

.. _sphx_glr_gallery_animation_rain.py:


===============
Rain simulation
===============

Simulates rain drops on a surface by animating the scale and opacity
of 50 scatter points.

Author: Nicolas P. Rougier




.. image:: /gallery/animation/images/sphx_glr_rain_001.png
    :align: center





.. code-block:: python

    import numpy as np
    import matplotlib.pyplot as plt
    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, 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()

**Total running time of the script:** ( 0 minutes  0.104 seconds)



.. container:: sphx-glr-footer


  .. container:: sphx-glr-download

     :download:`Download Python source code: rain.py <rain.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: rain.ipynb <rain.ipynb>`

.. rst-class:: sphx-glr-signature

    `Generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_
