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"""
===============
Rain simulation
===============
Simulates rain drops on a surface by animating the scale and opacity
of 50 scatter points.
Author: Nicolas P. Rougier
Output generated via `matplotlib.animation.Animation.to_jshtml`.
"""
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.animation import FuncAnimation
# Fixing random state for reproducibility
np.random.seed(19680801)
# Create new Figure and an Axes which fills it.
fig = plt.figure(figsize=(7, 7))
ax = fig.add_axes([0, 0, 1, 1], frameon=False)
ax.set_xlim(0, 1), ax.set_xticks([])
ax.set_ylim(0, 1), ax.set_yticks([])
# Create rain data
n_drops = 50
rain_drops = np.zeros(n_drops, dtype=[('position', float, (2,)),
('size', float),
('growth', float),
('color', float, (4,))])
# Initialize the raindrops in random positions and with
# random growth rates.
rain_drops['position'] = np.random.uniform(0, 1, (n_drops, 2))
rain_drops['growth'] = np.random.uniform(50, 200, n_drops)
# Construct the scatter which we will update during animation
# as the raindrops develop.
scat = ax.scatter(rain_drops['position'][:, 0], rain_drops['position'][:, 1],
s=rain_drops['size'], lw=0.5, edgecolors=rain_drops['color'],
facecolors='none')
def update(frame_number):
# Get an index which we can use to re-spawn the oldest raindrop.
current_index = frame_number % n_drops
# Make all colors more transparent as time progresses.
rain_drops['color'][:, 3] -= 1.0/len(rain_drops)
rain_drops['color'][:, 3] = np.clip(rain_drops['color'][:, 3], 0, 1)
# Make all circles bigger.
rain_drops['size'] += rain_drops['growth']
# Pick a new position for oldest rain drop, resetting its size,
# color and growth factor.
rain_drops['position'][current_index] = np.random.uniform(0, 1, 2)
rain_drops['size'][current_index] = 5
rain_drops['color'][current_index] = (0, 0, 0, 1)
rain_drops['growth'][current_index] = np.random.uniform(50, 200)
# Update the scatter collection, with the new colors, sizes and positions.
scat.set_edgecolors(rain_drops['color'])
scat.set_sizes(rain_drops['size'])
scat.set_offsets(rain_drops['position'])
# Construct the animation, using the update function as the animation director.
animation = FuncAnimation(fig, update, interval=10, save_count=100)
plt.show()
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