matplotlib · pelson · May 14, 2014 · May 7, 2014 · May 7, 2014 · May 7, 2014
diff --git a/examples/animation/rain.py b/examples/animation/rain.py
@@ -0,0 +1,66 @@
+"""
+Rain simulation
+
+Simulates rain drops on a surface by animating the scale and opacity
+of 50 scatter points.
+
+Author: Nicolas P. Rougier
+"""
+import numpy as np
+import matplotlib.pyplot as plt
+from  matplotlib.animation import FuncAnimation
+
+
+# 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, 1),
+                                      ('growth',   float, 1),
+                                      ('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)
+plt.show()