected which will stop the animation.
See Helper Classes below for details about what movie formats are supported.
The inner workings of
FuncAnimation is more-or-less:
for d in frames: artists = func(d, *fargs) fig.canvas.draw_idle() fig.canvas.start_event_loop(interval)
with details to handle ‘blitting’ (to dramatically improve the live performance), to be non-blocking, not repeatedly start/stop the GUI event loop, handle repeats, multiple animated axes, and easily save the animation to a movie file.
‘Blitting’ is a old technique in computer graphics. The general gist is to take an existing bit map (in our case a mostly rasterized figure) and then ‘blit’ one more artist on top. Thus, by managing a saved ‘clean’ bitmap, we can only re-draw the few artists that are changing at each frame and possibly save significant amounts of time. When using blitting (by passing
blit=True) the core loop of
FuncAnimation gets a bit more complicated
ax = fig.gca() def update_blit(artists): fig.canvas.restore_region(bg_cache) for a in artists: a.axes.draw_artist(a) ax.figure.canvas.blit(ax.bbox) artists = init_func() for a in artists: a.set_animated(True) fig.canvas.draw() bg_cache = fig.canvas.copy_from_bbox(ax.bbox) for f in frames: artists = func(f, *fargs) update_blit(artists) fig.canvas.start_event_loop(interval)
This is of course leaving out many details (such as updating the background when the figure is resized or fully re-drawn). However, this hopefully minimalist example gives a sense of how
func are used inside of
FuncAnimation and the theory of how ‘blitting’ works.
The expected signature on
init_func is very simple to keep
FuncAnimation out of your book keeping and plotting logic, but this means that the callable objects you pass in must know what artists they should be working on. There are several approaches to handling this, of varying complexity and encapsulation. The simplest approach, which works quite well in the case of a script, is to define the artist at a global scope and let Python sort things out. For example
import numpy as np import matplotlib.pyplot as plt from matplotlib.animation import FuncAnimation fig, ax = plt.subplots() xdata, ydata = ,  ln, = plt.plot(, , 'ro', animated=True) def init(): ax.set_xlim(0, 2*np.pi) ax.set_ylim(-1, 1) return ln, def update(frame): xdata.append(frame) ydata.append(np.sin(frame)) ln.set_data(xdata, ydata) return ln, ani = FuncAnimation(fig, update, frames=np.linspace(0, 2*np.pi, 128), init_func=init, blit=True) plt.show()
The second method is to us
functools.partial to ‘bind’ artists to function. A third method is to use closures to build up the required artists and functions. A fourth method is to create a class.
The provided writers fall into two broad categories: pipe-based and file-based. The pipe-based writers stream the captured frames over a pipe to an external process. The pipe-based variants tend to be more performant, but may not work on all systems.
| ||Pipe-based ffmpeg writer.|
| ||File-based animated gif writer.|
| ||Pipe-based avconv writer.|
Alternatively the file-based writers save temporary files for each frame which are stitched into a single file at the end. Although slower, these writers can be easier to debug.
| ||File-based ffmpeg writer.|
| ||Pipe-based animated gif.|
| ||File-based avconv writer.|
MovieWriter provides a way to grab sequential frames from the same underlying
Figure object. The base class
MovieWriter implements 3 methods and a context manager. The only difference between the pipe-based and file-based writers is in the arguments to their respective
setup() method is used to prepare the writer (possibly opening a pipe), successive calls to
grab_frame() capture a single frame at a time and
finish() finalizes the movie and writes the output file to disk. For example
moviewriter = MovieWriter(...) moviewriter.setup(fig=fig, 'my_movie.ext', dpi=100) for j in range(n): update_figure(n) moviewriter.grab_frame() moviewriter.finish()
If using the writer classes directly (not through
Animation.save), it is strongly encouraged to use the
saving context manager
with moviewriter.saving(fig, 'myfile.mp4', dpi=100): for j in range(n): update_figure(n) moviewriter.grab_frame()
to ensures that setup and cleanup are performed as necessary.
| ||This class wraps the creation of an animation using matplotlib.|
A module-level registry is provided to map between the name of the writer and the class to allow a string to be passed to
Animation.save instead of a writer instance.
| ||Registry of available writer classes by human readable name.|
To reduce code duplication base classes
| ||Abstract base class for writing movies.|
| ||Base class for writing movies.|
and mixins are provided
| ||Mixin class for avconv output.|
| ||Mixin class for FFMpeg output.|
| ||Mixin class for ImageMagick output.|
See the source code for how to easily implement new
Deprecated since version 2.0.
Deprecated since version 2.0.
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