#!/usr/bin/env python
# coding: utf-8

# # A Simple Animation: The Magic Triangle

# *This notebook originally appeared as a post on*
# [*Pythonic Perambulations*](http://jakevdp.github.io/blog/2013/05/28/a-simple-animation-the-magic-triangle/)

# <!-- PELICAN_BEGIN_SUMMARY -->
# I've been spending a lot of time lately playing with animations in
# IPython notebook.  Here's my latest one - a slightly puzzling
# rearrangement of shapes into two different triangles:

# <img src="http://jakevdp.github.io/images/MagicTriangle.gif">

# Where does the extra block go?  Look close and you might be able to figure it out.
# <!-- PELICAN_END_SUMMARY -->

# I created the animation using just a few lines of matplotlib.  Here we'll display it using the
# [Javascript Animation widget](http://jakevdp.github.io/blog/2013/05/19/a-javascript-viewer-for-matplotlib-animations/)
# that I wrote:

# In[1]:


get_ipython().run_line_magic('pylab', 'inline')


# In[2]:


# JS Animation import is available at http://github.com/jakevdp/JSAnimation
from JSAnimation.IPython_display import display_animation
from matplotlib import animation

# Set up the axes, making sure the axis ratio is equal
fig = plt.figure(figsize=(6.5, 2.5))
ax = fig.add_axes([0, 0, 1, 1], xlim=(-0.02, 13.02), ylim=(-0.02, 5.02),
                  xticks=range(14), yticks=range(6), aspect='equal', frameon=False)
ax.grid(True)

# Define the shapes of the polygons
P1 = np.array([[0, 0], [5, 0], [5, 2], [0, 0]])
P2 = np.array([[0, 0], [8, 0], [8, 3], [0, 0]])
P3 = np.array([[0, 0], [5, 0], [5, 1], [3, 1], [3, 2], [0, 2], [0, 0]])
P4 = np.array([[0, 1], [3, 1], [3, 0], [5, 0], [5, 2], [0, 2], [0, 1]])

# Draw the empty polygons for the animation
kwds = dict(ec='k', alpha=0.5)
patches = [ax.add_patch(plt.Polygon(0 * P1, fc='g', **kwds)),
           ax.add_patch(plt.Polygon(0 * P2, fc='b', **kwds)),
           ax.add_patch(plt.Polygon(0 * P3, fc='y', **kwds)),
           ax.add_patch(plt.Polygon(0 * P4, fc='r', **kwds))]

# This function moves the polygons as a function of the frame i
Nframes = 30
def animate(nframe):
    f = nframe / (Nframes - 1.0)
    patches[0].set_xy(P1 + (8 - 8 * f, 3 - 3 * f + 0.5 * np.sin(f * np.pi)))
    patches[1].set_xy(P2 + (5 * f, 2 * f - 0.5 * np.sin(f * np.pi)))
    patches[2].set_xy(P3 + (8 - 3 * f, 0))
    patches[3].set_xy(P4 + (8, 1 - f))
    return patches
    
anim = animation.FuncAnimation(fig, animate, frames=Nframes, interval=50)
display_animation(anim, default_mode='once')


# For a brief tutorial on creating matplotlib animations, see my
# [previous post](http://jakevdp.github.io/blog/2012/08/18/matplotlib-animation-tutorial/)
# on the subject.

# By the way, the animated gif at the head of this post was created using the following script.
# It's similar to above, except we add some extra frames to create the patrol-loop
# and the pause at each end.
# 
# Note that saving the animation as an animated gif requires both matplotlib
# version 1.3+ and the [imagemagick](http://www.imagemagick.org/) command.

# In[3]:


def animate_as_gif(nframe):
    if nframe >= Nframes and nframe < Nframes + 15:
        nframe = Nframes - 1
    elif nframe >= Nframes + 15 and nframe < 2 * Nframes + 15:
        nframe = 2 * Nframes + 14 - nframe
    elif nframe >= 2 * Nframes + 15:
        nframe = 0
    return animate(nframe)
    
anim = animation.FuncAnimation(fig, animate_as_gif,
                               frames=2 * Nframes + 30, interval=50)
anim.save('MagicTriangle.gif', writer='imagemagick')


# Enjoy!

# *This post was written in an IPython notebook, which can be downloaded*
# [*here*](http://jakevdp.github.io/downloads/notebooks/MagicTriangle.ipynb),
# *or viewed statically*
# [*here*](http://nbviewer.ipython.org/url/jakevdp.github.io/downloads/notebooks/MagicTriangle.ipynb).