FuncAnimation that adds lines on each frame. No removal.

additive_animation.py

import matplotlib.pyplot as plt
import numpy as np

from matplotlib.animation import FuncAnimation
from IPython.display import Video

# Make a spiral
step_count = 10000

random = np.random.RandomState(0)
k, phi = np.cumsum(random.uniform(0, 0.5, size=(step_count, 2)), axis=0).T
x = (k ** 0.7) * np.cos(phi)
y = (k ** 0.7) * np.sin(phi)
path = np.transpose([x, y])

# Render animation
frame_step = 10
frame_interval_milliseconds = 10
video_bitrate_kbps = 512
video_filename = "_a.mp4"

def plot_fragment(ax, fragment):
    ax.plot(fragment[:, 0], fragment[:, 1], lw=0.1, color="red")


fig, ax = plt.subplots(figsize=(2, 2), dpi=200)

ax.set_xlim(-250, 250)
ax.set_ylim(-250, 250)
ax.set_xticklabels([])
ax.set_yticklabels([])
ax.set_aspect("equal")

frame_count = step_count // frame_step

def draw_frame(frame):
    start = frame * frame_step
    end = (frame + 1) * frame_step + 1
    fragment = path[start:end]
    plot_fragment(ax, fragment)

anim = FuncAnimation(
    fig,
    draw_frame,
    frames=range(frame_count),
    interval=frame_interval_milliseconds,
)
anim.save(video_filename, bitrate=video_bitrate_kbps)

plt.close(fig)

Video(video_filename)