pytutorial/matplotlib/animation_and_slider

Animation and Slider

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* TOC {:toc}

The goal

Questions to David Rotermund

Test data

import numpy as np
import matplotlib.pyplot as plt

axis = np.arange(-100, 101) / 100.0

x = axis[:, np.newaxis, np.newaxis].copy()
y = axis[np.newaxis, :, np.newaxis].copy()
z = axis[np.newaxis, np.newaxis, :].copy()

r = np.sqrt(x**2 + y**2 + z**2)

mask_0 = r > 0.75
r = 1.0 / (r + 1.0)
r[mask_0] = 0

plt.imshow(r[100, :, :], cmap="hot")
plt.colorbar()
plt.title("Cut through center of x-axis")
plt.show()

Animation

functools.partial

functools.partial(func, /, *args, **keywords)

Return a new partial object which when called will behave like func called with the positional arguments args and keyword arguments keywords. If more arguments are supplied to the call, they are appended to args. If additional keyword arguments are supplied, they extend and override keywords.

matplotlib.animation.FuncAnimation

class matplotlib.animation.FuncAnimation(fig, func, frames=None, init_func=None, fargs=None, save_count=None, *, cache_frame_data=True, **kwargs)

fig: Figure

The figure object used to get needed events, such as draw or resize.

func: callable

The function to call at each frame. The first argument will be the next value in frames. Any additional positional arguments can be supplied using functools.partial or via the fargs parameter.

It is often more convenient to provide the arguments using functools.partial. In this way it is also possible to pass keyword arguments. To pass a function with both positional and keyword arguments, set all arguments as keyword arguments, just leaving the frame argument unset:

def func(frame, art, *, y=None):
    ...

ani = FuncAnimation(fig, partial(func, art=ln, y='foo'))

frames : iterable, int, generator function, or None, optional

Source of data to pass func and each frame of the animation

If an iterable, then simply use the values provided. If the iterable has a length, it will override the save_count kwarg.

If an integer, then equivalent to passing range(frames)

If a generator function, then must have the signature:

def gen_function() -> obj

If None, then equivalent to passing itertools.count.

In all of these cases, the values in frames is simply passed through to the user-supplied func and thus can be of any type.

interval : int, default: 200 Delay between frames in milliseconds.

repeat_delay : int, default: 0 The delay in milliseconds between consecutive animation runs, if repeat is True.

repeat : bool, default: True Whether the animation repeats when the sequence of frames is completed.

Example

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation
from functools import partial


def next_frame(
    i: int, images: np.ndarray, image_handle: matplotlib.image.AxesImage
) -> None:
    image_handle.set_data(images[i, :, :])
    plt.title(f"Position: {i}")
    return


axis = np.arange(-100, 101) / 100.0

x = axis[:, np.newaxis, np.newaxis].copy()
y = axis[np.newaxis, :, np.newaxis].copy()
z = axis[np.newaxis, np.newaxis, :].copy()

r = np.sqrt(x**2 + y**2 + z**2)

mask_0 = r > 0.75
r = 1.0 / (r + 1.0)
r[mask_0] = 0

number_of_frames: int = r.shape[0]
repeat_movie: bool = False
interval_between_frames_in_ms: int = 100

fig: matplotlib.figure.Figure = plt.figure()
# Generate the initial image
# and set the value range for the whole images array
image_handle = plt.imshow(r[0, :, :], vmin=r.min(), vmax=r.max(), cmap="hot")
plt.colorbar()

animation = matplotlib.animation.FuncAnimation(
    fig,
    partial(next_frame, images=r, image_handle=image_handle),
    frames=number_of_frames,
    interval=interval_between_frames_in_ms,
    repeat=repeat_movie,
)

plt.show()

Interactive Python session

There are several options if you don't run it from VS Code interactively. One options is this:

# %%
%matplotlib widget